Administration of ACTH to restrained, pregnant sows alters their pigs' hypothalamic-pituitary-adrenal (HPA) axis.

This study was designed to examine the physiology and behavior of pigs whose dams were snared and then injected with ACTH during gestation. Administration of ACTH to dams during pregnancy has been shown to replicate the effects of prenatal stress in other species. Control sows (n = 8) were given no treatment, whereas the treatment sows (ACTH, n = 8) were immobilized by snaring the snout and then administered an i.v. injection of ACTH (1 IU/kg BW) weekly from 6 to 12 wk of gestation. A pig was killed from each sow at 1, 30, and 60 d of age. The hypothalamus, pituitary gland, adrenal glands, and liver were immediately obtained to determine the amounts of corticotropin-releasing hormone (CRH), beta-endorphin, and mRNA for pro-opiomelanocorticotropin (POMC), the ACTH receptor (ACTH-R), and insulin-like growth factor I (IGF-I). Pituitary corticotrope and somatotrope cell numbers and adrenal cortex-to-medulla area ratios (CORT:MED) were also determined. Pigs' behaviors were recorded at 6 and 8 wk of age. At 75 d of age, a blood sample was taken and a biopsy puncture was created on one pig from each litter, then pigs were stressed by mixing. Blood was sampled every other day for 10 d to determine plasma cortisol concentrations and differential leukocyte counts. Biopsy damage was evaluated for healing. At 1 d of age, control pigs tended to weigh more (P = .09), have a lower expression of ACTH-R mRNA (P = .01) and IGF-I mRNA (P = .01), and a lower CORT:MED (P = .04) than ACTH pigs. At 30 d of age, control pigs had a greater concentration of beta-endorphin (P = .01) and tended to have a lower concentration of CRH (P = .09) and IGF-I mRNA (P = .10) than ACTH pigs. At 60 d of age, control pigs tended to have lighter pituitary glands (P = .08), a lower expression of POMC mRNA (P = .02), and a CORT:MED (P = .003) than ACTH pigs. At 8 wk of age, control pigs performed a higher frequency of belly nosing (P = .07) and oral vice behaviors (P = .01) than ACTH pigs. In response to mixing stress, control pigs had lesser concentrations of plasma cortisol (P = .03) and healed faster (P = .006) than ACTH pigs. Thus, exogenous ACTH and restraint during gestation alters the HPA axis of the sow's offspring, and during stressful situations later in life health, and therefore welfare, may be compromised.

Endocrine and other responses to acute administration of cannabinoid compounds to non-stressed male calves.

There is an abundance of cannabinoid (CB) receptors for derivatives of cannabis plants in the brain and throughout the body, and several naturally occurring arachidonic acid derivatives can activate these receptors. The specific objective of this study was to activate these CB receptors in castrated male calves through administration of several CB agonists and to measure immediate changes in concentrations of several serum hormones, respiration rate, and sensitivity to pain. The rationale for the study was that exogenous activation of CB receptors might reveal whether the endogenous CB system (consisting of receptors and endogenous ligands) plays a role in the stress response of animals and specifically whether the activated CB system might be part of a coping mechanism to combat stress. Intravenous administration of three CB agonists (anandamide, methanandamide and WIN 55212-2) to nine castrated male calves under non-stress conditions provoked immediate increases of serum cortisol and respiration rate as well as rapidly caused hypoalgesia to cutaneous pain and thermal stimuli. Although anandamide and methanandamide did not affect serum prolactin, administration of another CB agonist (WIN 55212-2) did increase serum prolactin abruptly. None of the CB agonists affected serum growth hormone. In summary, many of the changes following administration of CB agonists were similar to a stress response in this species, but there were some agonist-specific differences, notably regarding prolactin secretion, as well as differences between calves and observations made in other species. Although CB receptors in calves may be activated by endogenous ligands during exposure to some stressors, the present results are also consistent with this CB system being part of a coping mechanism that helps animals deal with imposed stressors.

Hormonal and behavioral correlates of emotional states in sexually trained boars.

