Hyperprolactinemia and estrogen-induced rhythms in LH and prolactin release in the ovariectomized rat

Summary Short-term (9 days) hyperprolactinemia induced by pituitary grafts reduced basal plasma LH levels in ovariectomized rats whereas long-term (31 days) grafts increased basal LH levels. Although long-term grafts inhibited estradiol-induced prolactin surges, hyperprolactinemia had no effect on the LH surge. It is concluded that the estrogen-treated ovariectomized rat is not suitable for studying the effects of hyperprolactinemia on LH release.     

Lesions in suprachiasmatic nuclei simulate effects of pinealectomy on prolactin release in ovariectomized and sulpiride-treated female rats

Summary Previous studies indicate that the pineal gland alters prolactin secretion, and it was suggested that at least part of the effect of the pineal hormone melatonin on prolactin release may be mediated by the hypothalamic structures. In this study, pinealectomy and lesions of the suprachiasmatic nuclei were found to alter serum levels of prolactin in the same direction, an effect that was counteracted by daily afternoon melatonin administration. Melatonin, but not other pineal indoles, also prevented sulpiride-induced prolactin secretion in pinealectomized or suprachiasmatic nuclei-lesioned and ovariectomized rats, which suggested that the pineal gland can modulate prolactin secretion by acting through a dopamine mechanism independent of hypothalamic suprachiasmatic structures.The authors thank Ms Karen Shashok for revising the English style. This work was supported in part by a grant GG85-0168 from the Comisión Asesora de Investigación Cientifica y Ténica. The NIAMDD, through the National Pituitary Agency, supplied the radioimmunoassay materials for prolactin determinations.     

Lesions in suprachiasmatic nuclei simulate effects of pinealectomy on prolactin release in ovariectomized and sulpiride-treated female rats

Previous studies indicate that the pineal gland alters prolactin secretion, and it was suggested that at least part of the effect of the pineal hormone melatonin on prolactin release may be mediated by the hypothalamic structures. In this study, pinealectomy and lesions of the suprachiasmatic nuclei were found to alter serum levels of prolactin in the same direction, an effect that was counteracted by daily afternoon melatonin administration. Melatonin, but not other pineal indoles, also prevented sulpiride-induced prolactin secretion in pinealectomized or suprachiasmatic nuclei-lesioned and ovariectomized rats, which suggested that the pineal gland can modulate prolactin secretion by acting through a dopamine mechanism independent of hypothalamic suprachiasmatic structures.     

Effects of progesterone implants in the mesencephalon of ovariectomized rats on LH and FSH release triggered by exogenous gonadal steroids

Unilateral implantation of crystalline progesterone into the caudal mesencephalic reticular formation (MRF) of chronically ovariectomized adult rats prevents the triggering effect of exogenous gonadal steroids on LH release and does not affect the release of FSH in the same animal.     

Effect of sulpiride on prolactin release by rat pituitaries in vitro

Résumé La sulpiride stimule la libération de la prolactine de l'hypophise après 4 h d'incubation. L'addition d'extraits hypothalamiques l'inhibe, mais la sulpiride ajoutée en même temps aux extraits hypothalamiques permet l'inversion de cet effet d'inhibition. Il semble evident que la sulpiride peut modifier la libération de la prolactine en agissant directement sur l'hypophise du rat, in vitro.     

Clomiphene citrate can mimic the augmentative (positive) but not the depressing (negative) effect of estradiol on the LHRH-stimulated release of LH and FSH by the pituitary gland of the long-term ovariectomized rat

In the long-term ovariectomized rat, both estradiol benzoate (EB) and clomiphene citrate enhance the release of LH induced by luteinizing hormone-releasing hormone (LHRH). EB also enhances the release of FSH. In rats pretreated with LHRH, EB strongly depresses the LHRH-induced LH/FSH release, but clomiphene enhances this release, regardless of the presence of EB.     

Clomiphene citrate can mimic the augmentative (positive) but not the depressing (negative) effect of estradiol on the LHRH-stimulated release of LH and FSH by the pituitary gland of the long-term ovariectomized rat

Summary In the long-term ovariectomized rat, both estradiol benzoate (EB) and clomiphene citrate enhance the release of LH induced by luteinizing hormone-releasing hormone (LHRH). EB also enhances the release of FSH. In rats pretreated with LHRH, EB strongly depresses the LHRH-induced LH/FSH release, but clomiphene enhances this release, regardless of the presence of EB.     

The influence of somatostatin on drug-induced prolactin release in the monkey

Summary The infusion of linear somatostatin did not block prolactin release induced by either perphenazine, TRH or serotonin. Somatostatin infusion, however, potentiated prolactin release induced by perphenazine and TRH but not that induced by serotonin.Supported in part by NIH General Research Support Grant No. RR5384 to Wayne State University School of Medicine and by NIH Research Grant No. HDO7722.The authors wish to express their appreciation to Mrs.Cynthia Van De Walle for her outstanding technical assistance in the performance of the prolactin RIA and the statistical analyses. We also appreciate receiving linear somatostatin from Dr.R. Makineni, Bachem Inc., Marina Del Ray, California, USA and from Dr.N. H. Grant, Wyeth Laboratories, Philadelphia, Pa. USA. We would like to thank Abbott Laboratories, North Chicago, Ill. USA for the gift of TRH and the Schering Corp., Bloomfield, N.J. USA for the gift of perphenazine.     

