Intragastric cannulation as a method of ethanol administration for neuroendocrine studies

Alcohol Delays the Onset of Puberty in the Female Rat by Altering Key Hypothalamic Events

BACKGROUND

Because alcohol (ALC) delays signs of pubertal development, we assessed the time course of events associated with the synthesis of critical hypothalamic peptides that regulate secretion of luteinizing hormone-releasing hormone (LHRH), the peptide that drives the pubertal process.

METHODS

Immature female rats were administered either laboratory chow or BioServe isocaloric control or ALC-liquid diets from 27 through 33 days of age. On days 28, 29, 31, and 33, animals were killed by decapitation and tissue blocks containing the medial basal hypothalamus (MBH) and the rostral hypothalamic area (RHA) were isolated and stored frozen until assessed by Western blot analysis.

RESULTS

Synthesis of dynorphin (DYN), a prepubertal inhibitor of LHRH secretion, was increased (p < 0.05) in the MBH of ALC-treated animals by day 29. DYN was further elevated (p < 0.01) on day 33 and was associated with an increase (p < 0.01) in DYN receptor expression. ALC did not affect synthesis of neurokinin B (NKB), a prepubertal stimulator of LHRH; however, it did suppress (p < 0.05) NKB receptor expression in the MBH by day 31. The most potent stimulator of prepubertal LHRH secretion, kisspeptin (Kp), was also decreased (p < 0.05) in the MBH as early as day 29, with continued suppression (p < 0.01) through day 33. Similar timely suppressions of mammalian target of rapamycin (mTOR), an immediate upstream regulator of Kp, were also noted. These decreases in mTOR and Kp were consistent with ALC stimulating (p < 0.05) the p-AMP-activated protein kinase/Raptor inhibitory pathway to mTOR on day 29, then later suppressing (p < 0.001) an Akt-mediated induction pathway to mTOR by day 31. In the RHA, ALC affected the pathways regulating Kp in a manner similar to that described in the MBH; however, these effects were not noted until day 33.

CONCLUSIONS

ALC acts within the MBH as early as 29 days to induce inhibitor and repressor inputs to LHRH, while depressing stimulatory inputs to the peptide. Collectively, these events lead to delayed signs of pubertal development.

Manganese protects against the effects of alcohol on hypothalamic puberty-related hormones

AIMS

Since manganese (Mn) is capable of stimulating the hypothalamic-pituitary unit and advancing female puberty, we assessed the possibility that this element might overcome some of the detrimental effects of prepubertal alcohol (ALC) exposure on the hypothalamic control of pituitary function.

MAIN METHODS

Rats received either saline or Mn (10mg/kg) daily by gastric gavage from day 12 to day 31. After weaning, all rats were provided Lab Chow diet ad libitum until day 27 when they began receiving either the Bio Serv control or ALC diet regime. On day 31, the medial basal hypothalamus (MBH) was collected to assess luteinizing hormone-releasing hormone (LHRH) and cyclooxygenase 2 (COX2) protein levels. Release of prostaglandin-E2 (PGE2), LHRH and serum luteinizing hormone (LH) were also assessed. Other animals were not terminated on day 31, but remained in study to assess timing of puberty.

KEY FINDINGS

Short-term ALC exposure caused elevated hypothalamic LHRH content, suggesting an inhibition in peptide release, resulting in a decrease in LH. Both actions of ALC were reversed by Mn supplementation. COX2 synthesis, as well as PGE2 and LHRH release were suppressed by ALC exposure, but Mn supplementation caused an increase in COX2 synthesis and subsequent PGE2 and LHRH release in the presence of ALC. Mn supplementation also ameliorated the action of ALC to delay puberty.

SIGNIFICANCE

These results suggest that low level Mn supplementation acts to protect the hypothalamus from some of the detrimental effects of ALC on puberty-related hormones.

Differential Effects of Alcohol on Excitatory and Inhibitory Puberty-Related Peptides in the Basal Hypothalamus of the Female Rat

BACKGROUND

An increase in development of excitatory inputs along with a decline in inhibitory inputs ultimately govern the timely increased secretion of hypothalamic luteinizing hormone-releasing hormone (LHRH) at the time of puberty. As chronic alcohol (ALC) exposure acts at the hypothalamic level to suppress LHRH secretion and delay puberty, we assessed its ability to differentially affect the expression of key puberty-related proteins.

