Studies of Acute Alcohol Effects in Women and Animal Models

2015

Alcohol Effects on Basal Hormone Levels

Another approach to examination of alcohol’s toxic effects on reproductive function is to administer a single acute dose of alcohol to a normal healthy woman or experimental animal and measure the effects on pituitary and ovarian steroid hormones. Through a systematic manipulation of alcohol dose and changes in hormone levels, it should be possible to establish whether alcohol primarily disrupts hypothalamic, pituitary, or ovarian function. Surprisingly, studies of acute alcohol administration have shown that alcohol has minimal effects on basal hormone levels. Alcohol did not significantly suppress LH or estradiol in normal women or in female macaque monkeys. These data suggest that a single episode of intoxication is probably not sufficient to suppress normal basal hormone levels and that repeated episodes of intoxication are required to produce the hormonal correlates of amenorrhea, anovulation, and luteal phase dysfunction observed in clinical studies. One procedural difficulty affecting all investigations of acute alcohol effects on basal hormone levels is that studies have usually been conducted during the early follicular or luteal phase of the menstrual cycle, when basal hormone levels are relatively low and it is more difficult to detect an alcohol-related hormone suppression. Accurate prediction of the periovulatory period when estradiol, LH, and FSH levels are high is also difficult in women and primate models. Consequently, some investigators have adopted an alternative strategy of artificially stimulating hormone levels and then examining alcohol’s effects.

Alcohol Effects on Artificially Stimulated Pituitary and Gonadal Hormones

In clinical endocrinology, a series of provocative tests are used to stimulate pituitary and gonadal hormone secretion and to evaluate pituitary, hypothalamic, and ovarian function. The recent availability of these provocative tests provides a tool for analysis of alcohol’s effects on each component of the hypothalamic-pituitary-gonadal axis. The opioid antagonists naloxone and naltrexone can be used to stimulate hypothalamic release of endogenous LHRH, which stimulates pituitary release of gonadotropins LH and FSH (). Synthetic LHRH can be used to directly stimulate pituitary release of LH and FSH (). Techniques used to examine ovarian function either mimic or stimulate the actions of endogenous gonadotropins. Chorionic gonadotropins (naturally secreted by the placenta during early pregnancy) are used to stimulate ovulation in women with pituitary insufficiency infertility. Antiestrogen compounds, like clomiphene and tamoxifen, appear to act by competing for estrogen-binding sites in the hypothalamus and pituitary and diminishing the number of estrogen receptors available for endogenous estrogen. Antiestro-gens prevent normal hypothalamic and pituitary feedback inhibition of the control of estrogen synthesis, which culminates in an increased pituitary gonadotropin secretion and ovarian stimulation (). Data obtained using each of these provocative tests are described separately.

Alcohol Effects on LHRH-Stimulated Gonadotropins. Anterior pituitary function can be analyzed by administration of synthetic LHRH. Synthetic LHRH acts like endogenous hypothalamic LHRH to stimulate release of anterior pituitary gonadotropins LH and FSH. A normal pituitary response to LHRH stimulation in women is an LH increase of about 10-20 ml.U./ml, usually within about 30 min, and an increase in FSH within about 45 min.

Alcohol (2.5 and 3.5 k/kg) prevented synthetic LHRH stimulation of FSH in normal female rhesus monkeys studied during the follicular phase of the menstrual cycle. However, LHRH-stimulated LH increased significantly (p < 0.001) within 15 min when blood alcohol levels averaged 184 (± 14.3) and 276 (± 14.9) mg/dl. Under sucrose control conditions, LHRH stimulated significant increases in both LH and FSH within 30 and 80 min, respectively. Since FSH is essential for normal follicle development and maturation during the follicular phase, an alcohol-related inhibition of FSH responsivity to LHRH stimulation could result in menstrual cycle irregularities commonly seen in alcohol-dependent females. As noted earlier, suppression of FSH could delay follicle maturation and ovulation or result in luteal phase dysfunction after timely ovulation.

