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)     

Lactation and Prolactin Release in Foster Dams Suckling Prenatally Ethanol Exposed Pups

The effect of prenatal ethanol exposure on lactation was studied employing prenatally ethanol-exposed pups transferred to foster dams following parturition. During pregnancy, from day 8 to term, dams consumed either standard laboratory chow (ad libitum control), or liquid diets containing 0%, 17.5%, or 35% ethanol derived calories (EDC). To equalize caloric intake, the 0% and 17.5% EDC groups were pair-fed to rats in 35% EDC group. Following delivery, pups born to dams fed with laboratory chow (control) or liquid diets containing 0, 17.5, or 35% EDC were adjusted to eight per litter and transferred to foster dams, which had been fed laboratory chow and water ad libitum throughout pregnancy. Foster dams were implanted with an atrial catheter on day 3 of lactation. On days 6 (early lactation) and 10 (midlactation), following separation of litters from dams for a 6-hr period, a baseline blood sample was removed via a catheter extension. Pups were weighed and returned to the dams. Subsequent blood samples were obtained 10, 30, 60, 120, and 180 min after initiation of suckling. Suckling latency and the amount of milk consumed during the 3-hr suckling were also determined. Litters were weighed on days 2, 6, 10, and 21. The prolactin surge in foster dams in response to suckling by prenatally ethanol-exposed pups was not altered on day 6 of lactation. On day 10, after the initial rise, suckling-induced prolactin was amplified in dams suckled by prenatally ethanol-exposed pups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence that exteroceptive stimuli other than suckling have no major effect on plasma prolactin in lactating rats

The ability of exteroceptive stimuli from pups to increase plasma prolactin in lactating dams was investigated. Prolactin profiles were measured during 30 min of suckling followed by complete or partial separation from pups. Prolactin profiles were also measured subsequent to complete or partial isolation from pups in dams which had been with pups permanently before the experiment. In addition, plasma prolactin was measured in dams which after a night of isolation were partially united with pups. Finally, the effect of ether stress on prolactin profiles after interruption of suckling by pups was determined. Vigorous suckling after a period of isolation induced a sharp increase of plasma prolactin. Subsequent to pup removal, either partial or complete, prolactin profiles showed a widespread variation. Also dams which before experimentation were kept permanently with pups, showed a great variation in prolactin profiles subsequent to either complete or partial separation from pups. Plasma prolactin either decreased rapidly or gradually. In several dams a rapid or a gradual decline of plasma prolactin was interrupted by one or more episodes of prolactin release. Partial reunion with pups after a night of isolation, either in mid-lactation or in late lactation, did not induce a rise of plasma prolactin. It is concluded that exteroceptive stimuli from pups are not effective as prolactin releasing signal. Because ether stress did not induce a steep rise of plasma prolactin, we conclude that the episodic rises of plasma prolactin in dams, subsequent to partial or complete removal of pups, are due to spontaneous activity of the hypothalamo-pituitary system.     

Effects of Levamisole on Ethanol-Induced Suppression of Lactational Immune Transfer in Rats

Maternal ethanol consumption in rats has been shown to inhibit lactational transfer of immunity to Trichinella spiralis (T. spiralis) from dams to their neonates. The purpose of this study was to determine if this depressed immune transfer could be altered by treating the dams with a known immunostimulatory drug during pregnancy and lactation. Groups of female rats were fed ethanol-containing or were pair-fed isocaloric control liquid diets for 30 days, infected orally with 1,000 T. spiralis larva, and then continued on diet for 10 days to allow the adult worms to establish. The animals were placed on chow diets (maximum 5 days) and mated 1 to 1 with males. On day 1 of pregnancy the animals were returned to their respective liquid diets through pregnancy and lactation. One-half of the ethanol-treated animals was given 15 mg/kg body weight of levamisole in the diet beginning on day 10 of pregnancy and continuing until day 17 of lactation. On day 19 of lactation, pups from all experimental groups were challenged orally with 200 T. spiralis larva, and killed at 3 or 8 days postchallenge. Assays for intestinal worm burdens, IgG anti-T. spiralis serum antibodies, and mesenteric lymph node cell proliferation were conducted. At both sacrifice periods, pups from ethanol-treated animals showed significantly higher intestinal worm counts (decreased immunity) and significantly lower titers of specific antibodies than the pups of pair-fed animals or pups of animals receiving levamisole in addition to ethanol. There were no differences between pups of the ethanol/levamisole dams and pair-fed dams in worm counts or antibody titers. No differences in mesenteric lymph node cell proliferation in response to T. spiralis antigen or to concanavalin A was observed between the three groups. These results indicate that administration of levamisole to ethanol-induced, immunosuppressed dams can reverse some of the deleterious effects normally seen in lactational immune transfer to suckling pups.     

