Béla Kanyicska

Endothelin-3 inhibits prolactin and stimulates LH, FSH and TSH secretion from pituitary cell culture

The influence of endothelin-3 (ET-3) on anterior pituitary hormone secretion was investigated over a wide range of concentrations (from 10(-14) to 10(-6) M) and incubation times (from 4 to 48 hours). ET-3 elicited a concentration-dependent inhibition of prolactin (PRL) secretion and stimulated the release of luteinizing hormone (LH), follicle stimulating hormone (FSH) and thyroid stimulating hormone (TSH) from primary monolayer cultures of anterior pituitary cells derived from female rats. The responsiveness of different pituitary cells to ET-3 differs markedly in terms of onset and duration: the maximal inhibition of PRL secretion occurred after 12 hours and the stimulation of LH, FSH and TSH reached the maximum after 4, 48 and 48 hours of incubation, respectively. These data corroborate the concept that ET-3 has an important role as a neuroendocrine modulator. Moreover, the data presented suggest different intracellular mechanisms underlying ET-3 actions.

Nuclear translocation of STAT5 and increased expression of Fos related antigens (FRAs) in hypothalamic dopaminergic neurons after prolactin administration

Ample evidence indicates feedback relationships between pituitary prolactin and hypothalamic dopaminergic neurons. Since the presence of prolactin receptors was earlier demonstrated in hypothalamic dopaminergic neurons, our working hypothesis was that prolactin induced activation of prolactin receptor coupled signaling leads to increased neuronal activity in these neurons. The aim of this study was to correlate prolactin receptor mediated signaling and prolactin induced activation in hypothalamic dopaminergic neurons. We used nuclear translocation of STAT5 as a marker of prolactin receptor induced signaling and expression of Fos related antigens (FRAs) as an indicator of neuronal activation. We performed double label immunocytochemical studies to determine the time course of the presence of FRAs and STAT5 in the nuclei of hypothalamic dopaminergic neurons after ovine prolactin treatment. Exogenous ovine prolactin treatment of ovariectomized rats resulted in an increase in serum ovine prolactin levels and a decrease in endogenous serum prolactin levels, indicating that ovine prolactin activated mechanisms inhibited pituitary prolactin secretion. Indeed, ovine prolactin activated the prolactin receptors in most subpopulations of hypothalamic dopaminergic neurons, resulting in nuclear translocation of STAT5. Also, increased neuronal activity, indicated by expression of FRAs, was observed in the same neuron populations after ovine prolactin treatment. These results suggest that signal transduction mechanisms coupled to prolactin receptors in hypothalamic dopaminergic neurons resemble those observed in other tissues; and nuclear translocation of STAT5 can be used as a marker of prolactin receptor activation in hypothalamic dopaminergic neurons.

Effects of reserpine and antidepressants on dopamine and DOPAC (3,4-dihydroxyphenylacetic) concentrations in the striatum, olfactory tubercle and median eminence of rats

The dopamine, noradrenaline and 3,4-dihydroxyphenylacetic acid (DOPAC) levels of various rat brain areas (median emience, olfactory tubercle, rostral and caudal part of the striatum) were measured. The effects of reserpine and antidepressants: amitriptyline, nomifensine and EGYT 475 (1-benzyl-4-/2-piridylcarbonyl/piperazine) were investigated. The dopamine content of the median eminence proved to be the most sensitive to the depletory effect of reserpine. Reserpine (1 mg/kg i.p.) caused a decrease of dopamine in the median eminence, in the olfactory tubercle and in the rostral striatum but not in the caudal striatum. Amitriptyline and EGYT 475 antagonized the reserpine-induced dopamine depletion in the olfactory tubercle. In the median eminence amitriptyline attenuated the effect of the depletor while nomifensine augmented it; EGYT 475 was without effect. The antidepressants antagonized the reserpine-induced increase of DOPAC in the rostral part of the striatum.

Endothelin is an autocrine regulator of prolactin secretion.

