The effect of ethanol on prolactin release from pituitary cells in vitro

Effect of ethanol on 24-h hormonal changes in prolactin release mechanisms in growing male rats

This study analyzes the effect of chronic ethanol feeding on 24-h variation of hypothalamic-pituitary mechanisms involved in prolactin regulation in growing male Wistar rats. Animals were maintained under a 12:12 h light/dark photoperiod (lights off at 2000 h), and they received a liquid diet for 4 wk, starting on d 35 of life. The ethanol-fed group received a similar diet to controls except that maltose was isocalorically replaced by ethanol. Ethanol replacement provided 36% of the total caloric content of the diet. Rats were killed at six time intervals every 4 h, beginning at 0900 h. Mean concentration of serum prolactin in ethanol-fed rats was 58.7% higher than in controls. Peak circulating prolactin levels occurred at the early phase of the activity span in both groups of rats, whereas a second peak was found late in the resting phase in ethanol-fed rats only. In control rats, median eminence dopamine (DA), serotonin (5-HT), gamma-aminobutyric acid (GABA), and taurine levels exhibited two maxima, the major one preceding prolactin release and a second one during the first part of the resting phase. Median eminence DA and 5-HT turnover (as measured by 3,4-dihydroxyphenylacetic acid, DOPAC/DA, and 5-hydroxyindoleacetic acid, 5-HIAA/5-HT ratio) showed a single maximum preceding prolactin, at 0100 h. Ethanol treatment did not affect median eminence DA or 5-HT levels but it decreased significantly their turnover rate. The midday peak in DA and 5-HT levels (at 1300 h) was abolished and the night peak (at 0100 h) became spread and blunted in the ethanol-fed rats. This was accompanied with the disappearance of the 0100 h peak in DA and 5-HT turnover and the occurrence of a peak in 5-HT turnover at 1700 h. Ethanol intake suppressed the night peak in median eminence GABA and taurine (at 0100 h) as well as the midday peak of GABA. Ethanol augmented pituitary levels of DOPAC and 5-HIAA. The results indicate that chronic ethanol administration affects the mechanisms that modulate the circadian variation of prolactin release in growing male rats.

Effect of ethanol on 24-hour hormonal changes in peripubertal male rats

We analyzed the effect of chronic (4 weeks) ethanol feeding on 24-h variation of pituitary-testicular function in peripubertal male Wistar rats by measuring circulating concentrations of prolactin, follicle-stimulating hormone, luteinizing hormone, testosterone, and thyrotropin. Animals were maintained under a 12-h light: 12-h dark photoperiod and received a liquid diet for 4 weeks, starting on day 35 of life. The ethanol-fed group received a diet similar to that provided to control animals, except that maltose was replaced isocalorically with ethanol. Ethanol replacement provided 36% of the total caloric content of the diet. Rats were killed at one of six times around the clock, beginning at zeitgeber time (ZT) 1 (ZT 0 = lights on). In ethanol-fed rats globally, secretion of prolactin was augmented, whereas secretion of follicle-stimulating hormone, luteinizing hormone, testosterone, and thyrotropin was decreased. Significant changes in the 24-h secretory pattern of circulating hormones occurred in rats receiving ethanol, including the appearance of two peaks (at ZT 1 and ZT 9), rather than one peak, of follicle-stimulating hormone during the inactive phase of the daily cycle, suppression of the maximum plasma luteinizing hormone concentration during the first part of the inactive phase, and appearance of a second peak of testosterone and prolactin during the second part of the inactive phase (at ZT 5 and ZT 9, respectively) and of a second peak of plasma thyrotropin during the first part of the active phase (at ZT 13). The significant positive correlation between testosterone and individual luteinizing hormone and prolactin concentrations in control animals was no longer observed after ethanol administration. Chronic ethanol administration presumably affects the endogenous clock that modulates the circadian variation of the pituitary-gonadal axis and thyrotropin release in growing male rats.

