Salsolinol-a potential inhibitor of the gonadotropic axis in sheep during lactation.

This study tested the hypothesis that salsolinol, a derivative of dopamine, affects GnRH and LH secretion in lactating sheep. In the in vivo experiment, the structural analogue of salsolinol, 1-methyl-3,4-dihydroisoquinoline (1-MeDIQ), was infused into the infundibular nucleus-median eminence of sheep at the fifth wk of lactation to antagonize salsolinol's action. Simultaneously, cerebrospinal fluid from the third brain ventricle, to determine GnRH concentration, and plasma samples, to measure LH concentration, were collected. In the in vitro experiment, the anterior pituitary (AP) explants from weaned sheep were incubated in culture medium containing 2 doses of salsolinol, 20 and 100 µg/mL (S20 and S100, respectively). The concentration of LH in the collected media and relative expression of LHß subunit messenger RNA in the AP explants were determined. No significant difference was found in mean GnRH concentration in response to 1-MeDIQ infusion, but both mean plasma LH concentration and LH pulse frequency increased significantly (P < 0.001 and P < 0.05, respectively) compared with those in controls. Significantly higher LH concentrations occurred during the first (P < 0.001), second (P < 0.001), and fourth (P < 0.05) h of 1-MeDIQ infusion. In the in vitro study, both the S20 and S100 doses of salsolinol caused a significant decrease in the mean medium LH concentration compared with that in the control (P < 0.01 and P < 0.001, respectively). Salsolinol had no effect on the relative LHß subunit messenger RNA expression in the incubated tissue. In conclusion, salsolinol is a potential inhibitor of the secretory activity of the gonadotropic axis in lactating sheep, at least at the AP level. Although no significant changes in GnRH release were directly confirmed, an increase in the frequency of LH pulses does not allow to exclude the central action of salsolinol.

Reciprocal changes in leptin and NPY during nutritional acceleration of puberty in heifers.

Feeding a high-concentrate diet to heifers during the juvenile period, resulting in increased body weight (BW) gain and adiposity, leads to early-onset puberty. In this study, we tested the hypothesis that the increase in GnRH/LH release during nutritional acceleration of puberty is accompanied by reciprocal changes in circulating leptin and central release of neuropeptide Y (NPY). The heifers were weaned at 3.5 months of age and fed to gain either 0.5 (Low-gain; LG) or 1.0 kg/day (High-gain; HG) for 30 weeks. A subgroup of heifers was fitted surgically with third ventricle guide cannulas and was subjected to intensive cerebrospinal fluid (CSF) and blood sampling at 8 and 9 months of age. Mean BW was greater in HG than in LG heifers at week 6 of the experiment and remained greater thereafter. Starting at 9 months of age, the percentage of pubertal HG heifers was greater than that of LG heifers, although a replicate effect was observed. During the 6-h period in which CSF and blood were collected simultaneously, all LH pulses coincided with or shortly followed a GnRH pulse. At 8 months of age, the frequency of LH pulses was greater in the HG than in the LG group. Beginning at 6 months of age, concentrations of leptin were greater in HG than in LG heifers. At 9 months of age, concentrations of NPY in the CSF were lesser in HG heifers. These observations indicate that increased BW gain during juvenile development accelerates puberty in heifers, coincident with reciprocal changes in circulating concentrations of leptin and hypothalamic NPY release.

A novel animal model to study hot flashes: no effect of gonadotropin-releasing hormone.

OBJECTIVE: Menopausal hot flashes compromise the quality of life for most women. The physiological mechanisms underlying hot flashes remain poorly understood, and the absence of an animal model to investigate hot flashes hinders investigations in this field. METHODS: We first developed the sheep as a model to study peripheral skin temperature changes using fever-inducing lipopolysaccharide (LPS; 200 microg/kg) administered to ovary-intact ewes. Because a strong correlation between luteinizing hormone pulses and hot flashes has previously been reported, we then determined whether intravenous gonadotropin-releasing hormone (GnRH; 1 mg), a dose sufficient to elevate cerebrospinal fluid-GnRH concentrations, could modulate ear skin temperature in both ovariectomized and low-estrogen-replaced ovariectomized ewes. RESULTS: Some ewes responded to LPS in heart rate and abdominal temperature, but there was no significant effect on either parameter or cheek temperature for the group. In contrast, LPS injection caused a significant (P < 0.001) change in skin temperature at the ear. Ear temperature showed no significant change in response to GnRH relative to control injections in both ovariectomized and low estrogen ewes. CONCLUSIONS: We developed a model animal system in the ewe that can accurately detect small changes in peripheral skin temperature. This system has the potential to be extremely useful in future studies investigating the pathology of hot flashes and holds several advantages over previous model systems developed for this research. GnRH per se does not seem to be involved in thermoregulatory events.