Disruption of maternal behavior by alcohol intoxication in the lactating rat: a behavioral and metabolic analysis

BACKGROUND: Preweanling rats exhibit clear behavioral signs of distress after interacting with an alcohol-intoxicated dam. Interestingly, behavioral reactivity of infants to the experience of alcohol in the nursing context decreases as a function of repeated alcohol administrations to the mother. In this study, maternal activities were examined when dams were exposed to repeated administrations of a subnarcoleptic alcohol dose. Maternal changes in alcohol metabolism were also analyzed as a function of repeated exposures to the drug. METHODS: During postpartum days 3, 5, 7, 9, 11, and 13, nursing dams received an intragastric administration of either 2.5 g/kg of alcohol or water. Maternal behaviors were evaluated (experiment 1). Blood alcohol levels (BALs) of the dams were determined on postpartum day 16 after all mothers received either an intragastric (experiment 2) or an intraperitoneal (experiment 3) dose of alcohol. The doses used (2.5 g/kg intragastrically and 1.5 g/kg intraperitoneally) were chosen because they promote similar peak BALs in dams naive to alcohol. RESULTS: Maternal behaviors were strongly affected by the state of intoxication. Nevertheless, these disruptions clearly subsided with progression of alcohol-related experiences (experiment 1). Chromatographic analysis of alcohol metabolism indicated the development of tolerance in dams that had prior experience with alcohol (experiment 2). Changes in BALs as a function of prior experience with alcohol seemed related to first-pass alcohol metabolism rather than hepatic oxidative processes of the drug (experiments 2 and 3). CONCLUSIONS: When the dam first experiences a moderate state of alcohol intoxication, maternal behaviors are uniformly disrupted. Subsequent exposures to alcohol lead to maternal metabolic tolerance. In conjunction with previous studies, these data indicate that infantile reactivity to alcohol is dependent on how the members of the dam/pup dyad express or perceive ethanol's postabsorptive effects.     

Experimental manipulations of prolactin following removal of pouch young or bromocriptine treatment during lactational quiescence in the Bennett's wallaby

Experiments were conducted to investigate whether prolactin suppresses the corpus luteum during lactational quiescence in the Bennett's wallaby. In the first experiment, pouch young were removed from lactating wallabies (day 0) which were then treated daily for 7 days with either saline, or 8 mg domperidone or 2 mg ovine prolactin. In the saline-injected animals there was a transient peak in progesterone concentrations on day 4 and birth on day 28. The transient progesterone peak and births were significantly (P less than 0.01) delayed by 5 and 8 days in animals treated with domperidone and ovine prolactin respectively. In the second experiment, four groups of lactating wallabies were treated on day 0 with either 60 mg bromocriptine (groups C and D) or the vehicle (groups A and B). On days 0-6, groups B and D were injected daily with 2 mg ovine prolactin while groups A and C received the vehicle. In group C, three pouch young died 14-29 days after administration of bromocriptine, and there was a transient rise in progesterone on day 4 in all animals, indicating that bromocriptine resulted in immediate reactivation of the quiescent corpus luteum. New births occurred in two animals on day 28. In group D, which received bromocriptine followed by ovine prolactin for 7 days, all the original pouch young remained alive at the end of the experiment. Four of the animals from this group showed a transient progesterone peak on day 11, with births in two animals on days 35 and 36 indicating that the effects of bromocriptine were prevented whilst ovine prolactin was being administered.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanisms responsible for suppression of FSH and LH during lactation in the rat

