The effect of in vitro ethanol exposure on luteinizing hormone and follicle stimulating hormone mRNA levels, content, and secretion

The chronic alcohol consumption influences the gonadal axis in men: Results from a meta-analysis

BACKGROUND

Low testosterone concentrations affect 2-13% of adult males, with a direct association between reduction in testosterone (T) concentrations and cardiovascular events. Lifestyle habits have been linked to visceral fat accumulation and endocrine disorders like secondary hypogonadism. Alcohol intake has also been a topic of debate, with studies showing a detrimental effect on sperm production and underlying mechanisms. This meta-analysis aims to comprehensively evaluate the effect of alcohol consumption on T serum concentrations in adult men.

METHODS

The literature search included only controlled clinical trials comparing men who drink alcohol to men who do not, or who assumed placebo or nonalcoholic beverages. The primary outcome was the comparison of total testosterone serum concentrations between the study and control groups. The publications were examined for publication bias using Egger's test.

RESULTS

Twenty-one studies were included in the analysis for a total of 30 trials that examined the effects of alcohol consumption on testosterone level in 10,199 subjects. The meta-analysis showed that alcohol consumption overall is related to significant reduction in circulating concentrations of total testosterone (mean difference [MD] = -4.02; 95% CI -6.30, -1.73), free T (MD = -0.17; 95% CI -0.23, -0.12), sex hormone binding globulin (SHBG) (MD = -1.94; 95% CI -3.37, -0.48), an increase in estradiol (E2) (MD = 7.65; 95% CI 1.06, 14.23) and neutral effect on luteinizing hormone (LH) (MD = -0.15; 95% CI -0.36, 0.06), independently by age, body mass index (BMI), E2, and LH serum concentrations and alcohol intake. However, these results are evident only in healthy men exposed to chronic alcohol consumption and not in those with a recognized diagnosis of alcohol use disorder or after acute alcohol intake.

CONCLUSION

This study suggests how chronic alcohol consumption may inhibit the gonadal axis in healthy men, although the exact pathophysiological mechanisms connecting alcohol exposure and steroidogenesis are still not completely clarified.

Effects of red ginseng extract on the epididymal sperm motility of mice exposed to ethanol

The protective effects of red ginseng extract and ginseng wine against ethanol-induced male reproductive toxicity were evaluated in male mice using computer-assisted sperm analysis. Mice were divided into 4 groups of 10 and fed plain saline, 6 g/kg per d of ethanol in saline, red ginseng extract plus ethanol, or a fermented preparation of red ginseng extract daily for 5 weeks. We found that the average seminal vesicle weight was significantly lower in the ethanol-treated group compared to the control group, while those of the ginseng-treated groups tended to be higher than the ethanol-treated group. We found a significant decrease in sperm motility and progressiveness in mice treated with ethanol for 5 weeks, while administration of ethanol plus red ginseng extract appeared to minimize the negative effects of ethanol toxicity on male fertility. Serum testosterone, luteinizing hormone (LH), and follicle stimulating hormone (FSH) were insignificantly lower in the ethanol-treated group than in the control group.

Suppression by ethanol of male reproductive activity

Ethanol has been known to suppress reproductive activity in laboratory animals and humans through the inhibition of luteinizing hormone (LH) release by reduction of gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus. There are, however, little data is available regarding the effect of ethanol on GnRH gene expression. Thus, the present study was designed to evaluate the effect of ethanol on GnRH gene expression and reproductive activity at all levels of the hypothalamus-pituitary-gonad (HPG) axis simultaneously. To this end, ethanol (3 g/kg i.p., 15% v/v in saline) was administered to adult male rats for 10 days. Serum levels of LH and testosterone were significantly decreased by ethanol. Using Northern blot analysis and in situ hybridization, the present study showed the reduction in GnRH mRNA levels in the hypothalamus by prolonged ethanol administration. The content of LH in the anterior pituitary was also significantly reduced by ethanol. In addition, steroidogenic acute regulatory protein (StAR) mRNA levels were significantly decreased by ethanol, suggesting a cause for the reduced production of testosterone under this condition. These results indicate that ethanol affects the HPG axis at all the levels. Especially, suppressed GnRH mRNA levels in the hypothalamus of ethanol-treated rats strongly demonstrated that hypothalamus is the major action site of ethanol on the HPG axis. Decreased serum LH level may affect the steroidogenesis in the testis, at least in part, through the inhibition of StAR gene expression that induces part of dysfunctions of reproductive activity.

Effect of alcohol on the proestrous surge of luteinizing hormone (LH) and the activation of LH-releasing hormone (LHRH) neurons in the female rat