METHODS

ALC was administered to female rats from days 27 to 33, at which time animals were killed and tissues collected for protein expression. In the medial basal hypothalamus (MBH), we assessed kisspeptin (Kp) 10, an excitatory peptide critical for prepubertal LHRH secretion, and Lin28b, a peptide with an inhibitory influence on puberty. As a direct mechanism of action of Lin28b was not known, we determined whether its central administration could induce dynorphin (DYN), a peptide that is inhibitory on LHRH secretion. Also, ALC's effect on DYN protein expression was assessed, as well as its effect on DYN release in vitro.

RESULTS

ALC markedly suppressed (p < 0.01) the expression of the excitatory Kp protein, while at the same time increased (p < 0.001) the expression of inhibitory Lin28b protein. Subsequently, we showed for the first time that the central administration of Lin28b stimulated (p < 0.01) the synthesis of DYN. Finally, ALC also induced (p < 0.01) the protein expression and stimulated (p < 0.01) the in vitro release of DYN from the MBH.

CONCLUSIONS

These results indicate that ALC can simultaneously and differentially alter both excitatory and inhibitory influences governing pubertal development, show for the first time a mechanism of action by which Lin28b exerts its prepubertal inhibitory tone, and further demonstrate the negative influences of ALC on the pubertal process.

Hypothalamic actions and interactions of alcohol and IGF-1 on the expression of glial receptor protein tyrosine phosphatase-β during female pubertal development

BACKGROUND

Hypothalamic glial-neuronal communications are important for the activation of luteinizing hormone releasing hormone (LHRH) secretion at the time of puberty. As we have shown that alcohol (ALC) diminishes prepubertal LHRH secretion and delays puberty, we first assessed the effects of short-term ALC administration on the basal expression of a specific gene family involved in glial-neuronal communications. Second, as insulin-like growth factor-1 (IGF-1) is a critical regulator of LHRH secretion and the pubertal process, we then assessed whether IGF-1 could induce the expression of these signaling genes and determine whether ALC can block this affect.

METHODS

Immature female rats were fed a liquid diet containing ALC for 6 days beginning when 27 days old. Control animals received either the companion isocaloric liquid diet or rat chow and water. Animals were decapitated on day 33, in the late juvenile stage of development. Medial basal hypothalamic (MBH) tissues were obtained for gene and protein analyses of glial receptor protein tyrosine phosphatase-β (RPTPβ) and the 2 neuronal components, contactin and contactin-associated protein 1 (Caspr1). In the second experiment, IGF-1 was administered into the third ventricle (3V) and the MBH removed 6 hours after peptide delivery, and the above-mentioned 3 genes were analyzed by real-time PCR. To determine whether this action was affected by ALC, immature female rats were administered either ALC (3 g/kg) or water via gastric gavage at 0900 hours. At 1030 hours, the ALC and control groups were subdivided such that half of the animals were injected into the 3V with IGF-1 and the other half with an equal volume of saline. Rats were killed 6 hours after the IGF-1 injection and MBHs collected.

RESULTS

Real-time PCR showed that when compared with control animals, ALC caused a marked decrease (p < 0.001) in the basal expression of the RPTPβ gene, but did not affect the expression of either contactin or Caspr1. Likewise, analysis by Western blotting demonstrated that ALC caused suppressed (p < 0.001) levels of the RPTPβ protein, with the expressions of both contactin and Caspr1 proteins being unaltered. In the second experiment, results showed that only the RPTPβ gene was stimulated (p < 0.05) by IGF-1 in the MBH 6 hours after peptide delivery. Assessments revealed that the IGF-1 induced increase (p < 0.01) in the expression of the RPTPβ gene was blocked by the presence of ALC.

CONCLUSIONS

Prepubertal ALC exposure is capable of interfering with hypothalamic glial-neuronal communications by suppressing the synthesis of the glial product, RPTPβ, which is required for binding to the contactin-Caspr1 complex on LHRH neuronal terminals, thus suggesting that this action of ALC contributes to its detrimental effects on the pubertal process.