Mechanisms responsible for suppression of FSH and LH secretion during lactation were investigated in rats, with special reference to the suckling stimulus and ovarian inhibin. Concentrations of immunoreactive inhibin in the peripheral plasma and bioactive inhibin in ovarian venous plasma were always low on days 3 and 5 of lactation in dams nursing eight pups, whereas values were always high on days 17 and 20 of lactation in dams nursing eight pups and on day 5 of lactation in dams nursing two pups. There was an FSH surge within 48 h after removal of litters on days 3 and 5 of lactation in dams nursing eight pups, whereas plasma concentrations of FSH were unchanged within 48 h by removal of litters on days 17 and 20 of lactation in dams nursing eight pups and on day 5 of lactation in dams nursing two pups. Plasma LH concentrations increased significantly compared with those of control animals within 24 h after removal of the litter on any day of lactation, regardless of the litter size. Plasma FSH levels increased within 6 h after bilateral or unilateral ovariectomy in lactating rats only on the days when plasma concentrations of inhibin were high before ovariectomy, such as day 17 of lactation in dams nursing eight pups and on day 5 of lactation in dams nursing two pups, whereas the mean concentrations of plasma LH showed no significant increase within 12 h after bilateral ovariectomy in these lactating rats. Treatment with progesterone or oestradiol-17 beta after unilateral ovariectomy did not inhibit the increase in plasma FSH levels, while the increase in plasma concentrations of FSH after surgery was completely inhibited by injecting inhibin (porcine follicular fluid). Treatment with steroid hormones inhibited the basal levels of LH in unilateral ovariectomized lactating rats. Plasma FSH concentrations increased sharply within 6 h after a single i.v. injection of anti-inhibin serum on days 10, 15 and 20 of lactation in dams nursing eight pups and on day 5 of lactation in dams nursing two pups, whereas only a small but significant increase in concentrations of FSH was noted 6 h after the antiserum treatment on day 5 of lactation in dams nursing eight pups. Concentrations of plasma LH were unchanged by treatment with antiserum in lactating rats throughout lactation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Neonatal activation of alcohol-related prenatal memories: impact on the first suckling response

BACKGROUND: Rat fetuses seem to be capable of associative learning mediated through alcohol's unconditioned properties. The newborn's suckling response immediately after birth is dependent on olfactory stimuli present in the fetal milieu and/or odorants perceived immediately after birth. The present study analyzed the impact of olfactory fetal learning supported by maternal-fetal alcohol intoxication on the newborn's first postnatal suckling response, in the presence or absence of chemosensory cues originally associated with alcohol during prenatal life. METHODS: During gestational days 17 to 20, fetuses experienced a salient novel cue (cineole) explicitly paired or not with the induction of alcohol intoxication resulting from maternal intragastric intubation of a 2 g/kg ethanol dose. A separate set of dams were intubated with only water. In experiment 1, cesarean-delivered pups were tested shortly after birth for their response to a surrogate nutritive nipple scented with cineole or with no explicit odor. In experiment 2, pups were similarly evaluated after the prenatal treatment when cineole, a novel odorant (lemon), or no explicit odor was presented either in conjunction with the nipple or before being tested with the nipple. RESULTS: In both experiments, fetal olfactory conditioning supported by alcohol intoxication had a significant effect on the newborn's first suckling episode, depending on the olfactory cues presented before or during suckling. Presence of cineole but not of novel odorants seemed to activate the associative memory acquired in utero. Once the memory was activated, pups that were subjected to fetal odor-alcohol pairings were found to attach significantly more to surrogate nutritive nipples than did fetal control animals. CONCLUSIONS: Prenatal experience with alcohol intoxication can result in chemosensory associative learning mediated by the drug's postabsorptive effects. This learning determines attachment patterns of newborns when they reexperience olfactory cues that had signaled onset of the state of acute alcohol intoxication when they were fetuses. Considered in view of previous experiments, the present results generate two alternative hypotheses relative to the affective component of the memory established in utero: (1) alcohol intoxication is an appetitive reinforcer during fetal life, or (2) the calming effects of postnatal suckling behavior counteract negative hedonic components of the memory accrued in utero.     

The role of prolactin in the luteotrophic process of lactating rats.

Treatment of pseudopregnant rats with ergocryptine mesylate (ECR) depressed serum prolactin levels but had no apparent effect on LH secretion. Ovarian progesterone secretion was significantly, reduced 24 hr after ECR treatment on day 6 or 9 of pseudopregnancy and the secretion rate of 20alpha-OH-P remained constant. When lactating rats nursing 6 pups were treated with ECR on day 6 or 9 postpartum, progesterone secretion was significantly decreased by 48 hr after treatment and 20 alpha-OH-P secretion was not altered. Furthermore, ECR inhibited litter weight gains of these lactating dams. After treatment of normal pregnant and pregnant lactating rats with ECR on day 6 of pregnancy, gestation was terminated in all animals. If ECR was given on day 9 to normal pregnant rats, to pregnant lactating animals whose pups were removed on day 9 postpartum, or to pregnant lactating rats treated with LH, gestation was not terminated. However, treatment with ECR of day 9 pregnant lactating rats whose pups continued to suckle terminated pregnancy in 13 of 21 animals. The results of these studies suggest the elevated pituitary prolactin secretion is necessary for maintenance of luteal function in pseudopregnant and lactating rats, and in pregnant lactating rats elevated pituitary prolactin secretion is a component of the luteotrophic complex for a longer period of time than in normal pregnant rats.     

