Stress- as well as suckling-induced prolactin release is blocked by a structural analogue of the putative hypophysiotrophic prolactin-releasing factor, salsolinol.

Prolactin is secreted from the anterior lobe of the pituitary gland in response both to suckling and to stress. We recently observed that 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), produced in the neurointermediate lobe of the pituitary gland, as well as in the medial basal hypothalamus, can selectively release prolactin from the anterior pituitary. Therefore, it has been proposed that salsolinol is a putative endogenous prolactin-releasing factor (PRF). Here, we report that one structural analogue of salsolinol, 1-methyl-3,4-dihydroisoquinoline (1MeDIQ), can block salsolinol-induced release of prolactin, but does not affect prolactin release in response to thyrotropin releasing hormone (TRH), alpha-methyl-p-tyrosine (alpha MpT) (an inhibitor of tyrosine hydroxylase), domperidone (a D(2) dopamine receptor antagonist), or 5-hydroxytryptophan (5-HTP), a precursor of serotonin). 1MeDIQ profoundly inhibited suckling-, immobilization-, as well as formalin-stress induced prolactin release without any influence on corticosterone secretion. The 1MeDIQ-induced reduction in prolactin response to immobilization stress was dose-dependent. These results suggest that salsolinol can play a pivotal role in the regulation of prolactin release induced by either physiological (suckling) or environmental (stress) stimuli.

Somatostatina y cáncer de próstata / Somatostatin and prostate cancer

Cada vez es más evidente que la estructura y función prostática no dependen solamente de andrógenos. Actualmente, se admite que en los trastornos de la proliferación prostática están también implicadas hormonas peptídicas, factores de crecimiento, bucles reguladores autocrinos/paracrinos e interacciones entre el epitelio y el estroma. En este sentido, las células neuroendocrinas han despertado un enorme interés, debido en parte a la relación existente en el cáncer de próstata entre diferenciación neuroendocrina y progresión del tumor. Entre los factores sintetizados y liberados por las células NE se encuentra la somatostatina. Este neuropéptido y sus análogos presentan actividad antineoplásica en gran variedad de modelos experimentales tanto in vitro como in vivo.El efecto antiproliferativo de la somatostatina puede ser indirecto, dada la capacidad de la SS de inhibir la secreción de hormonas tróficas y factores de crecimiento, o directo a través de los receptores presentes en las propias células normales y tumorales. Los análogos de somatostatina han demostrado su eficacia en tumores prostáticos experimentales inducidos en animales, sin embargo los resultados obtenidos en los ensayos clínicos son contradictorios. Aunque la somatostatina y sus análogos son capaces de inhibir la liberación de la prolactina y de la hormona del crecimiento, estudios in vivo e in vitro sugieren que la somatostatina pueda actuar directamente sobre el crecimiento del tumor. En este sentido, aunque es evidente que la próstata tiene receptores para somatostatina, los resultados obtenidos sobre su distribución, los subtipos expresados y su relación con diferentes situaciones patológicas son contradictorios e insuficientes. Por lo tanto, es de esperar que un mejor conocimiento de los mecanismos celulares implicados en el efecto aritiproliferativo de la somatostatina ayude a diseñar nuevos análogos específicos que permitan realizar nuevos ensayos clínicos y valorar con exactitud la eficacia de la somatostatina en el tratamiento del cáncer de próstata. (AU)

Inhibición de la lactancia con lis rida: evaluación clínica / Lactation inhibition with lisuride clinical evaluation