The selective alcohol blockade of LHRH-stimulated FSH is also consistent with the hypothesis that FSH release and LH release are controlled by different factors. McCann and co-workers postulate that a separate hypothalamic-releasing factor, follicle-stimulating hormone-releasing factor (FSHRF), controls FSH activity. There is also considerable evidence that a nonsteroidal ovarian peptide, inhibin, suppresses FSH without affecting LH (). As discussed earlier in connection with clinical studies of luteal phase dysfunction, FSH appears to be regulated by an interaction between endogenous LHRH/FSHRF stimulation and suppression by a gonadal peptide, inhibin (). Whether or not alcohol also selectively blocks LHRH-stimulated FSH in women remains to be determined.

Since the release of pituitary gonadotropins in normal females is necessarily influenced by the ovarian steroid/peptide milieu, alcohol effects on LHRH-stimulated LH and FSH were reexamined in ovariectomized female rhesus monkeys under the same conditions. In ovariectomized females after sucrose control administration, LHRH stimulated a significant increase in LH within 30 min (p < 0.001) and in FSH within 60 min (p < 0.01). After alcohol administration, LHRH-stimulated LH and FSH also increased significantly (p < 0.01) when blood alcohol levels averaged 242 (± 26) and 296 (± 29) mg/dl. Figure “LHRH-stimulated LH after alcohol and sucrose in ovariectomized female rhesus monkeys. LH levels are shown as the percent change from the pre-alcohol or presucrose baseline. Twenty-minute integrated plasma samples, numbers 1-6, were collected immediately following administration of sucrose control solutions (open circles), 2.5 g/kg alcohol (closed squares), or 3.5 g/ kg alcohol (closed diamonds). Samples 7-16 follow administration of synthetic LHRH (100 (xg). Each data point represents samples from five ovariectomized monkeys” shows an alcohol-dose-dependent increase in LHRH-stimulated LH (p < 0.01, 0.001) in comparison to control conditions, even though prealcohol and presucrose LH levels were equivalent. LHRH-stimulated FSH was also higher after 3.5 g/kg alcohol than after 2.5 g/kg alcohol and sucrose control administration (p < 0.001), but baseline FSH levels prior to 3.5 g/kg alcohol were also higher than control or 2.5 g/kg alcohol.

It is difficult to account for the significant alcohol-related increase in LHRH-stimulated LH shown in Figure “LHRH-stimulated LH after alcohol and sucrose in ovariectomized female rhesus monkeys. LH levels are shown as the percent change from the pre-alcohol or presucrose baseline. Twenty-minute integrated plasma samples, numbers 1-6, were collected immediately following administration of sucrose control solutions (open circles), 2.5 g/kg alcohol (closed squares), or 3.5 g/ kg alcohol (closed diamonds). Samples 7-16 follow administration of synthetic LHRH (100 (xg). Each data point represents samples from five ovariectomized monkeys”. LHRH-stimulated LH was also significantly greater after 3.5 g/kg alcohol than sucrose control in intact normal female monkeys, but there was no alcohol-dose-dependent enhancement of LH. Increased pituitary sensitivity to synthetic LHRH stimulation after alcohol administration could reflect alcohol’s effects on endogenous LHRH or on other hormones known to modulate pituitary sensitivity to LHRH, such as estradiol. Although ovariectomy reduces circulating estradiol by approximately 60%, estrogens are produced in the adrenals and through peripheral conversion of androgens to estrogens. Increased estradiol could enhance the LH response to LHRH stimulation, just as the midcycle LH surge in normally cycling rhesus females is dependent on the periovulatory increase in estradiol. There is also evidence that estradiol pretreatment increases pituitary sensitivity to LHRH stimulation in normal and hypogonadal women and in the intact diestrus rat. Consequently, if alcohol administration did increase estradiol levels, this could have sensitized the pituitary to produce an augmented LH response to LHRH stimulation. Unfortunately, estradiol was not measured in these ovariectomized females, so direct evidence to confirm or refute the hypothesis that alterations in steroid biotransformation associated with intrahepatic ethanol catabolism may have increased plasma estradiol is unavailable. However, as discussed in Section Opioid Antagonist Stimulation of Hypothalamic Function, alcohol-related increases in estradiol have also been seen following opioid antagonist stimulation in normal women. Significant increases in estradiol were also reported in oophorectomized rats exposed to a moderate dose of alcohol for 10 weeks.