Regulation by endogenous opioids of suckling-induced prolactin secretion in pregnant and lactating rats: role of ovarian steroids

Evidence suggests that endogenous opioid peptides are implicated in the suckling-induced prolactin rise. We explored the role of the opioid system and the participation of ovarian hormones in the regulation of prolactin induced by the suckling stimulus at the end of pregnancy in rats with developed maternal behavior, and during lactation. Suckling for 24 h induced a significant increase in serum prolactin on day 19 of pregnancy, which was increased more than three times when naloxone (2 mg/kg s.c.) or mifepristone (2 mg/kg) was administered. The combination of naloxone and mifepristone did not increase serum prolactin more than either compound alone. Administration of tamoxifen (500 microg/kg orally) on days 14 and 15 of pregnancy completely abolished the effect of naloxone, indicating a role for estrogens in establishing this inhibitory role of opioids. To examine the participation of the opioid system during lactation, we used groups of rats on days 1, 3, 5, 12 and 19 postpartum either (i) isolated from the pups for 4 h, or (ii) isolated from the pups for 3.5 h and reunited with them and suckled for 30 min. Naloxone, given just before replacing the pups, prevented the increase in serum prolactin levels observed in the suckled group of rats but had no effect on the basal levels of the isolated rats. To examine whether the participation of the opioid system in the release of prolactin is dependent on the variation of progesterone levels, rats on day 20 of pregnancy were implanted with two cannulae containing progesterone (that blocked postpartum ovulation) or cholesterol, and cesarean surgery was performed on day 21. To maintain lactation, pups (1-3 days old) were replaced every 24 h, and 4 days after the cesarean eight pups were placed in the cage at 1800 h to maintain a strong suckling stimulus during the following 24 h. Naloxone administration significantly reduced serum prolactin levels in control (cholesterol) rats but progesterone implants prevented the inhibitory effect of naloxone and this effect was not modified by treatment with estrogen. These results indicate that the opioid system modulates suckling-induced prolactin secretion, passing from an inhibitory action before delivery to a stimulatory action during lactation. This regulatory shift seems to be dependent on the fall in progesterone concentration at the end of pregnancy and the subsequent increase after the postpartum ovulation and luteal phase.     

The effect of maternal prolactin infusion during pregnancy on fetal adipose tissue development

The present study determines whether maternal administration of prolactin (PRL) to dams promotes the abundance of the brown adipose tissue-specific uncoupling protein-1 (UCP1) in fetal and neonatal rat pups. Recombinant PRL (24 micro g/kg per day), or an equivalent volume of saline, were infused into dams (n=19 per group) throughout pregnancy from 12 h after mating. Interscapular brown adipose tissue was sampled either from fetuses at 19.5 days of gestation (term=21.5 days) or from neonatal rat pups at approximately 18 h after birth. The abundance of UCP1 was determined by immunoblotting on adipose tissue samples from individual pups and pooled from groups of pups. This analysis was complemented by immunocytochemistry on representative adipose tissue samples. Maternal PRL infusion resulted in a greater abundance of UCP1 in fetal rats at 19.5 days of gestation (control: 97.2+/-8.4% reference; PRL: 525.6+/-74.4% reference; P<0.001) and in neonates 18 h after birth. In contrast, the abundance of the outer mitochondrial membrane protein voltage-dependent anion channel was unaffected by PRL. Neonatal adipose tissue sampled from pups born to PRL-infused dams possessed fewer lipid droplets, but more UCP1, as determined by immunocytochemistry. Fetal, but not maternal, plasma leptin concentrations were also increased by maternal PRL administration. In conclusion, as rats are altricial, and the potential thermogenic activity of brown adipose tissue develops over the first few days of postnatal life, these changes prior to, and at the time of, birth implicate PRL in fetal and neonatal adipose tissue maturation.     