Gonadotropin-releasing hormone in third ventricular cerebrospinal fluid: endogenous distribution and exogenous uptake.

GnRH is detectable in the cerebrospinal fluid (CSF), but its source remains unidentified. Previous studies have harvested CSF for GnRH analysis from the median eminence region, but it is unknown whether GnRH in CSF is restricted to this region. If CSF-GnRH plays a physiological role, through volume transmission, to communicate with brain regions that express GnRH receptors but are not evidently innervated by GnRH neurons, then it is essential to establish whether GnRH is more pervasive throughout the cerebroventricular system. Three cannulae were placed in the supraoptic, infundibular, and pineal recesses of the third ventricle. GnRH was undetectable in lateral ventricle CSF. GnRH pulses were detected in all ewes in infundibular recess CSF, but at sites more rostral (supraoptic) and caudal (pineal), GnRH pulse frequency and amplitude significantly (P<0.05) decreased. A GnRH surge was evident in CSF collected simultaneously from all cannulae, but the amplitude was greatest (P<0.05) at the infundibular recess. A final study established whether iv administered GnRH enters the CSF. A 250-ng GnRH dose did not affect CSF-GnRH concentrations (1.6+/-0.3 pg/ml), but 2.5 microg (2.7+/-0.2 pg/ml; P<0.001) and 1 mg (38.5+/-10.6 pg/ml; P<0.05) significantly increased CSF-GnRH concentrations. The present study shows: 1) the median eminence region is likely to be the major, if not only, source of GnRH entering the cerebroventricular system; and 2) exogenous GnRH crosses the blood-brain barrier, but extremely high doses are required to elevate CSF concentrations to physiological levels. Thus, CSF-GnRH may affect sites that are closer in proximity to the infundibular recess region than previously thought.

Kisspeptin synchronizes preovulatory surges in cyclical ewes and causes ovulation in seasonally acyclic ewes.

We determined whether kisspeptin could be used to manipulate the gonadotropin axis and ovulation in sheep. First, a series of experiments was performed to determine the gonadotropic responses to different modes and doses of kisspeptin administration during the anestrous season using estradiol-treated ovariectomized ewes. We found that: 1) injections (iv) of doses as low as 6 nmol human C-terminal Kiss1 decapeptide elevate plasma LH and FSH levels, 2) murine C-terminal Kiss1 decapeptide was equipotent to human C-terminal Kiss1 decapeptide in terms of the release of LH or FSH, and 3) constant iv infusion of kisspeptin induced a sustained release of LH and FSH over a number of hours. During the breeding season and in progesterone-synchronized cyclical ewes, constant iv infusion of murine C-terminal Kiss1 decapeptide-10 (0.48 mumol/h over 8 h) was administered 30 h after withdrawal of a progesterone priming period, and surge responses in LH occurred within 2 h. Thus, the treatment synchronized preovulatory LH surges, whereas the surges in vehicle-infused controls were later and more widely dispersed. During the anestrous season, we conducted experiments to determine whether kisspeptin treatment could cause ovulation. Infusion (iv) of 12.4 nmol/h kisspeptin for either 30 or 48 h caused ovulation in more than 80% of kisspeptin-treated animals, whereas less than 20% of control animals ovulated. Our results indicate that systemic delivery of kisspeptin provides new strategies for the manipulation of the gonadotropin secretion and can cause ovulation in noncyclical females.

Hypothalamic tanycytes: a key component of brain-endocrine interaction.