The finding that alcohol did not delay or attenuate an LHRH-stimulated increase in LH in comparison to sucrose control conditions in normal and ovariectomized rhesus monkey is concordant with earlier findings in ovariectomized rats given LHRH 140 min after administration of 3.0 g/kg alcohol i.g. There was also no difference in LHRH-stimulated LH in post-menopausal alcoholic women during sobriety as compared to control women. The contrast between alcohol’s effects on LHRH-stimulated FSH in ovariectomized and normally cycling rhesus monkeys suggests the importance of ovarian negative feedback on pituitary FSH secretory cell activity in modulating alcohol effects. The ovarian peptide inhibin has been shown to suppress FSH without affecting LH in several species under many conditions (). Further studies will be required to clarify the contribution of ovarian peptides and/or steroids to alcohol’s effects on LHRH-stimulated FSH. However, these data do suggest that in the absence of ovarian modulation, alcohol and synthetic LHRH may act synergistically to stimulate pituitary gonadotropin secretion.

Opioid Antagonist Stimulation of Hypothalamic Function. The demonstration of endogenous opiate receptors in brain in the early 1970s was rapidly followed by identification of endogenous opioids called enkephalins. Subsequently other opioid peptides (β-endorphin, dynorphin) were identified. These endogenous opioid peptides, especially p-endorphin, are highly concentrated in the hypothalamus. It has long been known that opiates, such as morphine or heroin, suppress gonadotropin release, and it now appears that the inhibitory regulation of endogenous LHRH is mediated by endogenous opioids. Administration of opioid antagonist drugs rapidly stimulates the release of pituitary gonadotropins, presumably by antagonism of endogenous opioid peptides. Two opioid antagonists, naloxone and naltrexone, are now used to stimulate hypothalamic release of endogenous LHRH followed by pituitary release of LH, FSH, and prolactin. The long-acting antagonist naltrexone also stimulates release of ACTH and cortisol in women.

Naloxone is a short-acting narcotic antagonist that is most effective in stimulating LH release during the late foUicular and midluteal phases of the menstrual cycle (). Naloxone is only available for intravenous infusion. The half-life of naloxone in plasma is about 1 hr, and its duration of opioid antagonist action is 1-4 hr after parenteral administration. Naltrexone, a long-acting narcotic antagonist, also stimulates gonadotropins, prolactin, ACTH, and cortisol during the early follicular phase of the menstrual cycle in normally cycling women. Naltrexone is available in oral tablets and is rapidly absorbed. Naltrexone reaches peak plasma levels within 60 min and its half-life in plasma is 10 hr. Naltrexone’s opioid antagonist actions may persist for as long as 24 hr.

The effects of alcohol (1 ml/kg of 95% ETOH) or placebo on opioid antagonist stimulation of pituitary and gonadal hormones have been examined in normal women. Naloxone (5 mg i.v.) stimulation was studied in nine women during the midluteal phase of the menstrual cycle, and naltrexone (50 mg p.o.) was studied in 10 women during the midluteal phase of the menstrual cycle. Each subject served as her own control in a double-blind study. Progesterone levels were equivalent (13.9 ng/ml) during alcohol and placebo control conditions. Intravenous naloxone was administered at the rate of 1 ml/min concurrently with initiation of consumption of alcohol placebo or alcohol. Peak blood alcohol levels averaged 100 mg/dl within 45-60 min after drinking. Under placebo control conditions, naloxone stimulated a significant increase in plasma LH and prolactin, but did not increase estradiol or progesterone. Alcohol did not attenuate the significant naloxone stimulation of LH (p < 0.001), and progesterone levels were equivalent under alcohol and control conditions, but alcohol significantly enhanced naloxone stimulation of prolactin and estradiol. The increase in naloxone-stimulated estradiol after alcohol administration was sustained throughout the 180-min sampling period.