Physiological and behavioral traits of sexually mature boars were compared between episodes of copulation and sexual frustration in order to determine reliable indicators of the differences in emotional states. Ten boars, approximately 6 mo of age, were trained to mount a stationary artificial sow (ArtSow) and to ejaculate when digital pressure was applied to the extended penis. This method of semen collection is the typical procedure of the industry. All 10 boars used in this study were fully trained to this procedure before the onset of the study. Each boar was subjected to trials in which one of the following two treatments was applied. In the control (CTRL) treatment, boars were treated the same as during their training (i.e., allowed to complete ejaculation). In the frustration (FRUS) treatment, boars were allowed to mount the ArtSow, but because no manual pressure was applied to the extended penis, ejaculation never occurred. Blood was collected via indwelling catheters before onset of the trial, during exposure to the ArtSow, and after returning to their home pen. Concentrations of testosterone, cortisol, and beta-endorphin were quantified. Behavior of the boars was recorded during exposure to the ArtSow and for 30 min after return to their home pen. Relative to preexposure levels, serum cortisol increased (P<.05) during CTRL exposure and after exposure to both treatments (CTRL; P<.04 and FRUS; P<.06). Serum testosterone did not change during and after either treatment. Serum concentrations of beta-endorphin did not change during or after CTRL trials, but serum beta-endorphin was greater (P<.05) during FRUS than during CTRL trials. Behavioral analysis revealed that boars spent less time lying down and more time moving about their home pen (P<.05) after a FRUS than after a CTRL trial. In summary, serum cortisol did not allow us to distinguish between the excitement of copulation and the negative affect associated with sexual frustration, whereas increases in serum beta-endorphin and motor activity seemed to be indicators of the negative emotional state of sexual frustration in trained boars.

cDNA sequence and expression of bovine prodynorphin.

Prodynorphin (ProDYN) in the anterior pituitary gland appears to be processed differently from the brain, and the ProDYN-derived peptides may function differently in the anterior pituitary than in the brain. To further investigate the roles of ProDYN-derived peptides in the anterior pituitary, we have determined the nucleotide (nt) sequence of the cDNA encoding bovine ProDYN. This is the first time a complete cDNA sequence for ProDYN has been reported. The nt and deduced amino acid (aa) sequences were compared to the known ProDYN of other species. Northern blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) combined with Southern blot analysis demonstrated that the expression of ProDYN in both the anterior and posterior pituitary glands was much lower than that in the neural tissues of the striatum and hypothalamus.

Expression of luteinizing hormone-releasing hormone and its receptor in porcine immune tissues.

Luteinizing hormone-releasing hormone (LHRH) is the primary regulator of pituitary LH release. However, LHRH has also been identified in extrahypothalamic sites including immune tissues. Accordingly, immunomodulatory properties for LHRH have been suggested. We wanted to determine whether LHRH and its receptor are produced by immune tissues in the pig. First, a cDNA was cloned and sequenced from the porcine hypothalamus that showed 87.5% homology with the human LHRH gene. Internal primers were identified from this sequence for amplifying a 268 bp product by PCR. In addition to the hypothalamus, PCR products reflecting LHRH mRNA were amplified in porcine spleen, thymus, and peripheral blood lymphocyte (PBL) cDNA. LHRH mRNA was not detected in liver, cerebral cortex, or pituitary tissue samples. Primers were designed to amplify a 360 bp fragment of LHRH-receptor cDNA. PCR products reflecting LHRH-receptor mRNA were amplified in pig hypothalamus, pituitary, thymus, spleen and PBL cDNA samples. No such products were amplified in cortex and liver samples. In summary, we report the sequence of a cDNA coding for LHRH and Gonadotropin-RH associated peptide (GAP) in the pig hypothalamus. Additionally, we provide evidence that LHRH and its receptor are synthesized in porcine immune tissues. This leads us to speculate that LHRH may have local, immunomodulatory functions in pigs.

Estrogen regulation of gonadotropin-releasing hormone receptor messenger RNA in female rat pituitary tissue.

Gonadotropin releasing hormone (GnRH) is crucial in regulating the reproductive system of female vertebrates. In the present study we have analyzed the estrogen regulation of the GnRH receptor mRNA at the cellular level in Sprague-Dawley female rats. Northern blot analysis detected 3 species (5.0, 4.5 and 1.4 kb) of GnRH receptor mRNA in pituitary tissues. The GnRH receptor mRNA levels of these 3 species were increased by estrogen. By in situ hybridization we observed a 3.5-fold increase in GnRH receptor mRNA levels after 48 h of estrogen treatment when compared to ovariectomized (OVX) rats, 12 h of estrogen treatment did not change the GnRH mRNA levels. Similar increases in GnRH receptor mRNA levels by estrogen were also found in Wistar-Imamichi female rat pituitary tissue. In situ hybridization analysis identified clusters of anterior pituitary cells that expressed the GnRH receptor mRNA. The estradiol effect depends on increased mRNA levels in these clusters. Moreover, a significant increase in the number of pituitary cells that expressed GnRH receptor was observed after 48 h of estrogen treatment. These findings suggest that the mechanisms for estrogen regulation of GnRH receptor include changing levels of GnRH receptor mRNA in the rat pituitary.