Tanycytes are bipolar cells bridging the cerebrospinal fluid (CSF) to the portal capillaries and may link the CSF to neuroendocrine events. During the perinatal period a subpopulation of radial glial cells differentiates into tanycytes, a cell lineage sharing some properties with astrocytes and the radial glia, but displaying unique and distinct morphological, molecular, and functional characteristics. Four populations of tanycytes, alpha(1,2) and beta(1,2), can be distinguished. These subtypes express differentially important functional molecules, such as glucose and glutamate transporters; a series of receptors for neuropeptide and peripheral hormones; secretory molecules such as transforming growth factors, prostaglandin E(2), and the specific protein P85; and proteins of the endocytic pathways. This results in functional differences between the four subtypes of tanycytes. Thus, alpha(1,2) tanycytes do not have barrier properties, whereas beta(1,2) tanycytes do. Different types of tanycytes use different mechanisms to internalize and transport cargo molecules; compounds internalized via a clathrin-dependent endocytosis would only enter tanycytes from the CSF. There are also differences in the neuron-tanycyte relationships; beta(1,2) tanycytes are innervated by peptidergic and aminergic neurons, but alpha(1,2) tanycytes are not. Important aspects of the neuron-beta(1) tanycyte relationships have been elucidated. Tanycytes can participate in the release of gonadotropin-releasing hormone (GnRH) to the portal blood by expressing estrogen receptors, absorbing molecules from the CSF, and providing signal(s) to the GnRH neurons. Removal of tanycytes prevents the pulse of GnRH release into the portal blood, the peak of luteinizing hormone, and ovulation. The discovery in tanycytes of new functional molecules is opening a new field of research. Thus, thyroxine deiodinase type II, an enzyme generating triiodothyronine (T(3)) from thyroxine, appears to be exclusively expressed by tanycytes, suggesting that these cells are the main source of brain T(3). Glucose transporter-2 (GLUT-2), a low-affinity transporter of glucose and fructose, and ATP-sensitive K(+) channels are expressed by tanycytes, suggesting that they may sense CSF glucose concentrations.

Measurement and possible function of GnRH in cerebrospinal fluid in ewes.

Large mammal models are unique in that it is possible to analyse the real-time release of neural factors over several hours or even days in a conscious unstressed state. Until recently, hypophyseal portal blood sampling was the only reliable method available for this purpose. However, development of an alternative approach, in which cerebrospinal fluid (CSF) is collected from specific sites within the cerebroventricular system, has provided another route by which hypothalamic activity can be investigated. Use of this approach, in combination with other methods, such as intracerebroventricular infusion or simultaneous hypophyseal portal blood collection, has yielded exciting novel data that challenge long-held dogma on the pathways of communication in the brain. It is clear that factors in the CSF are released site-specifically and, thus, this fluid is not homogeneous; the concentration of a factor in lumbar CSF may bear no relation to its ventricular concentration. Data also indicate that there is little, if any, transfer of factors between the CSF and the hypophyseal portal system. In addition, there is mounting evidence indicating that factors in CSF may serve as part of a non-synaptic communication system in the brain. Establishing an unequivocal function for CSF-borne factors may prove technically difficult, if not impossible. However, we believe that there is strong evidence supporting a role for one such factor, GnRH in CSF, in sexual behaviour.

Neuroendocrine mechanisms underlying the effects of progesterone on the oestradiol-induced GnRH/LH surge.

Oestradiol provides the drive to reproductive cyclicity in female mammals through its ability to stimulate the GnRH surge. In contrast, progesterone can be seen as the 'clutch and brakes' within reproductive cycles, as it can modify the response of the GnRH neurosecretory system to oestradiol. In this regard, progesterone has multiple and sometimes opposing effects on the GnRH neurosecretory system. For example, dependent upon the timing of exposure, progesterone enhances the amplitude of the oestradiol-induced LH (rats) and GnRH surge (within cerebrospinal fluid in sheep, mRNA concentrations in rats), but can also inhibit pulsatile GnRH secretion, and delay or even block expression of the surge (monkeys, rats and sheep). Investigations of the mechanisms of action of progesterone are complicated further by the fact that some of the observed effects of progesterone, such as the ability to block the oestradiol-induced surge, appear to be mediated via several different routes. Consequently, a variety of approaches are needed to advance our understanding of this fundamental reproductive neuroendocrine system. In this context, large animal neuroendocrine models have provided important information about the mechanisms of progesterone action and provide many exciting opportunities for future research.