Prepubertal ethanol exposure alters hypothalamic transforming growth factor-α and erbB1 receptor signaling in the female rat

Glial-derived transforming growth factor alpha (TGFα) activates the erbB1/erbB2 receptor complex on adjacent glial cells in the medial basal hypothalamus (MBH). This receptor activation stimulates the synthesis and release of prostaglandin-E(2) (PGE(2)) from the glial cells, which then induces the release of prepubertal luteinizing hormone-releasing hormone (LHRH) secretion from nearby nerve terminals; thus, showing the importance of glial-neuronal communications at the time of puberty. Ethanol (EtOH) is known to cause depressed prepubertal LHRH secretion and delayed pubertal development. In this study, we assessed whether short-term EtOH exposure could alter the hypothalamic glial to glial signaling components involved in prepubertal PGE(2) secretion. Immature female rats began receiving control or EtOH diets beginning when 27 days old. The animals were killed by decapitation after 4 and 6 days of treatment and confirmed to be in the late juvenile stage of development. Blood and brain tissues were collected for gene, protein, and hormonal assessments. Real-time polymerase chain reaction (PCR) analysis demonstrated that EtOH did not affect basal levels of erbB1 gene expression in the MBH. Expression of total erbB1 protein was also unaffected; however, the EtOH caused suppressed phosphorylation of erbB1 protein in the MBH at both 4 and 6 days (P<.01) as revealed by Western blotting. Phosphorylation and total protein levels of erbB2 receptor were not affected by EtOH exposure. Because this receptor is critical for PGE(2) synthesis/release, which mediates the secretion of LHRH, we assessed whether in vivo EtOH exposure could affect the release of PGE(2). EtOH exposure for 6 days suppressed (P<.01) basal levels of PGE(2) released into the medium. The effects of 4- and 6-day EtOH exposure on gene and protein expressions of TGFα, an upstream component in the activation of erbB1/erbB2, were also studied. The levels of TGFα mRNA were increased markedly at 4 days (P<.001), but declined to near basal levels by 6 days in the EtOH-treated animals. The EtOH caused increases in TGFα protein expression at both 4 (P<.001) and 6 (P<.01) days; hence, suggesting that the EtOH inhibited release of the peptide. We confirmed this inhibition by showing decreased (P<.01) TGFα released from MBHs incubated in vitro following 6 days of EtOH exposure in vivo. Thus, these results demonstrate that EtOH is capable of interfering with hypothalamic glial to glial signaling processes involved in prepubertal PGE(2) secretion.

Short-term alcohol administration alters KiSS-1 gene expression in the reproductive hypothalamus of prepubertal female rats

BACKGROUND

Kisspeptins bind to the G-protein-coupled receptor (GPR54) to activate hypothalamic luteinizing hormone releasing hormone (LHRH) secretion at the time of puberty. Alcohol (ALC) causes depressed prepubertal LHRH release, resulting in depressed luteinizing hormone (LH) secretion and delayed puberty. Because KiSS-1 and GPR54 are important to the onset of puberty, we assessed the effects of chronic ALC administration on basal expression of these puberty-related genes within the reproductive hypothalamus, as well as hormones and transduction signaling pathways contributing to their activity.

METHODS

Immature female rats were fed a liquid diet containing ALC for 6 days beginning when 27 days old. Controls received either companion isocaloric liquid diet or rat chow and water. Animals were decapitated on day 33, in the late juvenile stage of development. Blood was collected for the assessment of serum hormone levels. Brain tissues containing the anteroventral periventricular (AVPV) and arcuate (ARC) nuclei were obtained for assessing expression of specific puberty-related genes and proteins.

RESULTS

KiSS-1 mRNA levels in the AVPV and ARC nuclei were suppressed (p < 0.001) in the ALC-treated rats. GPR54 gene and protein expressions were both modestly increased (p < 0.05) in AVPV nucleus, but not in ARC nucleus. Alcohol exposure also resulted in suppressed serum levels of insulin-like growth factor-1 (IGF-1), LH, and estradiol (E(2)). As IGF-1, in the presence of E(2), can induce expression of the KiSS-1 gene, we assessed the potential for ALC to alter IGF-1 signaling in the reproductive hypothalamus. IGF-1 receptor gene and protein expressions were not altered. However, protein expression of phosphorylated Akt, a transduction signal used by IGF-1, was suppressed in the AVPV (p < 0.05) and ARC (p < 0.01) nuclei.