Luteinizing hormone-releasing hormone receptor messenger ribonucleic acid expression in the rat pituitary during lactation and the estrous cycle.

To study mechanisms underlying the modulation of luteinizing hormone-releasing hormone receptor (LHRH-R) during lactation and the estrous cycle, we used a reverse transcriptase-polymerase chain reaction (RT-PCR) procedure to generate a probe for rat LHRH-R messenger RNA (mRNA). Using primers based on the mouse sequence, we amplified an approximately 300 bp fragment from rat pituitary complementary DNA. This PCR product was shown to be part of LHRH-R cDNA by direct sequencing and by comparing to the rat LHRH-R cDNA reported recently. Then, this PCR fragment was used as a probe for northern blotting analysis. The level of LHRH-R mRNA in the pituitary was significantly decreased during lactation, by approximately 80%, compared to that of ovariectomized and intact (diestrous and metestrous cycling) rats while no statistical difference in glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) mRNA level was observed between groups. During the estrous cycle, the level of LHRH-R mRNA in the pituitary was about two-fold higher on diestrous day 2 and the morning of proestrus than that on diestrous day 1 and quickly returned toward control level by noon of proestrus. In addition, we found that GAPDH mRNA levels from a so-called housekeeping gene often thought to be unchanged under different conditions, were significantly higher on proestrus while levels of 18S rRNA were not significantly changed. The large decrease in LHRH-R mRNA during lactation could account for the changes in LHRH binding previously reported.

Disruption of estrous cyclicity following administration of a luteinizing hormone-releasing hormone antagonist to the preoptic area of the rat.

Experiments were designed to test the hypothesis that LHRH receptors in the preoptic area (POA) are of physiological importance for maintaining estrous cyclicity in the rat. Bilateral cannulae were implanted just dorsal to the POA. Estrous cycles were monitored daily by vaginal smears. Antide, a long-acting LHRH antagonist, was infused bilaterally (2.5 micrograms/side) in the POA or the hypothalamus on the mornings of diestrus I and II. As controls, at separate times, rats also received similar infusions of either vehicle (1:1 water:propylene glycol) or a bombesin antagonist (#B0650; Sigma, St. Louis, MO). Collection of daily vaginal smears continued, and the number of days from the first infusion to the next day of estrus that preceded a normal cycle was recorded. After infusion of Antide into the POA, rats demonstrated varying durations of interrupted cycles ranging from 11 days to more than 100 days. These periods of disruption were characterized by either long periods of diestrus, long periods of estrus, or an extended period of diestrus followed by an extended period of estrus. After infusion of Antide into the dorsomedial, ventromedial, or anterior hypothalamic areas, rats had either a 4- or 5-day estrous cycle and continued to cycle normally. Likewise, infusions into the septum had no effect. Infusion of vehicle or bombesin antagonist into any of the hypothalamic or POA sites tested also resulted in no interruptions in the cyclic activity of the rats. Therefore, it appears that functional LHRH receptors in the POA are necessary to drive the normal estrous cycle.

Luteinizing hormone-releasing hormone gene expression in the bovine brain: anatomical localization and regulation by ovarian state.