Anesthetics inhibit high-affinity states of dopamine D2 and other G-linked receptors

The high-affinity states of dopamine D2 and D3 receptors, serotonin 5HT-2A receptors, beta-2-adrenoceptors, alpha-1 and alpha-2 adrenoceptors, opiate receptors, and muscarinic receptors were inhibited by clinical concentrations of anesthetics, including isoflurane, halothane, chloral hydrate, ketamine, and ethanol. The inhibition occurred not only in vitro, but also in vivo in rats anesthetized with isoflurane, with the high-affinity states recovering at different rates. Because the high-affinity states of G-protein-linked receptors are physiologically functional, their general inhibition by clinical concentrations of anesthetics may underlie general anesthesia and may explain some of the side effects of anesthetics. Subanesthetic concentrations of the anesthetics, including ketamine, stimulated the incorporation of GTP into the cloned dopamine D2 receptors. It is possible that the classical stage 2 excitement phase which occurs with subanesthetic concentrations of general anesthetics and ketamine may be associated with this general stimulation of a variety of G-protein-linked receptors, as found in the present study, while the stage 3 level of surgical anesthesia may be associated with the inhibition of the high-affinity states of several receptors.

Impact of acute and chronic ethanol exposure on prolactin in both male and female rats

The deleterious effects of ethanol (EtOH) on reproduction have been well documented. This disruption is usually associated with alterations in prolactin (PRL) levels, which is relevant since this hormone is an important participant in the reproductive system. Reported EtOH-induced changes in PRL (i.e., stimulation or inhibition) have varied. These differences may have been owing to the gender or age/sexual maturity of the animal and the mode of the administration of EtOH. Therefore, to clarify the impact of EtOH on PRL, a series of experiments were conducted utilizing rats of both genders, exposed to EtOH acutely or chronically, as adults and as they progressed through puberty. In general, in younger animals of both genders, EtOH depressed serum PRL whether given acutely or chronically. In adult males, acute EtOH actually stimulated PRL levels while chronic administration had no effect. In adult females, EtOH's effect was highly dependent on the stage of the estrous cycle in which EtOH was given and during which PRL was measured. In conclusion, our studies have shown that the PRL response to EtOH is dependent on the gender and age/sexual maturity of the animals as well as on the mode of administration.

Effects of thyrotropin-releasing hormone and metoclopramide on PRL secretion in normally cycling and amenorrheic alcoholic women

To assess the possible influence of alcoholism on the dopaminergic inhibitory control of prolactin (PRL) secretion, 10 mg of the dopaminergic antagonist metoclopramide (MTC), was injected i.v. in a group of eight healthy abstemious women (aged 28 +/- 6 (mean +/- S.E.) years) and in 16 aged-matched nondepressed female alcoholic subjects after 3-4 weeks of abstinence from alcohol. All normal controls and eight alcoholics had normal menstrual cycles and were tested in the early follicular phase (4-8 days), the remaining eight alcoholics were affected by amenorrhea (duration: 15 +/- 3 months). During the same period, all patients were also tested with TRH (200 micrograms in an i.v. bolus) to determine whether the pituitary PRL cell secretory capacity was preserved in alcoholics. The amenorrheic alcoholic group showed strikingly lower circulating estrogen levels than normally cycling groups. Similar basal PRL levels and PRL responses to TRH were observed in normal controls and normally cycling alcoholics, whereas basal and TRH-stimulated PRL levels were significantly higher in amenorrheic alcoholics. In contrast, the PRL response to MTC was significantly higher in cycling alcoholic patients than in normal controls and amenorrheic alcoholic subjects. However, when the statistical analysis of MTC test took into account the difference in estrogen levels among groups, the statistical differences in the PRL responses to MTC observed between normally cycling and amenorrheic alcoholics disappeared. These data suggest the presence of an enhanced dopaminergic inhibitory control of PRL secretion in 2-3 week abstinent alcoholics with normal menstrual cycles and normal circulating estrogen levels. In contrast, amenorrhea in abstinent alcoholics appears to be associated with an enhancement of PRL cell secretory activity.