Acute alcohol consumption disrupts the hormonal milieu of lactating women

Despite the lack of scientific evidence to support the claim that alcohol is a galactagogue, lactating women have been advised to drink alcohol as an aid to lactation for centuries. To test the hypothesis that alcohol consumption affects the hormonal response in lactating women, we conducted a within-subjects design study in which 17 women consumed a 0.4 g/kg dose of alcohol in orange juice during one test session and an equal volume of orange juice during the other. Changes in plasma prolactin, oxytocin, and cortisol levels during and after breast stimulation, lactational performance, and mood states were compared under the two experimental conditions. Oxytocin levels significantly decreased, whereas prolactin levels and measures of sedation, dysphoria, and drunkenness significantly increased, during the immediate hours after alcohol consumption. Changes in oxytocin were related to measures of lactational performance such as milk yield and ejection latencies, whereas changes in prolactin were related to self-reported measures of drunkenness. Although alcohol consumption resulted in significantly higher cortisol when compared with the control condition, cortisol levels were not significantly correlated with any of the indices of lactational performance or self-reported drug effects. Moreover, cortisol levels steadily decreased on the control day, indicating that the procedures were not stressful to the subjects. In conclusion, recommending alcohol as an aid to lactation may be counterproductive. In the short term, mothers may be more relaxed, but the hormonal milieu underlying lactational performance is disrupted, and, in turn, the infant's milk supply is diminished.     

Pancreatic exocrine enzymes during the neonatal period in postmature rats

Pancreatic content of exocrine enzymes in newborn rat pups shows a sharp decline soon after birth. To investigate if this decline is a preprogrammed and, therefore, inherently controlled phenomenon, or a result of external stimulus, prolonged gestation, or postmaturity (2 extra days in utero) in pregnant dams was induced by daily subcutaneous injection of progesterone from the 20th to 22nd days of gestation. Postmature pups showed the same high levels of lipase, trypsin(ogen), and amylase as control pups at birth. They also exhibited the same decline in these enzymes as control pups by the 2nd day after birth, suggesting that it is a response to external stimulus. Pups prevented from suckling retained the high levels of lipase, amylase, and trypsin(ogen) by the 2nd day. The stimulus, therefore, appeared to be the initiation of suckling. Pups prevented from suckling but given 5% glucose water orally every 4 h starting from birth for 24 h showed a sharp decline in amylase with only slight decreases in lipase and trypsin(ogen) by the 2nd day. The components in the feed, therefore, also seem to be an important determinant for selective enzyme release from the pancreas of the neonates. Electron microscopic studies revealed a sharp decrease in the number of zymogen granules in the continuously-suckled pups as compared to age-matched non-suckled counterparts. The reduction in enzyme content thus is the result of secretion in response to suckling.     

Prolactin modulates hypothalamic preproenkephalin,but not proopiomelanocortin,gene expression during lactation

The aim of this study was to examine prolactin (PRL) regulation of preproenkephalin and proopiomelanocortin (POMC) gene expression in the hypothalamus during lactation. In the first experiment, lactating rats were deprived of pups for 3, 6, 12, or 24 h. Preproenkephalin mRNA levels were decreased in the arcuate nucleus (ARC) to 60 or 53% of suckled levels and in the ventromedial nucleus to 70% of suckled levels after 12 or 24 h but were unchanged in the striatum. POMC mRNA levels in the ARC and periarcuate area were increased to 165% of suckled levels within 3 h and remained elevated two- to threefold for 24 h. Subcutaneous administration of bromocriptine to suckled dams markedly suppressed circulating PRL levels and decreased preproenkephalin mRNA signal levels to 38 and 50% of control levels in the arcuate and ventromedial nuclei, respectively. Intravenous administration of oPRL completely reversed this effect. By contrast, bromocriptine with or without administration of ovine PRL (oPRL) did not alter POMC mRNA signal levels in the ARC. Administration of oPRL to pup-deprived dams increased preproenkephalin mRNA levels in the arcuate and ventromedial nuclei and reduced POMC mRNA levels in the ARC to levels similar to suckled control levels. In conclusion, POMC neurons in the ARC appear to be refractory to PRL regulation in the presence of a suckling stimulus, and other components of the suckling stimulus may contribute to the suppression of POMC mRNA levels during lactation. By contrast, PRL provides a regulatory influence for the suckling-induced increase in preproenkephalin mRNA signal levels in arcuate and ventromedial nuclei.     