Experiments were conducted to identify neurons in the bovine brain that express the LHRH gene and to determine whether LHRH mRNA levels are influenced by the ovaries. Two groups of postpubertal heifers were utilized: heifers killed during the mid-luteal phase of the estrous cycle (LUTEAL, n = 5) and heifers killed 14-16 wk following ovariectomy (OVX, n = 5). In situ hybridization was performed through use of a 32P-end-labeled deoxyoligonucleotide (59 mer) complementary to the human LHRH mRNA sequence. LHRH-expressing neurons were identified in the diagonal band of Broca, the preoptic area, and the anterior hypothalamus in a manner consistent with immunocytochemical localization. Reduced silver grains, proportional to LHRH mRNA content, were quantified (in pixels, 45x objective) with an image analysis system. Expected serum hormone concentration differences between endocrine states were confirmed by radioimmunoassay for progesterone (LUTEAL > OVX, p < 0.01) and for LH (OVX > LUTEAL, p < 0.01). Compared to the OVX group, LUTEAL heifers had 34% fewer LHRH-expressing neurons (p < 0.05); on the average, these neurons possessed 28% fewer pixels/cell (p < 0.01), indicating fewer copies of LHRH mRNA per cell. When the numbers of pixels in all labeled cells were totalled, LUTEAL animals had 57% fewer pixels (p < 0.05) than did the OVX females--probably reflecting a decrease in LHRH synthetic capacity in the LUTEAL animals. Therefore, during the mid-luteal phase of the bovine estrous cycle, ovarian steroid (i.e., luteal progesterone) suppression of LHRH release (as reflected by serum LH) is coincident with decreased LHRH mRNA in the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha 1 adrenergic regulation of estrogen-induced increases in luteinizing hormone-releasing hormone mRNA levels and release.

Prazosin, an alpha 1 adrenergic antagonist, was used to examine the relationship between adrenergic inputs and the stimulatory effects of estrogen on LHRH mRNA and release. Bilateral cannulae were implanted just dorsal to the preoptic area (POA). Estrous cycles were monitored daily by vaginal smears. On the morning of diestrus, each rat was ovariectomized and assigned to one of three treatment groups: Control--injected with sesame oil (n = 5); Surge--injected with estradiol benzoate (EB, 10 micrograms) to produce an LH surge (n = 5); or, Surge+Prazosin--injected with EB and a prazosin-filled inner cannula was put into the POA (n = 6). Between 4-6 pm of the following day, rats were anesthetized, decapitated, trunk blood collected, and brains were stored in liquid nitrogen. In situ hybridization was performed using a 32P end-labelled 59-mer complementary to LHRH mRNA. Reduced silver grains, proportional to LHRH mRNA content, were quantified. Treatment with estrogen alone resulted in an LH surge and a 50% increase (P < 0.05) in numbers of cells expressing LHRH. This estrogen-induced increase and the LH surge were completely blocked (P < 0.01) by prazosin. Prazosin also decreased (P < 0.01) the median number of grains per cell from 81 (Surge) to 65 grains per cell (Surge+Prazosin). When the number of grains in LHRH-expressing neurons were totalled, EB increased (P < 0.05) LHRH gene expression by 53%, and local administration of prazosin completely blocked (P < 0.01) this increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha 1-adrenergic agonists act on the ventromedial hypothalamus to cause neuronal excitation and lordosis facilitation: electrophysiological and behavioral evidence.

To see if activation of central alpha 1-adrenergic receptors can cause facilitation of lordosis in rats, the behavioral effects of centrally administered alpha 1-agonists, methoxamine (MA) and phenylephrine (PhE), and related agents were studied. In ovariectomized rats treated with estrogen, infusion of MA, PhE, or a beta-agonist isoproterenol, into the lateral ventricle, or bilateral infusions of MA or PhE into the ventromedial hypothalamus (VMH) facilitated lordosis. Conversely, intra-VMH infusion of the alpha 1-antagonist prazosin (PZ) inhibited lordosis. Intra-VMH infusion of isoproterenol or an alpha 2-agonist clonidine, had no effect. Neither was the intra-VMH infusion of MA effective if: (i) the rats were not primed with estrogen; (ii) the tips of the cannulae were outside the VMH; or (iii) it was preceded by an intra-VMH infusion of the alpha 1b-antagonist, chloroethylclonidine (CEC). These results not only verify implications from recent studies that alpha 1-receptors in the hypothalamus are important for lordosis facilitation, but further show that the adrenergic facilitatory effect are: (i) mediated specifically by alpha 1b-subtype of the alpha 1-receptor, (ii) estrogen-dependent, and (iii) site-specific to VMH. To investigate neural mechanisms potentially underlying the lordosis-facilitating effect of alpha 1-activation, the actions of MA and PhE on the electrical activity of single neurons of the ventromedial nucleus of the hypothalamus (VMN) in vitro were studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential regulation of luteinizing hormone-releasing hormone and galanin messenger ribonucleic Acid levels by alpha(1) adrenergic agents in the ovariectomized rat.