Effects of oestradiol and progesterone on FSH and LH contents of the pituitaries and blood of ovariectomized ewes

Zusammenfassung Zufuhr von 20 µg Östradiolbenzoat an zwei sich folgenden Tagen verursachte bei ovariektomierten Mutterschafen keine Veränderung im FSH- und LH-Gehalt von Hypophyse und Serum. Nach cinmaliger Verabreichung von 10 mg Progesteron (nach östradiolbehandlung) stieg das FSH im Blut an. Ebenso ergab Zufuhr von 20 mg Progesteron bei mit Östrogen behandelten Mutterschafen Anstieg des LH-Gehaltes im Blut.     

Peptide-stimulated release of prolactin from the fowl anterior pituitary gland

Summary Anterior pituitary glands from broiler fowl were preincubated for 24 h in either medium 199 only or medium containing estradiol 17, following which they were incubated in medium containing thyrotrophin releasing hormone (TRH), vasoactive intestinal polypeptide (VIP) or substance P (SP), alone or with the dopamine agonist, apomorphine. Estradiol priming stimulated release of prolactin and enhanced apomorphine-inhibition of prolactin release. TRH stimulated prolactin release, an effect reversed by apomorphine, and priming with estradiol potentiated both effects. VIP stimulated prolactin to a lesser degree and again this was inhibited by apomorphine and potentiated by estradiol. SP had little effect on the nonsteroid-primed pituitary, but stimulated release of prolactin after estradiol treatment, though less effectively than TRH or VIP.     

Hypothalamic tyrosine hydroxylase activity, plasma gonadotropin and prolactin levels after aminooxyacetic acid in ovariectomized rats

Plasma concentrations of gonadotropin, prolactin and hypothalamic tyrosine hydroxylase (TH) activity were measured in ovariectomized rats treated with aminooxyacetic acid (AOAA), a drug which elevates brain GABA levels. Hypothalamic TH activity was significantly increased with a significant decrease in prolactin (Prl) release. Plasma levels of gonadotropins were not modified by AOAA. These results support an inhibitory action of GABA on Prl release possibly mediated through hypothalamic dopamine.     

The effects of continuous chloroform and halothane anesthesia on plasma prolactin levels in ovariectomized estrogen-treated rats

Summary In ovariectomized, estrogen-treated rats bearing indwelling aortic catheters, continuous inhalation of chloroform or halothane resulted in increases in plasma prolactin levels 10 min after the exposure to the anesthetics. The plasma prolactin levels over the subsequent 2 h, however, were not significantly different from that of the control animals.Supported by NSF Research Grant BMS 74-17332.The authors wish to express their appreciation to Mrs Cynthia Van De Walle for her outstanding assistance in the performance of the prolactin RIA and the art work.     

Hypothalamic tyrosine hydroxylase activity,plasma gonadotropin and prolactin levels after aminooxyacetic acid in ovariectomized rats

Summary Plasma concentrations of gonadotropin, prolactin and hypothalamic tyrosine hydroxylase (TH) activity were measured in ovariectomized rats treated with aminooxyacetic acid (AOAA), a drug which elevates brain GABA levels. Hypothalamic TH activity was significantly increased with a significant decrease in prolactin (Prl) release. Plasma levels of gonadotropins were not modified by AOAA. These results support an inhibitory action of GABA on Prl release possibly mediated through hypothalamic dopamine.Supported by grants from Indian Council of Medical Research (ICMR), New Delhi. RIA kits for the estimation of LH, FSH and Prl were kindly supplied by Dr A.F. Parlow, NIAMDD-NIH, Bethesda, Maryland, USA. GNB is a UGC research fellow.     

Inhibitory effects of LHRH on LH receptors in the rat testis]

A single injection of LHRH to the adult male rat, as of its analog [D-Ala6, des-Gly-NH102] LHRH ethylamide, resulted in a marked decrease in LH receptors in the tests. Plasma testosterone level and the weight of the seminal vesicles and prostate were also decreased after treatment. These data demonstrate that LHRH can decrease the sensitivity of LH receptors and testicular function in the rat.     

Evidence that a 'critical period' is involved in early estrogen-induced LH- and FSH-release during the estrous cycle in the rat

LH- and FSH-release, which occurred in the afternoon of diestrus 1 following estradiol benzoate administration in the morning of estrus, was completely prevented by pentobarbital, when injected on diestrus 1 at 13.30 h.     

Ontogeny of the sex steroid and prolactin receptors in the male rat adrenal gland

Cytosolic estrogen and androgen receptors and membrane prolactin-binding sites in the male adrenal glands showed a definite pattern during sexual development. The level of sexual steroid receptors paralleled adrenal growth, whereas prolactin binding reached its maximum value in mature rats.     

Ontogeny of the sex steroid and prolactin receptors in the male rat adrenal gland

Summary Cytosolic estrogen and androgen receptors and membrane prolactin-binding sites in the male adrenal glands showed a definite pattern during sexual development. The level of sexual steroid receptors paralleled adrenal growth, whereas prolactin binding reached its maximum value in mature rats.Lüthy, I. A., Predoctoral Fellow from the Consejo Nacional de Investigaciones Cientificas y Técnicas and Calandra, R. S., Research Career Awardee from the Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina.Acknowledgments. We would like to thank Mrs D. Bas and Mrs D. B. Destéfano for the skillful technical assistance and the secretarial work, respectively. This work was partially supported by the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET), and the Comisión Nacional de Energía Atómica.