CONCLUSIONS

Alcohol causes suppressed KiSS-1 gene expression in the reproductive hypothalamus; hence, contributing to this drug's ability to cause suppressed LHRH secretion and disruption of the pubertal process. We suggest that this action, at least in part, is through altered IGF-1 signaling.

Effect of neurogenic stress and ethanol on nitric oxide synthase and cyclooxygenase activities in rat adrenals

Repeated restraint stress (RRS) in male rats activated the pituitary adrenal system, as indicated by increases in adrenal weight and plasma corticosterone concentration that were accompanied by a decrease in constitutive nitric oxide synthase (cNOS), but not inducible NOS (iNOS). iNOS activated cyclooxgenase, causing elevated prostaglandin E(2) (PGE(2)) and F(2 alpha) in the adrenals, but had no effect on lipoxygenase. Administration of ethanol (ETOH) was also associated with elevated adrenal weight and a slight increase in corticosterone coupled with a decrease in both cNOS and iNOS and PGs in the adrenal. When ETOH was administered together with RRS, a decrease in iNOS and PGE release was noted consequent to a reduction in iNOS. Thus, ETOH probably reduced RRS-induced adrenocorticotropic hormone release. Adrenals were incubated in vitro to further evaluate the role of NO in these processes. Results indicated that NO released by sodium nitroprusside increased corticosterone release presumably by activating guanylyl cyclase with production of cyclic guanosine monophosphate (cGMP), because although NO also increased PGE release, PGE(2) (10(-5)-10(-9) M) decreased corticosterone release, an effect that was highly significant at a concentration of 10(-7) M PGE(2). ETOH (100 mM) had no effect on corticosterone release and did not block the increase in corticosterone caused by NO; however, ETOH reduced PGE release into the medium and blocked PGE(2) release induced by NO. Consequently, NO activated corticosterone release not by PGs, but by activation of guanylyl cyclase and release of cGMP. PGs have a negative feedback to suppress corticosterone release.

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.

Neuronal degeneration in rat cerebrocortical and olfactory regions during subchronic "binge" intoxication with ethanol: possible explanation for olfactory deficits in alcoholics

Severe, repetitive ("binge") ethanol intoxication in adult rats (intragastric delivery 3 times daily for 4 days in a modification of the Majchrowicz method) precipitates neuronal degeneration in selected cerebral cortical regions involved in memory and olfaction, confirming the results of Switzer and colleagues (Anat. Rec. 202: 186a, 1982). Neuronal damage was visualized with the de Olmos cupric silver technique for degenerating neurons and processes (argyrophilia), and was quantitated by total counts and densities of argyrophilic cells/fields. The specificity of the degeneration provides a neuropathological basis for the olfactory memory deficits in chronic alcoholics. In highly intoxicated rats, argyrophilia was most extensive among hippocampal dentate gyrus granule cells, pyramidal neurons in layer 3 of the entorhinal cortex, and olfactory nerve terminals in the olfactory bulb. Degenerating pyramidal neurons were also consistently seen in the insular cortex and olfactory cortical regions, such as the piriform and perirhinal cortices. There were few argyrophilic neurons in the CA regions of the hippocampus and none in the cerebellum--regions generally shown to have cell loss in long-term ethanol feeding models--but degenerating mossy fibers in the CA2 region were observed. Degeneration was maximal before the peak period of abstinence symptoms in this model, because argyrophilic densities were no greater 36 hr, compared with 8 hr after the last ethanol dose. High blood ethanol levels were required, because argyrophilia, absent from isocaloric controls, also was only evident in ethanol-intoxicated rats with mean blood ethanol levels for days 2 to 4 above 300 mg/dl; however, it increased substantially between 350 and 550 mg/dl. The resemblance of the argyrophilic distribution to the regional neuropathology that occurs in experimental seizures indicates that the ethanol-induced degeneration may have an excitotoxic basis. Progressive reductions in the seizure threshold (e.g., kindling phenomena that have been documented during binge ethanol intoxication) might be associated with excitotoxic hyperactivity during the repetitive nadirs between high blood and brain ethanol peaks. However, direct toxic actions of ethanol or its metabolites could also be involved. Overall, the model should be useful for studying mechanisms of ethanol-induced selective cortical and olfactory brain damage.