α(1) -Adrenergic control of luteinizing hormone-releasing hormone (LHRH) and galanin mRNA levels was examined in ovariectomized rats. Each rat was ovariectomized and a permanent bilateral cannula was implanted 1 mm dorsal to the preoptic area. Eleven to 14 days later, each rat received one of three treatments: prazosin (α(1) antagonist, n = 8), methoxamine (α(1) agonist, n = 5) or control (no drug, n = 7). Each drug was suspended in a polyacrylamide gel matrix and delivered to the preoptic area via the bilateral cannula. After 24 h of continuous exposure to the adrenergic agents (or control), rats were anesthetized, decapitated and brains were stored in liquid nitrogen until sectioned (7 µm) on a cryostat. In situ hybridization was performed using a [(32) P]-end-labelled 59mer complementary to LHRH mRNA. Reduced silver grains, proportional to LHRH mRNA content, were quantified for number of LHRH cells per section, number of grains per labelled cell and total number of grains in labelled cells. Compared to the controls, prazosin caused a 32% decrease (P<0.05) in the number of cells expressing the LHRH gene. The LHRH cells from untreated animals had a median of 53 grains/cell with a smooth distribution above and below the median. Treatment with prazosin reduced the median number of grains/cell to 36 (P<0.05). When the number of grains in labelled cells were totalled, prazosin decreased (P<0.01) the number of grains by 47%. Surprisingly, methoxamine caused no quantitative changes in any of the parameters examined. This might be explained if LHRH transcription in control animals was proceeding at near-maximal rates supported, in part, by an endogenous α(1) ligand. Alternatively, continuous exposure to this agonist may have resulted in desensitization to its stimulatory effects. When anatomically matched brain tissue sections from these animals were examined for galanin mRNA, no differences among experimental groups were detected. In conclusion, administration of an α(1) -adrenergic antagonist into the preoptic area suppressed levels of LHRH mRNA but not galanin mRNA. Therefore, the data suggest that an endogenous α(1) ligand, such as norepinephrine (or epinephrine), is required to maintain a high level of LHRH gene expression in the ovariectomized rat.

Intracerebral immunoneutralization of beta-endorphin and met-enkephalin disinhibits release of pituitary luteinizing hormone in sheep.

Experiments were conducted to determine if endogenously produced beta-endorphin and met-enkephalin exert a physiological inhibition on luteinizing hormone-releasing hormone (LHRH) release in the central nervous system of sheep. Twenty-two mature ewes were implanted with unilateral guide tubes, through which matched infusion cannulae could be inserted without discomfort once daily for intracerebral (i.c.) infusion of three anti-opioid treatments: naloxone (50 micrograms in 20 microliters), sheep antisheep beta-endorphin (ABE; 20 microliters of 1:25) or sheep anti-met-enkephalin (AME; 20 microliters of 1:25) and of two control treatments: nonimmune sheep serum (20 microliters of 1:25) or sheep antiporcine thyroglobulin (20 microliters of 1:25). To detect abrupt disinhibition of LHRH release by anti-opioid treatments, serum luteinizing hormone (LH) was quantified at 10-min intervals for 1-2 h before and after each i.c. infusion. Complete trials consisted of 3-4 different anti-opioid or control i.c. infusions once daily at a single site over a period of 2-3 days during the luteal phase of recurring estrous cycles. Results were statistically evaluated within each ewe since complete trials were replicated 2-5 times within each ewe and because no 2 ewes could have i.c. infusions in identical locations. Anatomical generalizations were possible when LH responses to anti-opioid treatments were similar for several ewes with i.c. infusion sites in comparable brain regions. However, it was not possible to make such generalizations when infusion sites were not comparable in other ewes.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific binding of naloxone to ovine brain tissue: comparison of brain regions and endocrine states.