El fenómeno de lactancia en la especie humana obedece a un complicado mecanismo neuro-endocrino. Durante el embarazo, el papel de los estrógenos y la progesterona es determinante y en el posparto inmediato, la presencia de insulina, cortisol, tiroxina, hormona del crecimiento y lactógeno placentario son indispensables para la completa expresión de la acción lactogénica de la prolactina. En un estudio lineal, prospectivo, simple y abierto, 50 mujeres primigestas o multigestas, entre 19 y 30 años de edad, con parto vaginal o cesárea y con gestaciones entre 34 y 41 semanas, se les administró lisurida como inhibidor de la lactancia, a dosis de 0.2 mg cada 8 horas, por vía oral, durante 14 días. Todas las pacientes tenían indicación médica para inhibir la lactancia y la medicación se inició en el posparto inmediato, con supresión de la succión mamaria, con restricción líquida durante 24 horas y con vendaje mamario compresivo. La evaluación de los efectos se hizo a la 24 horas y a los 14 días del parto o la cesárea anotando los datos mamarios de forma, volumen, simetría, coloración, estado de la superficie, temperatura, turgencia, consistencia, presencia de red venosa, estado de los pezones, presencia de calostro y crecimiento de los ganglios vecinos. La inhibición de la lactancia que ya se había iniciado a las 24 horas en el 87 por ciento de las pacientes, fue excelente. Los fenómenos inflamatorios y el dolor fueron mínimos y a las 2 semanas la involución fue muy evidente. En ninguna hubo lactancia de rebote. 5 pacientes tuvieron náusea leve y pasajera al inicio del tratamiento y en 6 hubo adenomegalia dolorosa. Creemos que la lisurida constituye una opción recomendable para inhibir la lactancia suprimiendo los molestos síntomas del dolor y la ingurgitación mamaria-y sin los efectos indeseables de la hormonoterapia

Prolactin release from perifused human decidual explants; effects of decidual prolactin-releasing factor (PRL-RF) and prolactin release-inhibitory factor (PRL-IF).

The dynamics of prolactin release from human decidual explants were studied under basal conditions, in response to decidual prolactin-releasing factor (PRL-RF), and in response to PRL-RF in the presence of decidual prolactin release-inhibitory factor (PRL-IF) or other factors known to inhibit prolactin release in static cultures. Explants were perifused with medium at a rate of 6 ml/h, and the medium was collected at 5 min intervals. The explants released prolactin for up to 20 h without evidence of cell necrosis, with the rate of prolactin decreasing gradually from 3.9 +/- 0.1 ng/5 min during the first 2 h to 2.2 +/- 0.1 ng/5 min during the last 2 h of exposure. PRL-RF, a 23.5 KMr protein released by the placenta, stimulated a dose-dependent increase in prolactin release from the perifused explants that occurred within the first 5 min of exposure and persisted until the exposure to the releasing factor was discontinued. PRL-IF, a 35-45 K Mr protein released by the decidua, caused a dose-dependent inhibition of PRL-RF-mediated prolactin release. Dibutyryl cAMP, cholera toxin, sn-1, 2-dioctonylglycerol, PMA, and arachidonic acid, which inhibit basal prolactin release from static decidual cultures, also caused a dose-dependent inhibition of prolactin release in response to PRL-RF. In each instance, the maximal dose of the agents tested inhibited PRL-RF-mediated prolactin release by greater than 84 per cent. These results indicate that the stimulation of prolactin by PRL-RF is inhibited by PRL-IF and pharmacologic agents that inhibit basal prolactin release.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphine can stimulate prolactin release independent of a dopaminergic mechanism.

Prolactin release is controlled by prolactin-release inhibiting factor (PIF), possibly dopamine, and an unidentified putative hypothalamic prolactin-releasing factor (PRF). Morphine and related opioids may indirectly stimulate prolactin release by inhibiting PIF release and (or) by stimulating putative PRF release. In the present study, we have completely blocked the dopaminergic receptors in normal male rats by pretreatment with a large dose of pimozide (3 mg/kg) to demonstrate if putative PRF has a role in morphine-induced prolactin release. Morphine sulfate (10 mg/kg) was still able to stimulate prolactin release in the rat without any functional dopaminergic PIF receptors. When naloxone (3 mg/kg) was injected 20 min before the morphine in the pimozide-treated rat, plasma prolactin concentration was not affected by morphine indicating that the stimulatory effect of this opioid on prolactin release in the pimozide-pretreated rat was mediated by mu-receptors. We can conclude that morphine can stimulate prolactin release through a mechanism apparently independent of dopaminergic receptors, one possible route being through a putative PRF.

Purification of a non-dopaminergic and non-GABAergic prolactin release-inhibiting factor (PIF) in sheep stalk-median eminence.