Reproduction is adversely affected by alcohol abuse in humans and laboratory animals. In rats, alcohol exposure suppresses both luteinizing hormone (LH) and sex steroid secretion, although consensus is lacking as to which level of the hypothalamic-pituitary-gonadal (HPG) axis is primarily affected. We tested the hypothesis that acute alcohol treatment inhibits the HPG axis by blunting release of LH-releasing hormone (LHRH) in female rats, by examining the effect of this drug on the central reproductive endocrine event; i.e., the proestrous surge of gonadotropins, which triggers ovulation. In a first series of experiments, we injected alcohol at 8 A.M. and 12 P.M. on proestrus and measured plasma levels of LH, estradiol (E2), and progesterone during the afternoons of proestrus and estrus. Alcohol administration blocked the proestrous surge of LH and ovulation. In subsequent experiments, alcohol inhibited the surge of LHRH (measured by push-pull cannulation) and LHRH neuronal activation (measured by Fos labeling in LHRH neurons). Because alcohol also decreased E2 levels, we reasoned that it might have prevented positive feedback; however, alcohol retained its ability to inhibit the LH surge evoked by E2 implantation in ovariectomized females, disproving this hypothesis. Additionally, alcohol does not act via increased corticosteroid secretion, because alcohol also blocked the proestrous surge in adrenalectomized females. Last, exogenous administration of LHRH to alcohol-blocked animals evoked LH secretion and ovulation, indicating that pituitary and/or ovarian function could be restored by mimicking the hypothalamic signal. Collectively, these data indicate that in female rats, alcohol inhibits the gonadotropin surge primarily by decreasing LHRH secretion.

Alcohol rapidly lowers plasma testosterone levels in the rat: evidence that a neural brain-gonadal pathway may be important for decreased testicular responsiveness to gonadotropin

Alcohol is reported to suppress testosterone (T) secretion in the adult male rat. Decreases in the circulating levels of luteinizing hormone (LH) and/or the activity of testicular steroidogenic enzymes have been proposed as putative mechanisms underlying this inhibitory effect. We have recently provided functional evidence for a neural pathway between the brain and the male gonads that plays an important role in the ability of brain proinflammatory cytokines to blunt testicular responsiveness to human chorionic gonadotropin (hCG). The present work was designed to test the hypothesis that a similar pathway might be implicated in the inhibitory influence of alcohol on T secretion. Alcohol, administered intraperitoneally or intragastrically, significantly prevented the T response to the gonadotropin. This effect was significant within 15 min of drug treatment. In the intragastric model (the only one used for this type of experiment), the effect of alcohol was not altered by prior blockade of LH release, which suggests that it is independent of changes in the activity of the pituitary gonadotrophs. The lowest effective dose of alcohol, delivered intraperitoneally, was 2.0 g/kg. The intracerebroventricular injection of the alpha- and beta-adrenergic receptor antagonists phentolamine and propranolol significantly reversed the inhibitory influence of alcohol when it was administered 15 min, but not 60 min, before hCG. Collectively, our results indicate that (1) alcohol induces a rapid and profound decrease in plasma T levels that is secondary to decreased testicular responsiveness to hCG; and (2) at least part of this acute inhibitory action of alcohol may depend on the activation of a neural, adrenergic-dependent pathway between the brain and the testes.

The effect of acute ethanol (EtOH) exposure on protein kinase C (PKC) activity in anterior pituitary

Alterations in the protein kinase C (PKC) pathway may interrupt anterior pituitary luteinizing hormone (LH) synthesis and/or secretion, which may impair normal reproductive function. Work by our laboratory and others has shown that EtOH has profound deleterious effects on the regulation of the hypothalamic-pituitary-gonadal (HPG) axis. The present study focuses on PKC translocation from the cytosol to the membrane of anterior pituitary after acute EtOH exposure. Serum levels of LH were measured at three time points (15, 30, and 90 min) after an IP injection of either saline or 3 g/kg EtOH in adult castrated male rats. LH levels dropped significantly (p < 0.03) in EtOH-injected compared to saline-injected control animals. In the same animals, EtOH significantly suppressed PKC localization at its active site at the pituitary cell membrane (p < 0.05). These findings suggest that the mechanism of EtOH's suppression of LH is mediated, at least in part, through a decrease in PKC translocation to the anterior pituitary cell membrane.

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.

Failure of ethanol metabolites to alter gonadotropin secretion or luteinizing hormone synthesis in vitro

The impact of ethanol on the male reproductive axis are multiple and varied, with both gonadal and control hypothalamic-pituitary pertubations being reported. There appears to be a discrepancy, however, between the in vivo and in vitro effects of ethanol on hypothalamic luteinizing hormones releasing hormone (LHRH) and the pituitary gonadotropins luteinizing hormone (LH) and follicle stimulating hormone (FSH). While in vivo data suggests a decrease in LHRH release after EtOH, in vitro studies find no effect on secretion. Similarly, in vivo acute EtOH profoundly diminishes LH synthesis and secretion, while in vitro impaired release with no alteration in the transcription of beta LH has been found. A potential exploration for these discrept results could be the in vivo metabolism of EtOH into acetaldehyde and acetate, or the subsequent formation of salsolinol, a product of acetate combining with dopamine. To test this possibility, a series of in vitro experiments were conducted exposing dispensed anterior pituitary cells from male rats to different doses of acetaldehyde, acetate or salsolinol for varying amounts of time for which gonadotropin secretion and beta LH mRNA levels were assessed. The results demonstrated no effect of either acetaldehyde or acetate on basal or LHRH stimulated LH release, FSH release or steady-state beta LH mRNA levels. These data suggest that the metabolites of EtOH, which occur in vivo but not in vitro, are not responsible for the discrepant gonadotropin changes reported between the in vivo and in vitro setting. Other potential mechanisms to explain this phenomenon include differences in the molarity of EtOH, hyperprolactinemia and suprapituitary influences including hypothalamic LHRH, catecholamines, excitatory amino acids, substance P and beta endorphin.