Effect of ethanol on the synthesis of insulin-like growth factor 1 (IGF-1) and the IGF-1 receptor in late prepubertal female rats: a correlation with serum IGF-1

For several years, it has been well accepted that insulin-like growth factor 1 (IGF-1) plays a critical role in peripubertal growth. Recently, we have provided evidence to suggest that this peptide may also be involved in the sexual maturation process, via an action to stimulate hypothalamic luteinizing hormone releasing hormone release. Because ethanol (ETOH) delays puberty, an event that is associated with depressed growth rates and decreased growth hormone and luteinizing hormone (LH) secretion via actions at the hypothalamic level, we investigated whether this drug is capable of altering the expression of genes encoding IGF-1 in liver and brain, as well as the expression of the type 1 IGF receptor (IGF-1R) within the median eminence (ME). Also, we wanted to determine if any regional changes in the expression of these genes were associated with concomitant alterations in the serum levels of IGF-1 and LH. Rats were implanted with gastric cannulae on day 24 and began receiving specific control or ETOH diets on day 29. Rats were killed on day 34, determined to be in the late juvenile stage of development, and their tissues and blood were collected. Results indicate that the ETOH-fed rats showed a decrease (p < 0.01) in the expression of hepatic IGF-1 mRNA when compared with the controls, and this paralleled depressions in both serum IGF-1 (p < 0.01) and LH (p < 0.01). In contrast, no changes were detected in IGF-1 mRNA expression in the preoptic area and hypothalamus, as well as in IGF-1R mRNA expression within the ME. These results suggest that the well-known detrimental effects of ETOH on growth rates and the progression of the female pubertal process in the rat may be associated with the drug's ability to depress the hepatic synthesis of IGF-1 and the subsequent prepubertal circulating levels of the protein.

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.

Ethanol acutely reduces LH and prolactin secretion: possible involvement by dopamine

Ethanol (ETOH) administered acutely to castrate male rats caused a decline in pituitary luteinizing hormone (LH) and prolactin (PRL) secretion. This was associated with an elevation in hypothalamic and median eminence stores of dopamine (DA) that was related to the dose of alcohol given. Pituitary stalk transection (PST) resulted in a significant rise in plasma PRL levels compared to sham control animals, which suggests that DA in the hypophysial portal blood exerted an inhibitory influence on pituitary PRL secretion. The DA agonist bromocriptine failed to alter mean plasma LH levels in stalk-transected rats. The ETOH-treated castrated rats showed a significant rise in circulating PRL after injection of the DA receptor antagonist haloperidol metabolite II (HAL), but the administration of the DA receptor agonist R(-)-apomorphine HCL (APO) caused plasma PRL to decline to near undetectable levels. Plasma LH levels remained unchanged in the HAL- and APO-treated rats and were similar to those of sham controls. These results suggest that lactotroph DA receptors were still functional. Thus our previous finding of ETOH-induced reduction on LH secretion may be attributable to an inhibitory effect by DA on the luteinizing hormone-releasing hormone (LHRH) peptidergic neurons rather than a direct inhibition by DA on the pituitary gonadotroph.

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.

Alcohol inhibition of suckling-induced prolactin release in lactating rats: threshold evaluation

Prolactin release in response to suckling was examined in primiparous lactating rats two hours after alcohol administration. Litters were adjusted to eight pups on lactation day 2 and dams were implanted with an atrial catheter on day 6. On day 10, pups were separated from the mother at 0800 h. An extension was attached to the catheter at 1100 h. Following removal of a baseline blood sample an hour later, rats were infused with alcohol doses of 0, 0.5, 1.0, 2.0 or 2.5 g/kg body weight. Two hours later, pups were returned to dams. Subsequent blood samples were obtained 10, 30, 60, 120 and 180 min after the onset of suckling. Following 10 min of suckling, plasma prolactin for groups of rats infused with alcohol at 2.0 and 2.5 g/kg body weight were lower than control, 0.5 and 1.0 g/kg groups. The blood alcohol level (BAL) for the 2.0 g/kg group was 94 +/- 8 mg% and for the 2.5 g/kg group was 162 +/- 4 mg%. After 30 min, the BAL for the 2.5 g/kg group was 134 +/- 5 mg% and plasma prolactin was suppressed in this group compared to control, 0.5 and 1.0 g/kg groups. The BAL for the 2.0 g/kg group after 30 min of suckling was 74 +/- 9 mg% but prolactin was not significantly lower than controls. We conclude that in rats, alcohol inhibition of suckling-induced prolactin release is directly correlated to the BAL. The threshold BAL which effectively inhibits this prolactin release is lower than the human legal intoxication level.