Prolactin release-inhibiting factor (PIF) extracted from 1200 sheep stalk-median eminences was purified by gel filtration on a Sephadex G-25 column (4.5 X 150 cm). PIF activity was determined by measuring the inhibition of prolactin release from dispersed anterior pituitary cells of adult male or estrogen-primed, ovariectomized rats. Using this system, PIF was detected in tube fractions 122-127 (volume = 20 ml/tube). These fractions also contained LHRH and somatostatin; however, these peptides had no prolactin-inhibiting activity in the quantities present. No dopamine or gamma-aminobutyric acid (GABA) was detected in the active fractions by radioenzymatic assay and fluorophotoenzymatic assay, respectively. Furthermore, receptor blockers for dopamine or GABA did not interfere with the PIF activity. These findings indicate that the PIF activity cannot be attributed to either dopamine or GABA, both of which are known to inhibit prolactin release, and provide evidence for the presence of a non-dopaminergic and non-GABAergic PIF within the hypothalamus.

Steroid receptor levels in intact and ovariectomized estrogen-treated rats: an examination of quantitative, temporal and endocrine factors influencing the efficacy of an estradiol stimulus.

Cell nuclear estrogen receptors and cytosol progestin receptors were measured in the pituitary gland, preoptic area and hypothalamus throughout the estrous cycle of the rat. Cell nuclear estrogen receptor levels paralleled changes in serum estradiol concentrations with highest values on proestrus and lowest on diestrus. Proestrous values were 50-60% of capacity for each tissue. Cytosol progestin receptor number in these tissues was also highest on proestrus and lowest on diestrus. With these data as a guide, Silastic capsules filled with estradiol-cholesterol mixtures were used to generate physiologic levels of estrogen receptor occupation within the brain-pituitary complex of ovariectomized rats and to examine the kinetics of estradiol stimulation of lordosis behavior and cyclic gonadotropin release. Our results indicate that the effectiveness of an estradiol stimulus to elicit lordosis or luteinizing hormone release depends on at least three factors: the magnitude of the increment in serum estradiol and brain and pituitary cell nuclear estradiol receptor levels; the duration over which these increments area maintained; and the interval from previous exposure to estrogen.

Dopamine, PIF, and other regulators of prolactin secretion.

Considerable evidence now exists that dopamine is a physiological prolactin inhibiting factor (PIF); however, it may not represent the only PIF. Amphetamine, which releases newly synthesized dopamine and blocks prolactin release, caused an increased in dopamine levels in the pituitaryb gloand. Prolactin release appears to be regulated also by a prolactin releasing factor (PRF). A wide variety of hypothalamic peptides stimulate prolactin release, but only two of these (thyrotropin releasing hormone and vasoactive intestinal polypeptide) can act directly on the pituitary and thus are candidates for PRF.

Preliminary characterization of bovine pineal prolactin releasing (PPRF) and release-inhibiting factors (PPIF) activity.

Bovine pineal glands were subjected to extraction with dilute acetic acid, gel filtration on Sephadex G-25 and subsequent ultrafiltration through Diaflo membranes PM10, UM2 and UM05. Various fractions derived at each step were tested for the presence of substances which stimulate or inhibit prolactin secretion in vitro and in vivo. Both prolactin releasing (PPRF) and release-inhibiting (PPIF) activities were observed. PPRF activity was present in certain fractions derived from Sephadex G-25 and in the PM10 residue (MW congruent to less than 10,000). Whereas both the UM2 residue (MW greater than 1000) and UM05 filtrates (MW less than 500) was seen to inhibit pituitary prolactin release in vitro, the UM05 residue (MW greater than 500 and less than 1000) inhibited prolactin release in vivo, possibly by stimulating the secretion of the hypothalamic prolactin inhibiting factor. On the basis of its inactivation by trypsin it was concluded that PPIF may be a peptide or contain a peptide moiety indispensible for its biological activity. Experiments are in progress to characterize pineal prolactin-regulating activities and to elucidate further the physiological role of the pineal gland in the regulation of prolactin secretion.

Hormonal control of zinc uptake and binding in the rat dorsolateral prostate.

The zinc uptake in the dorsolateral prostate of rats was studied after different hormonal manipulations. Orchiectomy reduced the uptake of 65Zn. Administration of estradiol benzoate to orchiectomized rats doubled the 65Zn uptake, a phenomenon which was not observed in orchiectomized-adrenalectomized rats. Adrenalectomy in orchiectomized rats had no effect on the concentration of radioactivity beyond the castration-induced decrease. A prolactin release inhibitor, 6-methyl-8-erogelenylacetamide, reduced the radioactivity concentration without changing the weight of the gland. Cyproterone acetate reduced the weight but not the radioactivity concentration. The concentration of 65Zn in the ventral prostate was not changed by orchiectomy, adrenalectomy, or the administration of estradiol benzoate, prolactin release inhibiors, or cyproterone acetate. The results suggest an important role for prolactin in the zinc uptake in the dorsolateral prostate but not in the ventral prostate.