Gonadotropin-releasing hormone in third ventricular cerebrospinal fluid of the heifer during the estrous cycle.

The release profile of GnRH in cerebrospinal fluid (CSF) and its correlation with LH in peripheral blood of ovary-intact heifers during the estrous cycle were investigated. A silicon catheter was placed into the third ventricle of six heifers using ultrasonography. During the mid-luteal phase, the heifers were injected with prostaglandin F(2alpha) to induce luteolysis. Surges of CSF GnRH (66.7 h after prostaglandin F(2alpha) administration) and peripheral LH (66.3 h) occurred simultaneously and were coincident with the onset of estrus (67.0 h). Duration of elevated GnRH concentration considerably overlapped with the estrous phase in each of the heifers. Mean pulse frequencies of both GnRH and LH were significantly higher during the proestrous and early luteal phases than during the mid-luteal phase, while mean concentration and pulse amplitude of both GnRH and LH were not different between these three phases. Of all the GnRH pulses identified, more than 80% were accompanied by an LH pulse during the proestrous and early luteal phases. However, the proportion of GnRH pulses that were coincident with an LH pulse during the mid-luteal phase decreased to 60%. The results clearly demonstrate that a dynamic (pulse) and longer-term (surge) changes of GnRH release into CSF are physiologically expressed during the estrous cycle in heifers, and the pattern of pulsatile GnRH secretion in heifers depends upon their estrous cycle.

Progesterone priming is essential for the full expression of the positive feedback effect of estradiol in inducing the preovulatory gonadotropin-releasing hormone surge in the ewe.

The luteal phase elevation in circulating progesterone (P) powerfully inhibits GnRH and, consequently, LH release, thereby preventing premature preovulatory LH surges in the ewe. Whether luteal phase P modulates the response of the GnRH system to the positive feedback effect of estradiol is unknown. To investigate this possibility, two experiments were conducted during the anestrous season using an artificial model of the follicular phase in ovariectomized ewes bearing 10-mm s.c. 17beta-estradiol SILASTIC brand implants (Dow Coming Corp.). In Exp 1, ewes (n = 10) were run through four successive artificial cycles during which a luteal phase level of P was either replaced (cycles 1 and 3) or not replaced (cycles 2 and 4). GnRH and LH secretions were monitored by sampling cerebrospinal fluid (CSF) and jugular blood from 10-35 h after four 30-mm 17beta-estradiol SILASTIC implants were inserted sc. CSF could be collected from only four ewes over the four cycles. There was no P-dependent difference in the onset of the GnRH and LH surges, which may have been due to a progressive delay in the surge onsets over the four cycles (by ANOVA, P < 0.05). Due to this delay, it was not possible to obtain an accurate estimate of the duration of the GnRH and LH surges in all ewes, but the size of the GnRH surge was always greater when animals had been treated with P, resulting in a significant increase in the maximum (P < 0.01) and mean (P < 0.05) levels during the surge. In contrast, there was no effect on any parameter of LH secretion. In Exp 2, ewes (n = 10) were run through two artificial estrous cycles during which luteal phase P was either replaced or not replaced, using a cross-over experimental design. CSF was collected from seven ewes over the two cycles. GnRH and LH secretions were monitored from 10-53 h after estradiol administration. As in Exp 1, a clear significant increase in the maximal and mean GnRH levels (P < 0.05 for both) was observed during the surge when ewes had been pretreated with P. Again, no changes were observed in LH release during the surge. P priming did, however, delay the onsets of the GnRH (P < 0.01) and LH surges (P < 0.01). Our data show that the increase in P during the luteal phase of the estrous cycle is essential for the full expression of the positive feedback effect of estradiol in inducing the preovulatory GnRH surge in the ewe.

Increase in gonadotropin-releasing hormone (GnRH) levels in CSF after stimulation of the nervus terminalis in Atlantic stingray, Dasyatis sabina.

The nervus terminalis (NT) contains many cells immunoreactive to gonadotropin-releasing hormone (GnRH). The potential of the NT to release GnRH in vivo was investigated by stimulating the peripheral nerve trunk of Atlantic stingrays and collecting cerebrospinal fluid (CSF). The CSF samples from stimulated animals averaged about twice the levels of mGnRH-like peptide as those of unstimulated animals. These results demonstrate that nervus terminalis activity can effect in vivo GnRH levels in the brain.