Pattern and duration of the inhibitory effect of alcohol administered acutely on suckling-induced prolactin in lactating rats

We have characterized the pattern and duration of the inhibitory effect of acute alcohol administration on suckling-induced prolactin (PRL) release in the lactating rat. On day 2 of lactation, litters were adjusted to eight pups. On day 6, dams were implanted with an atrial catheter and experiments were conducted on day 10 of lactation. Pups were removed from the dams at 0800 hr. An extension tube filled with heparinized saline was attached to the catheter at 1300 hr. At 1400 hr, a preinfusion (PRE 0) blood sample was removed and was followed by infusion of saline (control) or alcohol in saline (0.5, 1.0, 2.0, 2.5 g/kg body weight doses) solutions. Following the removal of a postinfusion (POST 0) blood sample, pups were returned to the mother. Subsequent blood samples were obtained 10, 30, 60, 120, and 180 min after initiation of suckling. In separate groups, the effects of alcohol on basal PRL were studied by collecting blood samples PRE 0, POST 0 and 20, 40, 60, 80, 100, and 120 min following infusion of saline or alcohol in saline to lactating rats also separated from their pups for 6 hr. Alcohol infusion did not alter basal PRL. However, suckling-induced PRL was inhibited at 10, 30, 60, and 120 min of suckling by alcohol administered at doses greater than or equal to 1.0 g/kg body weight. After 180 min of suckling, plasma PRL levels were comparable among groups. The suckling latency for the 2.5 g/kg body weight alcohol group was greater than for other groups, but the quantities of milk consumed during the 3-hr suckling period were comparable.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute alcohol infusion does not alter plasma gonadotropins or prolactin in ovariectomized rats

We examined the effects of acute alcohol on basal plasma FSH, LH, and prolactin in ovariectomized rats. Alcohol infusion and blood sampling were done via an indwelling atrial catheter. Blood samples for alcohol and hormone determinations were collected before, and 5 to 120 min after completion of saline (control) or alcohol in saline (experimental) infusion. Plasma follicle-stimulating hormone, luteinizing hormone, and prolactin were not altered during the 2-hr period. Peak blood alcohol concentrations achieved following 1.0- and 2.0-g/kg body weight of alcohol doses were approximately equal to, and twice, the legal human intoxication levels, respectively. Alcohol clearance rates from blood for the two groups were: 130 +/- 3 mg/kg/hr for the 1.0-g/kg body weight group and 151 +/- 3 mg/kg/hr for the 2.0-g/kg body weight group. These results show that acute alcohol does not affect basal gonadotropins and prolactin secretion in ovariectomized rats.

Actions of ethanol on hypothalamic and pituitary hormones in prepubertal female rats

To determine the effects of prepubertal ethanol (ETOH) exposure on hypothalamic and pituitary hormones known to be involved in the onset of female puberty, we have chronically exposed female rats to either a liquid-diet containing ETOH or an isocaloric control liquid-diet. An additional set of controls consisted of animals maintained on Lab Chow, and water provided ad lib. Our results indicate that the feeding regimen employed produced no differences with regard to body and reproductive organ weights, as well as any of the hormones measured between the two control groups. Conversely, ETOH-treated animals showed significantly lower body and reproductive organ weights than the control animals and although no differences were detected between ETOH-treated and control animals with regard to the hypothalamic content of somatostatin (SRIF), there was a significant increase in the hypothalamic content of growth hormone releasing hormone (GHRH), with a concomitant and significant decrease in the serum concentration of growth hormone (GH). Furthermore, the ETOH-treated animals showed a significant increase in the hypothalamic content of luteinizing hormone releasing hormone (LHRH) with a significant decrease in the serum concentration of luteinizing hormone (LH), but not follicle stimulating hormone (FSH). These results demonstrate for the first time that chronic, prepubertal ETOH administration alters the concentrations of specific hypothalamic and pituitary hormones which are known to be involved in the female pubertal process.