The aim of this study was to establish the cellular source of ET-like peptides affecting PRL secretion. Fluorescence double label immunocytochemistry and confocal laser scanning microscopy were used to demonstrate cellular colocalization for PRL and endothelin-1 (ET1)-like immunoreactivities in the anterior lobe of the pituitary gland of rats. An ET-specific reverse hemolytic plaque assay was applied to demonstrate that lactotrophs are capable of releasing ET-like peptides. A PRL-specific reverse hemolytic plaque assay was used to assess the influence of the released endogenous ETs on PRL secretion. ET(A)-specific receptor antagonists BQ123 and BQ610, and endothelin convertase enzyme inhibitory peptide, [22Val]big ET1-(16-38), increased PRL secretion, whereas the ET(B) receptor-specific antagonist BQ788 was ineffective. The ET(A) antagonist BQ123-induced increase in PRL secretion followed a bell-shaped dose-response curve in cells obtained from female rats, whereas it followed a sigmoid curve in males. Frequency distribution of PRL plaque sizes using logarithmically binned data revealed two subpopulations of lactotrophs with differential responsiveness to endogenous ETs. These data demonstrate that a large proportion of lactotrophs is capable of expressing and secreting ET-like peptides in biologically significant quantities. As low pituitary cell density in reverse hemolytic plaque assay minimizes cell to cell communications, these findings constitute direct proof of autocrine regulation of PRL secretion by ET-like peptides.The aim of this study was to establish the cellular source of ET-like peptides affecting PRL secretion. Fluorescence double label immunocytochemistry and confocal laser scanning microscopy were used to demonstrate cellular colocalization for PRL and endothelin-1 (ET1)-like immunoreactivities in the anterior lobe of the pituitary gland of rats. An ET-specific reverse hemolytic plaque assay was applied to demonstrate that lactotrophs are capable of releasing ET-like peptides. A PRL-specific reverse hemolytic plaque assay was used to assess the influence of the released endogenous ETs on PRL secretion. ETA-specific receptor antagonists BQ123 and BQ610, and endothelin convertase enzyme inhibitory peptide,[ 22Val]big ET1-(16–38), increased PRL secretion, whereas the ETB receptor-specific antagonist BQ788 was ineffective. The ETA antagonist BQ123-induced increase in PRL secretion followed a bell-shaped dose-response curve in cells obtained from female rats, whereas it followed a sigmoid curve in males. Frequenc...

Neonatal Treatment with Monosodium-L-Glutamate: Differential Effects on Growth Hormone and Prolactin Release Induced by Morphine

The aim of this study was to investigate further the possible role of nerve cells of the arcuate nucleus in the regulation of growth hormone (GH) and prolactin (PRL) secretion. Newborn male rats were treated with monosodium-L-glutamate (MSG) (4 g/kg body weight subcutaneously) or NaCl (0.5 g/kg) on alternate days for the first 10 days of life, and were used 8-9 weeks afterwards. beta-Endorphin-like immunoreactivity in the arcuate nucleus decreased by 54% after MSG treatment. The dopamine content of the median eminence was reduced to 55% of that in NaCl-treated litter mates. No significant change of dopamine content was found in the other hypothalamic regions examined. Basal levels of plasma PRL were unaltered. Intravenous injection of morphine to urethane-anesthetized animals was 3 times more potent in stimulating PRL secretion in MSG-treated rats, while it was 2.5 times less potent in releasing GH. These data suggest that lesioning of the arcuate nucleus by MSG treatment damages neurons inhibiting PRL secretion, as well as neurons facilitating GH secretion.

Inhibition of prolactin secretion by endothelm-3 is pertussis toxm-sensitive

The effect of pertussis toxin (PTX) pretreatment on endothelin-3 (ET-3)-mediated inhibition of prolactin secretion from primary cultures of rat anterior pituitary cells was examined. Monolayer cultures of anterior pituitary cells were treated with either 20 ng/ml PTX dissolved in media or with media alone (control) on the third day of culture. Exactly 24 h after PTX pretreatment, cells were challenged with either 100 nM ET-3 dissolved in media or media alone (control) for 4 or 48 h. ET-3 significantly (P less than 0.01) inhibited prolactin secretion in both the 4 and 48 h incubations. However, if the cells had been previously treated with PTX, ET-3 did not significantly affect prolactin secretion. These data suggest that a PTX-sensitive G protein mediates ET-3-induced inhibition of prolactin secretion and that ET-3 may invoke a signal transduction mechanism in the lactotroph which is distinct from those described in other cell types.

Effects of anxiolytic drugs on the catecholamine and DOPAC (3, 4-dihydroxyphenylacetic acid) levels in brain cortical areas and on corticosterone and prolactin secretion in rats subjected to stress ☆

Abstract The effects of anxiolytics like diazepam, tofisopam and chlorpropanol—a beta adrenergic inhibitor—were investigated in rats subjected to stressful stimuli. Catecholamines and DOPAC (3,4-dihydroxy-phenylacetic acid) levels in brain cortical areas and in the median eminence, as well as plasma prolactin and corticosterone concentrations, were measured. (1) Electric foot shock increased the DOPAC level in the frontopolar, entorhinal and cingular cortex. (2) This increase in the frontopolar cortex was inhibited by diazepam and chlorpropanol, but not by tofisopam. (3) No change in catecholamine or DOPAC level was obtained in the median eminence of stressed or drug-treated animals. (4) Both tofisopam and diazepam increased the noradrenaline level in the olfactory bulb of rats subjected to electric foot shock stress. (5) The increase of corticosterone and prolactin secretion induced by foot shock or by swimming-induced stress were not influenced by anxiolytics.