Gonadotropin-releasing hormone secretion into third-ventricle cerebrospinal fluid of cattle: correspondence with the tonic and surge release of luteinizing hormone and its tonic inhibition by suckling and neuropeptide Y.

Objectives of the current studies were to characterize the pattern of GnRH secretion in the cerebrospinal fluid of the bovine third ventricle, determine its correspondence with the tonic and surge release of LH in ovariectomized cows, and examine the dynamics of GnRH pulse generator activity in response to known modulators of LH release (suckling; neuropeptide Y [NPY]). In ovariectomized cows, both tonic release patterns and estradiol-induced surges of GnRH and LH were highly correlated (0.95; p < 0.01). Collectively, LH pulses at the baseline began coincident with (84%) or within one sampling point after (100%) the onset of a GnRH pulse, and all estradiol-induced LH surges were accompanied by corresponding surges of GnRH. A 500- microg dose of NPY caused immediate cessation of LH pulses and lowered (p < 0.001) plasma concentrations of LH for at least 4 h. This corresponded with declines (p < 0.05) in both GnRH pulse amplitude and frequency, but GnRH pulses were completely inhibited for only 1.5-3 h. In intact, anestrous cows, GnRH pulse frequency did not differ before and 48-54 h after weaning on Day 18 postpartum, but concentrations of GnRH (p < 0.05) and amplitudes of GnRH pulses (4 of 7 cows) increased in association with weaning and heightened secretion of LH. We conclude that the study of GnRH secretory dynamics in third-ventricle CSF provides a reasonable approach for examining the activity and regulation of the hypothalamic pulse generator in adult cattle. However, data generated using this approach must be interpreted in their broadest context. Although strong neurally mediated inhibitors of LH pulsatility (suckling; NPY) had robust effects on one or more GnRH secretory characteristics in CSF, only high doses of NPY briefly abolished GnRH pulses. This implies that the GnRH signal received at the hypophyseal portal vessels under these conditions may differ quantitatively or qualitatively from those in CSF, and theoretically would be undetectable or below a biologically effective threshold when LH pulses are absent.

Does gonadotropin-releasing hormone in the cerebrospinal fluid modulate luteinizing hormone release?

The function of gonadotropin-releasing hormone (GnRH) in the cerebrospinal fluid (CSF) is unknown. This study on ovariectomized ewes investigated whether CSF-GnRH has a role in modulating luteinizing hormone (LH) secretion either through an ultrashort-loop feedback system to affect GnRH secretion or to directly act on the pituitary gland after entering the hypothalamo-hypophysial portal system. In the first experiment, a 3-hour continuous infusion of exogenous GnRH (700 or 7 pg/min; n = 8) was administered into the third ventricle through a permanent indwelling cannula. Jugular LH concentrations were measured as an estimate of the activity of the GnRH 'pulse generator'. To assess the potential for a direct involvement of CSF-GnRH in pituitary stimulation of LH secretion, ewes were also implanted with a cannula to collect hypophysial portal blood. In a first investigation, radioactive (2 x 10(6) cpm 125I-GnRH; n = 3) GnRH was injected into the third ventricle, and the amount of radioactivity present in the portal and jugular blood after the injection measured. In a second investigation, cold GnRH was infused (400 pg/min; n = 3) into the third ventricle for 2 h, and portal and jugular blood collected for the determination of GnRH and LH concentrations, respectively. In the first experiment, neither rate of infusion of GnRH into the third ventricle had any effect on the mean interpulse interval, nadir, pulse amplitude or circulating level of systemic LH, suggesting that CSF-GnRH is not a component of an ultrashort-loop feedback system for GnRH. Furthermore, in the second experiment, despite extremely low levels of radioactivity (maximum: 120 cpm/ml) being detected in hypophysial portal blood (which may not have been intact decapeptide), in the second part of this experiment, no radioimmunoassayable GnRH associated with the period of infusion could be measured. These data demonstrate in ewes that little, if any, CSF-GnRH reaches the hypophysial portal blood, and this compartment of GnRH does not, thus, directly affect the pituitary gland. The present study strongly suggests, therefore, that CSF-GnRH does not modulate LH secretion. Whether this compartment of GnRH is involved in sexual behavior remains to be established.