Alcohol inhibits suckling-induced prolactin release and milk yield

The effects of acute administration of alcohol on suckling-induced prolactin (PRL) release and milk yield were studied in primiparous lactating rats. On lactation day 2, pups were culled to 8 per litter. On day 5, dams were implanted with atrial catheters. On day 10, pups were separated from the dams at 0900 hr; at 1300 hr, an extension containing heparin (50 IU/ml) and 0.9% saline was attached to the exteriorized portion of the catheter. At 1400 hr, 0.4 ml blood was removed and replaced with 0.9% saline (control) or 0.3, 0.5 or 1.0 g/kg body weight of alcohol. At 1500 hr a second blood sample was obtained followed by a second alcohol or saline infusion. Pups were returned to dams and blood samples were obtained 10, 30, and 60 min after suckling. Milk consumption was calculated by weighing pups before and after 60 min of suckling. PRL in plasma samples was measured by radioimmunoassay. Alcohol did not alter baseline serum PRL. However, suckling-induced PRL release and milk consumption by the pups were significantly inhibited. Since basal PRL was not altered following administration of alcohol, the inhibitory effect of alcohol on suckling-induced PRL release is attributed to a disruption of transmission of the impulse arising from suckling stimulus.

Ethanol and the pulsatile release of luteinizing hormone, follicle stimulating hormone and prolactin in ovariectomized rats

Conscious ovariectomized rats were administered either saline or an ethanol (ETOH)-saline solution via a permanent intragastric cannula, and plasma LH, FSH and PRL were measured by RIA of jugular blood samples drawn every 10 min through an indwelling silastic catheter. Control injections of saline into the gastric cannula did not modify any of the plasma hormone concentrations. Animals which were administered ETOH, showed marked decreases in the plasma concentrations of LH. Compared to basal levels, a significant decrease in the area under the secretion curve of LH occurred during the initial hour after ETOH administration. This decline continued with the lowest levels of plasma LH being detected at approximately 1.5 hours following the ETOH injection. Additionally, no LH pulses were detected in any of the ETOH-treated animals during the second hour after ETOH; thus, reducing the number of LH pulses observed in ETOH vs. saline-injected animals. Comparable increases in the area under the LH curve occurred following a challenge dose of LHRH in both saline and ETOH-injected rats, indicating that pituitary responsiveness was the same for both groups. In contrast to LH, ETOH did not significantly alter the pattern of FSH secretion, as represented by the area under the curve and the number of FSH pulses. In addition to the differential effects of ETOH on the pulsatile release of LH and FSH, the present data also indicate that these two gonadotropins have different secretory patterns. With regard to PRL, ETOH-injected animals showed a significant elevation in plasma PRL levels during the first hour following ETOH administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of ethanol on luteinizing hormone, follicle stimulating hormone and prolactin secretion in the female rat

Serum luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (Prl) levels were determined in ovariectomized rats following short-term (3 day) ethanol (ETOH) administration. ETOH was given either as an ETOH-saline solution, or via a liquid diet regimen (Bio-Serve, Inc.). Rats receiving the ETOH-saline solution (3.0 g ETOH/kg) were injected via a permanent gastric cannula every 8 hr for 3 consecutive days, while control animals received injections of saline only. Each animal receiving the liquid diet regimen was provided with 40 ml of the ETOH or the isocaloric control diet ad lib during the lights-off period, followed by 40 ml of the respective diet via the gastric cannula (4 injections of 10 ml each) equally divided over the lights-on period. Additional control animals were cannulated and maintained on Lab Chow and water, but were left untreated. Both groups of ETOH-treated rats had significantly lower serum LH levels with significantly higher Prl levels when compared to values in their respective control animals. By contrast, ETOH failed to alter FSH levels. These data indicate that ETOH can differentially affect LH, FSH, and Prl secretion following short-term ETOH exposure. The dissociation observed between LH and FSH secretion following ETOH supports the hypothesis that there are separate hypothalamic control mechanisms for LH and FSH secretion.