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

Efeitos de bebidas alcóolicas em mães lactantes e suas repercussões na prole

Foi feita uma revisão de estudos sobre os efeitos ocasionados pelo consumo de bebidas alcóolicas por lactantes, analisando os múltiplos distúrbios metabólicos, nutricionais e psicológicos evidenciados no organismo materno e dos recém-nascidos. É enfatizada a necessidade de orientações clínico-nutricionais nos serviços de pré-natal e puericultura acerca dos riscos da ingestão de bebidas alcoólicas em qualquer quantidade, por mães no período de gestação e aleitamento.

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.

Infant rats respond differently to alcohol after nursing from an alcohol-intoxicated dam

Our previous studies indicate that rat pups are able to detect the low levels of ethanol (175 mg %) found in the milk of a moderately intoxicated dam. The present study tested the effect of infantile interactions (including suckling) with ethanol-treated mothers on later behavioral responsiveness to ethanol's sensory properties. In Experiment 1, pups suckled from dams subjected to a 2.5 g/kg ethanol dose (i.g.) or water-treated females during postnatal days (PDs) 3, 5, 7, 9, 11, and 13. During PD 15, these pups were exposed to procedures to induce a conditioned aversion to the low level of ethanol (175 mg % in water), with lithium chloride as the unconditioned stimulus. Conditioning was more effective for pups with the prior ethanol experience within the nursing context. Greater responsiveness to ethanol in milk also was found for conditioning control pups that had interacted with intoxicated dams than for those that had interacted with water-treated dams. Experiment 2 determined that interaction with an intoxicated dam was sufficient for altered responsiveness to ethanol, in that the additional conditioning procedures of Experiment 1 were not needed for the effect. Generally, a relatively brief history of infantile interaction with ethanol-intoxicated dams increased later responsiveness to ethanol's orosensory properties. The results suggest that moderately intoxicated dams within the nursing context provide information to the progeny that may lead to the establishment of ethanol-related memories.

Prolactin secretion in lactating rats following chronic alcohol exposure: provocative tests with secretagogues

This study was done to examine the mechanism of action of alcohol in inhibiting suckling-induced prolactin release in the lactating rat. Alcohol (0.0, 1.0 or 2.0 g/kg body weight) was administered daily for 8 days from day 5 to 12 of lactation via an indwelling atrial catheter, implanted on day 3 of lactation. Following the administration of the initial alcohol dose, infusion was continued at rates required to maintain the blood alcohol levels (BALs) for four hours every day. Prolactin responses to sulpiride and TRH were tested on day 12. Alcohol administration for 8 days and maintaining the blood alcohol levels for four hours daily did not affect the basal or sulpiride and TRH-stimulated plasma prolactin release. Since the prolactin releasing capacity of pituitary lactotropes of the lactating rat is not compromised following chronic alcohol exposure, we conclude that alcohol does not act at the anterior pituitary level to inhibit the suckling induced prolactin release but probably acts by other mechanisms: either via the hypothalamic and/or higher central nervous system or by disrupting the neural impulse transmission, engendered at the nipples in response to suckling.