Ethanol-induced alterations in the posttranslational processing, but not secretion of luteinizing hormone-releasing hormone in vitro

The effects of ethanol (EtOH) on the male hypothalamic pituitary reproductive axis are multiple and varied. Although direct gonadal toxicity has been reported, hypothalamic-pituitary perturbations have also been noted. The difficulty of sampling the hypothalamus has made direct investigation of EtOH-induced alterations on luteinizing hormone-releasing hormone (LHRH) fraught with interpretation problems. To circumvent this, we have conducted a series of experiments exploring the effect of 200 mg% EtOH in vitro on GT1-7 cells, a newly developed LHRH secreting neural cell line. Cell lines were treated with EtOH-containing or EtOH-free media for 2, 6, 24, or 48 hr. EtOH caused no significant change in LHRH secretion at any time point, although there was a trend to increased secretion after 2 hr EtOH exposure when compared with control. Significantly increased total (i.e., cellular plus secreted) pro-LHRH coupled with significantly reduced cellular LHRH after 6 hr only of EtOH exposure suggested that EtOH caused a transient decrease in processing from bioinactive pro-LHRH to bioactive LHRH. However, even at this time point, LHRH secretion from these EtOH-exposed cells was no different than from control cells. Steady-state LHRH mRNA levels were not changed by EtOH at any time point. These findings are concordant with previous in vitro data using hypothalamic tissue that has similarly demonstrated no effect of EtOH on LHRH secretion. Taken together with the in vivo demonstration that EtOH reduces hypothalamic-pituitary portal blood levels of LHRH, these data indicate that EtOH exerts its effect either at an extrahypothalamic locus and/or on non-LHRH-producing cells within the hypothalamus.

Acute ethanol administration in diestrus-2 in the rat on pulsatile prolactin and LH release

Exposure to ethanol is followed by changes in reproductive function in man and animals, characterized by modifications in the secretion patterns of prolactin and luteinizing hormone (LH). As both hormones are secreted in an episodic fashion, the present work was undertaken to study the effects of acute ethanol administration on pulsatile prolactin and LH secretion patterns in adult female rats. Rats were previously cannulated to allow a continuous blood withdrawal to study the pulsatile patterns of prolactin and LH. The mean values of prolactin during the bleeding period and the absolute pulse amplitude of prolactin peaks were significantly increased by acute ethanol administration, whereas a significant decrease of relative pulse amplitude and frequency of this hormone was observed. On the other hand, ethanol administration increased the mean serum LH levels and the absolute and relative amplitudes of LH peaks. Ethanol treatment did not modify either frequency or duration of LH peaks. These data suggest that acute ethanol administration in adult female rats is followed by changes in the pulsatile prolactin and LH secretory patterns, which might be part of the mechanism to explain ethanol effects on the endocrine system.

Endogenous opioid mediation of the inhibitory effect of ethanol on the prolactin response to breast stimulation in normal women

The effect of ethanol on the prolactin (PRL) response to breast stimulation was tested in normal women. The possible role of endogenous opioids in the control of the PRL response to breast stimulation and ethanol action was also examined. Eleven normal women were tested four times on the 22nd day of four consecutive regular menstrual cycles. All women underwent mechanical breast stimulation (for 10 min) with the concomitant administration of normal saline, naloxone (2 mg in an iv bolus plus 10 mg over 75 min. or 4 mg in an iv bolus plus 20 mg over 75 min.), ethanol (50 ml in 110 ml of whiskey p.o.) or the combination of ethanol and naloxone. Serum PRL levels rose significantly after breast stimulation, with a mean peak response (71.4% higher than baseline at 20 min). The PRL response to breast stimulation was not changed by the treatment with the lower (2 plus 10 mg) or the higher (4 plus 20 mg) dose of naloxone, whereas it was strikingly decreased by ethanol (mean peak was 25% higher than baseline). However, when ethanol was given together with naloxone, the peak rise induced by breast stimulation was only partially inhibited by ethanol (the mean PRL peak was 46.2% higher than baseline). At both doses naloxone produced similar effects. These data demonstrate that ethanol inhibits the PRL response to breast stimulation. Naloxone-sensitive endogenous opioids do not appear to be involved in the control of the PRL rise induced by breast stimulation. In contrast, since naloxone partially reversed the inhibiting effects of ethanol, a partial involvement of opioid peptides in ethanol action is supposed.