Simultaneous measurement of gonadotropin-releasing hormone in the third ventricular cerebrospinal fluid and hypophyseal portal blood of the ewe.

GnRH is present in the hypophyseal portal blood and cerebrospinal fluid (CSF) of several species investigated, including sheep, but the precise relationship between these two compartments of GnRH is unknown. In the present study, ovariectomized steroid-treated ewes were surgically prepared for the simultaneous collection of portal blood and third ventricular CSF. Ten-minute samples were collected for pulse analysis after progesterone removal and hourly for comparisons during the estradiol-induced LH surge. The time of onset of the portal (15.3 +/- 0.5 h after estradiol) and CSF (15.9 +/- 0.2 h) GnRH surges was similar and occurred coincidentally with the LH surge (15.6 +/- 0.4 h). The period of the surge during which GnRH concentrations exceeded half-maximal levels (portal, 7.3 +/- 1.5 h; CSF, 7.3 +/- 0.3 h) was the same and outlasted the corresponding LH surge period (3.3 +/- 0.3 h). LH pulses started and peaked later than the corresponding portal GnRH pulses (onset difference, 10 +/- 1 min; peak difference, 16 +/- 1 min; P < 0.01 for both), but the times of pulse onset and peak were not significantly different from those of concomitant CSF GnRH pulses (onset difference, 8 +/- 6 min; peak difference, 8 +/- 4 min). Although the times of pulse onset and peak did not differ between the portal and CSF GnRH compartments (onset difference, 4 +/- 6 min; peak difference, 6 +/- 2 min), CSF GnRH pulses were longer than their portal counterparts (CSF, 38 +/- 3 min; portal, 15 +/- 1 min; P < 0.01). The amplitude of jugular LH pulses was strongly correlated (r2 = 0.85) with portal GnRH pulse amplitude, but not with that of CSF GnRH pulses (r2 = 0.45); there was no correlation between portal and CSF GnRH pulse amplitudes (r2 = 0.25). These data show that third ventricular CSF GnRH reliably relates neurosecretory events occurring within the hypophyseal portal system at the time of the preovulatory LH surge, but is not as precise as portal GnRH in marking a LH pulse.

GnRH secretion into CSF in rams treated with a GnRH antagonist.

The equilibrium of the brain-pituitary-testicular axis is controlled by negative feedback exerted primarily through changes in the circulating concentrations of gonadal steroids. This is usually studied in gonadectomised animals treated with single large doses or constant low levels of exogenous steroid. However, the feedback system probably also contains dynamic components, perhaps expressed as delays to changes in GnRH secretion following a change in steroid concentration. These delays must be measured without interference from surgical procedures, including anaesthesia, bias associated with changes in pituitary responsiveness (which affect the efficiency of pulse detection), and chronic side-effects of gonadectomy. We used a GnRH antagonist ['Antarelix': Ac-D-Nal, D-Cpa, D-Pal, Ser, Tyr, D-Hci, Leu, Lys-(iPr), Pro, D-Ala-NH2] to transiently block LH and steroid secretion (in effect, inducing and reversing castration) in mature male sheep, and measured GnRH secretion into cerebrospinal fluid (CSF) in the third cerebral ventricle. The CSF was withdrawn with a peristaltic pump at a rate of 2 ml/h and pooled every 20 min. Jugular plasma was sampled every 20 min and analysed for testosterone and LH pulses. The antagonist (500 microg i.v.) was injected after 6 h of baseline sampling and the study continued for a further 24 h. The pulses of LH and testosterone disappeared shortly after antagonist injection, with delays of 20 +/- 12 min for LH and 80 +/- 29 min for testosterone. This led to an increase in GnRH pulse frequency, starting 300 +/- 54 min after antagonist injection. Secretion of LH and testosterone pulses resumed at 553 +/- 38 and 530 +/- 30 min (after antagonist injection), and GnRH pulse frequency returned to baseline values after 170 +/- 42 min (relative to LH) and 117 +/- 35 min (relative to testosterone). The consistent nature of these responses across the group of animals suggests that this can be used to test the effects of exteroceptive factors on the dynamics of negative feedback.

Luteinizing hormone (LH)-releasing hormone in third ventricular cerebrospinal fluid of the ewe: correlation with LH pulses and the LH surge.