A similar pattern of alcohol effects on pituitary, gonadal, and adrenal hormones was observed after naltrexone stimulation. Normal women were studied on two occasions under double-blind conditions during the midluteal phase of the menstrual cycle, and average progesterone levels ranged between 11 and 14 ng/ml. To ensure complete absorption of oral naltrexone (50 mg), alcohol (1 ml/kg of 95% ETOH) or placebo control solutions were administered 1 hr after naltrexone. Peak blood alcohol levels averaged 94 mg/dl. Naltrexone significantly increased plasma LH, prolactin, and cortisol levels but did not affect estradiol or progesterone under placebo control conditions. After alcohol administration, naltrexone also stimulated a significant increase in LH levels and significantly increased estradiol, prolactin, and cortisol in comparison to placebo control conditions. Estradiol data for a representative women are shown in Fig. “Plasma estradiols for a representative woman studied during the midluteal phase. Closed squares show estradiol levels following naltrexone (50 mg p.o.) and placebo administration. Open squares show estradiol levels following naltrexone (50 mg p.o.) and alcohol (1 ml/kg 95% ETOH)”.

Although alcohol did not enhance opioid-antagonist-stimulated LH in midluteal phase women as was observed following LHRH stimulation in ovariectomized rhesus monkeys, these data confirmed previous findings from studies of alcohol effects on basal LH levels that this anterior pituitary hormone is relatively resilient to the effects of a single dose of alcohol. The rapid increase in plasma estradiol following alcohol plus naloxone or naltrexone was surprising. It was postulated that alcohol might increase estradiol production and/or decrease estradiol metabolism. Since intrahepatic ethanol metabolism decreases NAD availability for other coupled oxidative reactions, this in turn might reduce the rate of oxidation of estriol to estrone and result in elevated estradiol levels. An alcohol-related enhancement of opioid-antagonist-stimulated prolactin could be related to the increase in estradiol. Estrogens have been reported to increase prolactin secretion in experimental animals and human subjects, and a modulating effect of estradiol on prolactin secretion is believed to occur at both the hypothalamic and pituitary levels.

The alcohol-induced enhancement of naltrexone-stimulated cortisol is also probably due to a synergistic effect of alcohol plus naltrexone on pituitary release of ACTH. Naltrexone administration alone stimulates increased plasma ACTH levels which are followed by subsequent plasma cortisol increases in normal women.

Alcohol Effects on Ovarian Stimulation. We are unaware of any recent studies of acute alcohol effects on ovarian function as assessed with human chorionic gonadotropin (hCG) or clomiphene in normal women. As noted earlier, administration of hCG or clomiphene to alcoholic women during sobriety showed that most amenorrheic patients had an adequate increase in estradiol. However, three of four women with low basal estrogen levels did not show an estradiol response to hCG. The response to clomiphene or hCG stimulation was adequate in women categorized as anovulatory or with luteal phase inadequacy. Hugues and co-workers concluded that primary ovarian dysfunction seemed improbable despite some negative hCG tests in this sample.

 

Selections from the book: “Recent Developments in Alcoholism. Volume 6: Posttraumatic Stress Disorder. The Workplace. Consequences in Women. Markers for Risk.” Edited by Marc Galanter. An Official Publication of the American Medical Society on Alcoholism, the Research Society on Alcoholism, and the National Council on Alcoholism. 1986.