Effects of chronic alcohol administration on lactational performance in the rat

Lactating rats, with litters adjusted to eight pups on day 2, were implanted with an atrial catheter on day 3 of lactation. Alcohol in doses of 0.0, 1.0, or 2.0 g/kg BW was infused from day 5 to 12. The blood alcohol levels (BALs) achieved following infusion of the initial doses were maintained for 4 hours daily by infusion. To control for the reduced food intake in alcohol administered groups, rats receiving alcohol doses of 0.0 and 1.0 g/kg BW were pairfed to 2.0 g/kg BW alcohol group. For infusion, combinations of 50% dextrose, 30% alcohol in saline and saline solutions were used for 0.0 and 1.0 g/kg BW alcohol groups whereas the 2.0 g/kg BW alcohol group received 30% alcohol in saline thereby equilizing the calorie intake of the three experimental groups. On day 12, pups were separated from the dams at 0800 h, a catheter extension was attached at 0900 h and baseline blood samples for prolactin level were taken at 1000 h. Following infusion of initial alcohol doses, samples were taken for BALs. Additional samples for BALs were removed 2 h after continuing the infusion. At the end of 4-h infusion, blood samples were taken for alcohol and postinfusion prolactin levels. In groups designed to study the suckling-induced prolactin release, pups were weighed and returned to the dams. Subsequent blood samples were taken 30 min after initiation of suckling. In nonsuckled groups, blood samples were obtained at corresponding time periods. BALs were determined by head space gas chromatography and plasma prolactin by a double antibody radioimmunoassay. Suckling latency and milk consumption during the 30 min of suckling were measured. Dams' and litter weights were determined on days 2, 5, and 12 of lactation. Infusion of alcohol for 8 days from day 5 to 12 of lactation did not affect maternal body weight. However, litters nursed by dams receiving 2.0 g/kg BW alcohol weighted less on day 12 compared to all other groups. Suckling latencies did not differ among groups. Milk consumed during the 30 min of suckling was lower for the alcohol administered groups. The inhibitory effect on milk consumption was greater for the 2.0 g/kg BW group than in the 1.0 g/kg BW alcohol group. Alcohol infusion did not affect the basal prolactin, whereas, the higher dose (2.0 g/kg BW) inhibited suckling-induced prolactin release.(ABSTRACT TRUNCATED AT 400 WORDS)

Attenuation of the magnitude of suckling-induced prolactin release with advancing lactation: mechanisms

To study why suckling-induced plasma prolactin levels decline in magnitude with advancing lactation, we examined prolactin release in lactating rats following suckling and pharmacologic manipulations during early, mid- and late lactation. On day 2 of lactation, litters were adjusted to 8 pups. On day 3, dams were implanted with an atrial catheter and experiments were conducted on lactation days 5, 11 and 17. To examine suckling-induced prolactin release, pups were removed at 0800 h, an extension was attached to the catheter at 1100 h, and pups returned to dams at 1200 h. Blood samples were obtained before, and at 10, 30, 60, 90 and 120 min after suckling started. Prolactin responses to sulpiride and thyrotropin releasing hormone (TRH) administration were studied in lactating rats separated from their litters for 4 hours. Blood samples were obtained before, and at 10, 30, 60 and 90 min after sulpiride (10 or 40 micrograms/kg BW) and 5, 10, 20 and 30 min after TRH (1 or 4 micrograms/kg BW) in rats pretreated with sulpiride. Prolactin release in response to suckling, administration of sulpiride or sulpiride and TRH diminished as lactation advanced. From these results, we conclude that refractoriness in anterior pituitary lactrotropes to prolactin-releasing stimuli is at least partially responsible for the decline in suckling-induced prolactin release with advancing lactation.

Beta-endorphin-stimulated prolactin release in lactating rats following alcohol administration

To delineate the mechanism of alcohol inhibition of the suckling-induced prolactin increase, we examined beta-endorphin-stimulated prolactin release in lactating rats separated from their litters. On day 2 of lactation litters were adjusted to eight pups. On day 7, dams were implanted with an atrial catheter; experiments were conducted on lactation day 10. Litters were separated from their dams at 0800. After five hours, a PE50 extension tube filled with heparinized saline was attached to the catheter. At 1400 a preinfusion blood sample was removed and was followed by infusion of saline (control) or alcohol in saline (1.0 and 2.0 g/kg/body weight). Following the removal of a postinfusion blood sample, beta-endorphin (600 micrograms/kg/body weight) was administered. Additional blood samples were withdrawn 10, 30, 60, and 120 min after beta-endorphin. Alcohol infusion did not alter basal prolactin. beta-Endorphin administration resulted in pronounced prolactin increases in all groups. Alcohol failed to inhibit beta-endorphin-induced plasma prolactin increase. From the present study with beta-endorphin and our previous studies with sulpiride and thyrotropin-releasing hormone (TRH) it is concluded that the anterior pituitary is not the site where alcohol acts to inhibit suckling-induced prolactin release in rats.

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.