Binding of [3H]naloxone ([3H]NAL) to brain membranes was quantified by Scatchard analysis using two methods of separating bound from free [3H]NAL. In the centrifugation method, membranes that were soluble at 1,000 x g, but sedimented at 20,000 x g, were incubated with [3H]NAL. For filtration, all membranes that sedimented at 20,000 x g were incubated and filtered through glass filter fibers. Nonspecific binding was estimated using greater than 500-fold excess of unlabeled naloxone (10(-6) M). Specific binding of [3H]NAL was used to generate linear multiple-point Scatchard plots, which indicated a single class of high-affinity sites. In Exp. 1, 10 ovariectomized (OVX) ewes were injected with estradiol-17 beta alone or in combination with progesterone. Compared with OVX controls, these hormonal treatments did not affect binding of [3H]NAL (centrifugation method) to combined hypothalamus (HYP) + preoptic (POA) tissues. In cyclic ewes (Exp. 2, filtration method), affinity constants (2.4 +/- .2 x 10(8) M-1) did not differ among HYP, POA and basal forebrain (BF) tissues, but BF had more sites (39 +/- 3 fmol/mg) than either HYP (14 +/- 1) or POA (17 +/- 1). Binding affinity and concentration of sites within each brain area (HYP, POA, BF) did not differ between d 8 and d 16 (preovulatory but after luteolysis) in normally cycling ewes. Overall, neural tissue dissected from BF had a greater concentration of binding sites than HYP or POA. Exogenous and endogenous fluctuations in ovarian steroids did not affect binding of [3H]NAL to these tissues.

Biological activity of LH during the peripartum period and the estrous cycle of the ewe.

Biological activity of luteinizing hormone (LH) is related to the degree of glycosylation of the glycoprotein hormone. The objectives of this study were to determine changes in biologically (BLH) and immunologically (ILH) active LH concentrations in plasma (in vitro bioassay and radioimmunoassay, respectively) and in the ratio of BLH to ILH (B:I) during the peripartum period and during the estrous cycle of the ewe. Blood samples were collected daily 4 days before through 4 days after parturition and during one estrous cycle. Also, samples were collected at 15-min intervals for 6 hr on Days 3 and 12 of the estrous cycle to quantify the influence of an elevated plasma concentration of progesterone (P) on the episodic secretion profiles of BLH. Progesterone concentration was determined on the 4th days pre- and post-partum, on each day of the estrous cycle and at hourly intervals on Days 3 and 12 of the cycle to investigate the hypothesis of an inverse relationship between P and BLH. The BLH and ILH concentrations were low during the peripartum period, and the B:I ratio did not increase by the 4th day postpartum. Mean ILH concentration was greater (P less than .05) in the postpartum than during the prepartum period. During the estrous cycle, mean daily B:I ratio was consistently above unity except for the day of estrus. The pre-ovulatory LH surge (BLH and ILH) was associated with a decrease (P less than .05) in the mean B:I ratio to 0.0065. Mean concentrations of BLH and ILH in plasma samples collected every 15 min on Day 12 were similar to Day 3 of the cycle.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological activity of luteinizing hormone in the peripartum cow: least activity at parturition with an increase throughout the postpartum interval.

The biological (B) and immunological (I) activities of luteinizing hormone (LH) were determined during four peripartum periods in the cow. The sampling periods were PRE-5 (approximately 5 days prior to parturition), POST-3 (Day 2 or 3 postpartum), POST-12 (Day 11 or 12 postpartum) and LUTEAL (Day 11 or 12 following the first observed postpartum estrus). Blood samples were collected at 10-min intervals for either 8 h (PRE-5, POST-3, and POST-12) or 6 h (LUTEAL). Four hours prior to the end of each sampling period, 100 micrograms of luteinizing hormone-releasing hormone (LHRH) was injected i.v. Plasma concentrations of LH were analyzed by a validated bioassay (rat interstitial cell testosterone) and a radioimmunoassay. Area under the LHRH-induced LH release curve was calculated by the trapezoidal rule, and endogenous LH was determined by averaging the pre-LHRH treatment values. Paired t-analyses were used to compare LH release between periods. The periods of lowest (p less than 0.05) bioactive LH (BLH) were PRE-5 and POST-3. During POST-12, BLH was maximal. Endogenous immunoactive LH (ILH) was maximal during the POST-12 period, with PRE-5, POST-3, and LUTEAL being the least (p less than 0.05). The B:I ratio was lowest (p less than 0.05) around the time of parturition (PRE-5 and POST-3), then increased (p less than 0.05) by Day 12 postpartum. The ratio then increased (p less than 0.05) again by the LUTEAL period. These data suggest that the biological quality of LH changes throughout the puerperium. We infer from these data that the low biological activity of LH (subquality LH) may contribute to the postpartum infertility in the cow.