Morphological evidence suggests that LHRH may be secreted into cerebrospinal fluid (CSF), but only in the rhesus monkey has CSF LHRH been found to reflect changes occurring in the LHRH neuroendocrine system. This study investigated whether LHRH is detectable in ovine CSF and, if so, whether its release profile correlates with peripheral LH profiles during pulse and surge conditions. A polyethylene catheter was threaded through a stainless steel guide cannula previously implanted into the third ventricle of an ovariectomized ewe, which enabled continuous CSF withdrawal on repeated occasions. The first experiment (n = 3) showed that peripheral LH concentrations were unaffected by CSF removal at rates of 12, 30, 50, and 100 microliters/min, and the second (n = 4) established that CSF LHRH secretion was pulsatile, with considerable variation in pulse amplitude (6.3 +/- 1.8 pg/ml; range, 1.3-18.7 pg/ml). In the third experiment (n = 6), an endogenous LH surge was induced after progesterone withdrawal and 17 beta-estradiol administration. Although CSF LHRH (15.3 +/- 1.3 h) and peripheral LH (14.8 +/- 1.0 h) surges occurred simultaneously, CSF LHRH concentrations were greater than half-maximal levels for longer (11.0 +/- 0.6 h; P < 0.005) than LH concentrations (6.0 +/- 0.4 h). This is the first study in sheep to reveal the presence of LHRH in CSF and show that it expresses dynamic and longer term changes coincident with peripheral LH fluctuations. CSF LHRH analysis also permits repeated sampling from individuals and, therefore, long term within-individual comparisons.

Cerebrospinal fluid and plasma concentrations of SRIH, beta-endorphin, CRH, NPY and GHRH in obese and normal weight subjects.

Numerous hypothalamic peptides are involved in the control of eating behaviour. We assessed plasma and cerebrospinal fluid (CSF) levels of SRIH, beta-endorphin (beta-EP), CRH, NPY and GHRH in a group of massively obese patients and in normal weight subjects. In the obese patients, CSF SRIH and beta-EP levels were significantly reduced and increased, respectively, compared with controls (20.6 +/- 2.62, mean +/- s.e.m., vs 34.5 +/- 2.14 pg/ml, P < 0.05, for SRIH and 111.2 +/- 5.00 vs 80.4 +/- 5.32 pg/ml, P < 0.001, for beta-EP). Considering the data of obese and control subjects altogether, SRIH and beta-EP concentrations correlated negatively and positively, respectively, with BMI values (r = -0.641, P < 0.005 and r = 0.518, P < 0.05). No significant differences were observed in CSF levels of CRH, NPY and GHRH between obese and normal weight subjects, though GHRH levels were close to the assay sensitivity. CSF concentrations of CRH were positively correlated with those of SRIH in obese patients (r = 0.60, P < 0.05) and with those of NPY both in obese (r = 0.69, P < 0.02) and in control subjects (r = 0.83, P < 0.005). Plasma levels of SRIH, beta-EP, NPY and GHRH did not differ significantly in the two groups of subjects; plasma CRH was undetectable. Our results argue against the hypothesis of an enhanced SRIH tone as the cause of impaired GH secretion in obese patients, a primary defect in GHRH or GH release seems more likely. Moreover, they emphasise the importance of an increased tone of endogenous opioids in the pathophysiology of human obesity.

Immunocytochemical demonstration of neuropeptide Y and luteinizing hormone-releasing hormone-immunoreactive structures in the organum vasculosum laminae terminalis of juvenile gilts.

Immunocytochemical investigations on the immature gilt organum vasculosum laminae terminalis showed extensive neuropeptide Y- and luteinizing hormone-releasing hormone-immunoreactive innervation of the organ. The luteinizing hormone-releasing hormone-containing varicose fibers ran along the organum vasculosum laminae terminalis in close association with blood vessels. The nerve processes originating from well-stained luteinizing hormone-releasing hormone-immunoreactive perikarya were distributed around the organum vasculosum laminae terminalis. The matrix of the organum vasculosum laminae terminalis was abundantly supplied by neuropeptide Y-immunoreactive varicose fibers. Numerous neuropeptide Y-immunoreactive terminals seemed to penetrate the ependymal lining of the organ. From these observations, it is concluded that there are favorable morphological conditions for secretion of neuropeptide Y into the cerebrospinal fluid of the third ventricle and release of luteinizing hormone-releasing hormone into fenestrated capillaries of the organ.