Alcohol effects on TRH-induced prolactin response in lactating rats: in vivo and in vitro studies

The site of action of alcohol in inhibiting suckling-induced prolactin release in lactating rats was examined by in vivo and in vitro studies. In vivo, sulpiride- and thyrotropin-releasing hormone (TRH)-induced prolactin release was studied in lactating rats separated from their litter. On day 7, dams were implanted with an atrial catheter. On day 10, pups were removed from dams at 0800 h and, after 5 h, an extension was attached to the catheter. An hour later, a baseline blood sample was removed and was followed by sulpiride (40 micrograms/kg) administration. Additional blood samples were withdrawn over 1 h. After the 60-min sample, sulpiride-administered rats were infused with 0.0, 1.0, or 2.0 g/kg b.wt. alcohol. Following alcohol, a postinfusion blood sample was removed, TRH (4.0 micrograms/kg) was administered, and subsequent blood samples were obtained 5, 10, 20, and 30 min after TRH. For in vitro studies, cells from lactating rats in midlactation were enzymatically dissociated, plated, and on culture day 5 were exposed to 0 or 10 nM TRH. Each set of cells were additionally exposed to 0, 100, or 300 mg% alcohol and media harvested after 4 h. In a subsequent study, plated cells were exposed to increasing doses of TRH in the presence of 0, 100, or 300 mg% alcohol and media harvested as above. Prolactin in plasma (in vivo studies) and medium (in vitro studies) was measured by RIA.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo studies of ethanol on prolactin and luteinizing hormone in rats and mice

The interaction of ethanol (EtOH), prolactin (Prl) and luteinizing hormone (LH) was examined in two studies. In the first study, adult male C57B1/6J mice were given a single intraperitoneal injection of either vehicle or Prl at 5, 10 and 20 mg/kg and a significant dose-related suppression of ethanol consumption was found. This injection did not cause any differences in food intake or body weight. Additionally, a 5 mg/kg dose of Prl was also given to adult male Long Evans Hooded rats and, similarly, there was a significant suppression of ethanol consumption. In a second study, when rats were given a free choice between water and 5% EtOH, three subgroups were found regarding the amount of EtOH consumption: low, medium and high. After 2 weeks of free choice, hypothalamic, but not serum Prl and LH levels, were significantly increased in EtOH-imbibing groups compared to controls. These findings suggest important interactions between EtOH consumption and ambient levels of Prl and LH.

Serum prolactin increase induced by ethanol--a dose-dependent effect not related to stress

The effect of moderate ethanol doses (0.5 and 1 g/kg body weight) on serum prolactin (PRL), cortisol, epinephrine and norepinephrine concentrations was measured in a double-blind, placebo-controlled study. Eight healthy male volunteers participated. Blood was with drawn twice before, and 30 min, 60 min, 90 min and 120 min after oral ethanol intake. The higher ethanol dose, but not the lower dose, significantly increased PRL concentrations. Concentrations of cortisol, epinephrine and norepinephrine were not changed by either dose. Thus, the effect of ethanol on PRL appears to be dose-dependent and not stress-related.

The effect of in vitro ethanol exposure on LHRH release from perifused rat hypothalami

A variety of indirect data suggest that the luteinizing hormone (LH) lowering effects of ethanol (ETOH) are mediated at a hypothalamic level decreasing the synthesis and/or release of LH-releasing hormone (LHRH). Little direct data support this concept, however. The current study was, therefore, designed utilizing a perifusion system with frequent sampling for LHRH with and without ethanol added to determine if ethanol had a direct effect on basal or stimulated LHRH release. A variety of secretagogues, including dopamine, norepinephrine, naloxone, prostaglandin E2, and a high dose of potassium were utilized. Ethanol at a dose of 300 mg% did not alter either basal or secretagogue-stimulated LHRH release from the hypothalami of ethanol-naive male rats. Thus, ethanol did not appear to have a direct effect on LHRH in this system. Alterations in LHRH release by ethanol may occur at a suprahypothalamic level, involving neurotransmitter-LHRH interactions. Alternatively, the well-described lowering effect of ethanol on LH may be secondary to a direct pituitary locus of action, or involve a metabolic breakdown product of ethanol rather than ethanol itself.

The effect of in vitro ethanol exposure on basal growth hormone secretion

Suppressive effects of ethanol (ETOH) on in vivo serum growth hormone (GH) levels have been reported in both humans and animals. To determine whether this effect could be mediated directly at the pituitary level, we have designed a series of in vitro experiments utilizing pituitary cells from ETOH naive animals maintained in monolayer culture. We report that ETOH, in doses ranging from 50 to 400 mg%, caused a prompt and sustained reduction in basal GH secretion, as well as a significant fall in intracellular GH content. These data establish that the in vivo effects of ETOH on GH can be accounted for, at least in part, by a direct effect at the pituitary level, possibly due to reduced GH synthesis.