Some new approaches to potential test systems for drugs against prostatic cancer.

We have previously reported on test systems, based on 5alpha-reductase (5alpha-RA) and arginase activities and steroid deposition in animal prostates, potentially useful in screening drugs possibly effective in cancer of the prostate. Recently, we have concentrated on the development of other in vivo and in vitro systems which may prove of further value in testing such drugs. These systems include the following: (a) The effects of drugs on 5alpha-RA activity in human and animal non-malignant and human cancerous prostatic tissues in organ culture. The parameters necessary for the maintenance of optimal 5alpha-RA in such explants have been determined, and it has been shown that certain agents (estramustine phosphate, progesterone, estradiol-17beta) can inhibit 5alpha-RA under in vitro conditions, pointing to the potential use of such an approach in screening various cytostatic agents. In addition, 65Zn deposition, the histology, and the androgen metabolism in such tissues in organ culture are being determined as additional parameters. (b) The deposition of 65Zn in the rat dorsolateral gland, particularly as affected by prolactin and testosterone, and the effects of chemotherapeutic agents on such deposition. Methotrexate and CCNU have been shown to be potent inhibitors of 65Zn deposition in the dorsolateral gland. The parameters related to zinc metabolism in the prostate are being further investigated. (c) The demonstration of receptors for estrogens (estradiol-17beta, diethylstilbestrol) in the prostate of the baboon. The various parameters related to the specificity of such receptors have been established. The development and standardization of these approaches, some facets of which are reported in the present publication, may prove them to be more sensitive, specific, and optimal than other systems and should afford an opportunity to test various combinations of drugs potentially useful in cancer of the prostate with relative speed, efficacy, and ease of manipulation.

Evaluation of research on control of prolactin secretion.

At least three substances have been reported to be present in the hypothalamus that can inhibit prolactin release, namely a PIF, catecholamines and acetylcholine. At least four substances have been reported to be present in the hypothalamus that can stimulate prolactin release, namely PRF, TRH, serotonin and prostaglandins. Neither the existence of a distinctive PIF or PRF in the hypothalamus can be considered as definitely established. The predominant action of the mammalian hypothalamus on prolactin release is inhibitory under most conditions, and is stimulatory in avian species. In addition to control by the hypothalamus, several hormones and drugs can act directly on the pituitary to alter prolactin release. The interrelationships of these agents within and without the hypothalamus on prolactin secretion are complex, and there are many questions about their mode of action. Studies on the regulation of prolactin secretion have resulted in development of many methods for either increasing or decreasing release of this important hormone, and thereby have provided opportunities for influencing lactation, growth of mammary and pituitary tumors and other tissues responsive to prolactin.

Prolactin release inhibiting and stimulating factors in the hypothalamus.

Catecholamines, especially norepinephrine and dopamine, as well as GABA extracted from porcine hypothalamic tissue, were found to possess PIF activity in vitro. However, more work is needed to determine whether or not the effects of GABA or catecholamines on prolactin release are physiological or pharmacological. Until such studies are completed and until the chemical nature and biological roles of other substances with PIF activity found in the hypothalamus are clarified, no conclusion as to the nature of the physiological inhibitor of prolactin release should be made.

Extraction and partial purification of prolactin-release stimulating factor in bovine hypothalami.

Partial purification of prolactin-release stimulating factor (PRF) was performed by Sephadex G-25 gel filtration of bovine hypothalamic extracts. PRF activity was evaluated on the basis of the measurement of immunoreactive prolactin released from the isolated rat hemipituitary in vitro. PRF activity was found in the fractions with Kav=0-0.49 and prolactin-release inhibiting activity was also detected in the fractions with Kav=0.69-0.89. The dose-response relationship was established between the partially purified PRF and its activity. The elution position of the partially purified PRF preceded that of TRH on Sephadex G-25. TRH at the dose of 100 nM stimulated the release of TSH in vitro, but not the release of prolactin. These results may indicate that there exists PRF with a relatively high molecular weight in the bovine hypothalamus.