A surge of gonadotropin-releasing hormone accompanies the estradiol-induced gonadotropin surge in the rhesus monkey.

In several species, the ovulatory LH surge is preceded by a surge of GnRH. Although a role for estradiol in the initiation of the LH surge is well established in the primate, several observations in the rhesus monkey have questioned whether such an estradiol-induced neurosecretory event takes place. We report on GnRH measurements in cerebrospinal fluid (CSF) samples obtained from the third ventricle of intact and ovariectomized (OVX) conscious rhesus monkeys during control periods and throughout the estradiol-induced positive feedback phase. In the first experiment, we measured control GnRH concentrations in CSF collected at 15-min intervals uninterruptedly for a period of 1-5 days in tethered OVX monkeys (n = 4) in their cages without steroid priming. As had been demonstrated previously with the same method in restrained animals, CSF from the third ventricle contained detectable amounts of GnRH. Spontaneous GnRH secretion was pulsatile; overall mean pulse interval was 67.4 (+/- 2.2 SE) min for a total of 177 GnRH pulses. During 2 periods (8 and 6 h) when simultaneous blood and CSF samples were obtained, 14 out of 15 GnRH pulses were accompanied by an LH pulse. To evaluate the effects of an estrogen challenge on GnRH secretion, estradiol benzoate (E2B; 330 micrograms) was given to 4 intact (5 experiments) and to 2 OVX monkeys. CSF collection was initiated 8-24 h before E2B injection and continued for 72-84 h thereafter. E2B administration resulted in a surge of LH and of GnRH in all but one experiment. The mean time of onset of the GnRH surge was 22.0 (+/- 4.0) h after E2B, whereas that of the LH surge was 24.7 (+/- 3.4) h. In contrast to LH, which declined after a peak at 35.2 +/- 3.9 h, the increase in GnRH secretion persisted throughout most of the observation period. The magnitude of the GnRH response differed in the 2 groups; in the intact animals, mean peak GnRH concentration increased 8.9-fold but only 3.8-fold in the OVX monkeys. A similar GnRH surge was observed in 1 OVX monkey, receiving an iv infusion of E2, which produced more physiological concentrations of E2. In this animal, an initial suppression of GnRH concentration in the 24-48 h period after E2 (GnRH control, 14.6 +/- 1.9; post-E2, 4.0 +/- 0.5 pg/ml) preceded the initiation of the GnRH surge which occurred at 54 h after E2.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunoreactive LHRH in cerebrospinal fluid: the clinical significance in intracranial diseases.

Cerebrospinal fluid (CSF) and plasma levels of luteinizing hormone-releasing hormone (LHRH) were measured by RIA in 46 patients with acute intracranial diseases, ie, cerebral bleeding (group A), cerebral thrombosis (B), head injury (C) and meningitis (D), and the results were compared to those obtained in 21 patients with non-intracranial diseases (group E; control). Immunoreactive LHRH concentrations in CSF (CSF IR-LHRH) of 8 postmenopausal women in group E ranged 1.3 to 6.1 (mean +/- SE: 3.1 +/- 0.6) pg/ml, and those of 5 other women and 8 men with group E ranged 1.0 to 5.6 (3.6 +/- 0.4)pg/ml. In 7 out of 15 patients in group A(7/15), CSF IR-LHRH were above the levels seen in group E. In group B, C and D, CSF IR-LHRH were above the control levels in 9/15, 1/9, 3/7, respectively. The changes in plasma LHRH were not clear in postmenopausal patients in groups A and B. Plasma IR-LHRH in other women and men in group A were above the control levels in 2 out of 9 patients (2/9). Those in groups B, C and D were above the control levels in 3/8, 1/9, 2/7, respectively. Moreover, both plasma and CSF IR-LHRH of 13 patients in group A or B in chronic stage were within the control ranges. In cases observed following the time course, the occasionally increased IR-LHRH in plasma and CSF tended to decrease following the abatement of the diseases.(ABSTRACT TRUNCATED AT 250 WORDS)