The Endogenous Stimulatory Rhythm Regulating Prolactin Secretion Is Present in the Lactating Rat

Prolactin (PRL) secretion in the female rat is regulated by an endogenous stimulatory rhythm (ESR), which is normally under the tonic inhibition of dopamine (DA). The ESR consists of a nocturnal (N) component which peaks at approximately 03.00 h, and a diurnal (D) component which peaks at approximately 17.00 h. This ESR has been shown to be present in ovariectomized and cervically stimulated rats. We have proposed that the ESR is continuously present in the female rat and that any suppression of the tonic inhibitory influence on PRL secretion can reveal its existence. In this study, the effects of the DA-lowering stimulus of suckling was investigated at different times of day in lactating rats. In addition, the pattern of PRL secretion in freely lactating rats throughout a 24-hour period was studied. Female rats were separated from their pups for 6 h prior to reunion at either 03.00 (coincident with the N component), 12.00 (control) or 17.00 h (coincident with the D component) at various stages of lactation. Blood samples were collected from intra-atrial cannulae immediately before separation of pups and dams, immediately before reunion of pups and dams (0 time), and 15, 30, 60 and 120 min following reunion of pups and dams. Four days following parturition, dams suckled at either 03.00 or 17.00 h secreted significantly greater PRL than rats suckled at 12.00 h. Peak levels of PRL were 60-, 90- and 25-fold greater than 0 time levels, at 03.00, 17.00 and 12.00 h, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Loss of sensitivity to morphine induced by prolonged ACTH treatment

The effect of long term ACTH treatment on some actions of morphine were studied. The effect of ACTH administration was compared to that induced by acute dexamethasone injection. ACTH caused a delayed inhibition of the morphine induced increase in growth hormone secretion demonstrable 24 hr after the last hormone injection. The morphine induced increase of striatal DOPAC (3,4-dihydroxyphenylacetic acid) content was also inhibited by ACTH treatment, however, neither the analgesia, nor the hypermotility caused by morphine were affected. Dexamethasone did not alter significantly the responsiveness to morphine. It is concluded that the prolonged exposure to ACTH presumably causes a corticosterone-mediated loss of responsiveness of functionally restricted opiate sensitive mechanisms in the central nervous system.

Endothelin-like immunoreactivity in lactotrophs, gonadotrophs, and somatotrophs of rat anterior pituitary gland are affected differentially by ovarian steroid hormones.

It has been previously found that all hormone-producing phenotypes of the anterior lobe of the pituitary gland are capable of producing endothelin (ET)-like substances. The aim of this study was to determine whether the expression of ET-1-like peptides in lactotrophs, gonadotrophs, and somatotrophs is influenced by different in vivo ovarian hormonal conditions. Anterior lobes of the pituitary gland were harvested from ovariectomized and ovarian steroid-replaced adult female rats 10–12 d after surgery. Quantitative immunocytochemistry was performed on enzymatically dispersed pituitary cells. The presence of ET-1-like immunoreactivity in prolactin-, luteinizing hormone-, or growth hormone-producing cells was demonstrated by double-label immunocytochemistry. The incidence of ET-1 immunopositive pituitary cells was unaffected by progesterone treatment alone. Estradiol replacement caused a modest decrease in the number of lactotrophs and somatotrophs expressing ET-1 but increased the incidence of ET-1 immunopositive cells among gonadotrophs. Combined treatment with estradiol and progesterone robustly increased the incidence of ET-1 immunopositive lactotrophs and gonadotrophs but had no effect on somatotrophs. These data reveal that the synthesis of ET-1-like peptides in lactotrophs and gonadotrophs (and, to a lesser extent, in somatotrophs) is sensitive to ovarian steroids. Furthermore, these findings predict that ovarian steroids modulate ET-1 biosynthesis during the estrous cycle, suggesting a possible mechanism by which the ovarian steroid milieu may regulate the responsiveness of lactotrophs and gonadotrophs to their hypothalamic secretagogues.