Effects of maternal iodine deficiency on thyroid hormone economy of lactating dams and pups: maintenance of normal cerebral 3,5,3'-triiodo-L-thyronine concentrations in pups during major phases of brain development

Female rats were fed a diet with a low iodine content (LID), or the same LID supplemented with KI, and mated. Fetuses were obtained at 17 and 21 days of gestation, or pups were killed at different ages after birth. The dams on LID were markedly iodine deficient and developed a large goiter. Their thyroidal iodine content was only 4% of that of LID + I dams. The iodine deficiency of the LID mothers was severe enough to result in very low plasma T4 levels and in hepatic and cerebral T3 deficiency, despite normal circulating levels of T3. The fetuses from LID dams had low concentrations of iodine in their placentas and thyroid glands, and were deficient both in T4 and T3 in all tissues studied, including the brain. After birth, however, suckling LID pups were able to increase the plasma T4 to levels which were higher than those found in either LID fetuses or in adult LID progeny, although plasma T4 was always lower than in age-paired LID + I animals. This increase in T4 was probably due to an approximately 5-fold increase in iodine intake while suckling. Milk from LID mothers was found to contain 22% of the amount of iodine found in milk from LID + I dams, in contrast to their iodine intake, which was about 4% that of the LID + I rats. Cerebral T3 levels were the same for LID and for LID + I pups throughout most of the postnatal period of brain development. This finding might explain the difficulties encountered in obtaining an experimental model of neurological cretinism in rats.     

Abolition of prolactin surge induced by ovarian steroid hormones in the lactating rat.

There are data indicating that stress-induced prolactin (PRL) release is blunted in the lactating rat like the release of other stress-associated hormones. In this experiment, the PRL release evoked by administration of estrogen, which is another principal stimulus for PRL release, was examined in ovariectomized lactating rats 8-15 days after delivery. Estradiol benzoate (EB, 20 micrograms) injections into ovariectomized nonlactating rats induced a PRL surge starting between 13:00 and 15:00 h with a peak at 17:00 h 2 days after the treatment, whereas the EB-induced PRL surge was absent in ovariectomized lactating rats separated from their pups at 09:00 h on the day or in mothers without separation from their pups. Injection of either thyrotropin-releasing hormone (TRH; 10 micrograms/kg) or pimozide (0.5 mg/kg) elevated serum PRL concentrations similarly in lactating and nonlactating rats when examined just before the beginning of the expected estrogen-induced PRL surge. Thus, the main cause for the reduced PRL response to estrogen in lactating rats seems not to be in the pituitary gland but in the brain. Progesterone, which is known to induce a PRL surge in ovariectomized estrogen-primed rats by acting on the mediobasal hypothalamus, also failed to evoke a PRL surge in lactating rats. Recovery from the inhibitory influence of suckling on PRL response to EB followed a time course similar to that observed in response to immobilization stress or to morphine injection; estrogen-induced PRL surge started to recover at 6 days and was almost fully recovered 8 days after weaning.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pancreatic exocrine enzymes during the neonatal period in postmature rats

Summary Pancreatic content of exocrine enzymes in newborn rat pups shows a sharp decline soon after birth. To investigate if this decline is a preprogrammed and, therefore, inherently controlled phenomenon, or a result of external stimulus, prolonged gestation, or postmaturity (2 extra days in utero) in pregnant dams was induced by daily subcutaneous injection of progesterone from the 20th to 22nd days of gestation. Postmature pups showed the same high levels of lipase, trypsin(ogen), and amylase as control pups at birth. They also exhibited the same decline in these enzymes as control pups by the 2nd day after birth, suggesting that it is a response to external stimulus. Pups prevented from suckling retained the high levels of lipase, amylase, and trypsin(ogen) by the 2nd day. The stimulus, therefore, appeared to be the initiation of suckling. Pups prevented from suckling but given 5% glucose water orally every 4 h starting from birth for 24 h showed a sharp decline in amylase with only slight decreases in lipase and trypsin(ogen) by the 2nd day. The components in the feed, therefore, also seem to be an important determinant for selective enzyme release from the pancreas of the neonates. Electron microscopic studies revealed a sharp decrease in the number of zymogen granules in the continuously-suckled pups as compared to age-matched non-suckled counterparts. The reduction in enzyme content thus is the result of secretion in response to suckling. *** DIRECT SUPPORT *** A00DX035 00004     

Effects of an antiserum to rat growth hormone on lactation in the rat

A highly specific antiserum to rat GH (anti-rGH) was used to assess the role of GH in lactation in the rat. When administered alone, anti-rGH had no effect on litter weight gain, whereas bromocriptine reduced serum prolactin concentrations and litter weight gain for up to 7 days when given on day 4 of lactation. When bromocriptine and anti-rGH were given in combination, however, litter weight gain declined even more dramatically so that pups were receiving virtually no milk 2-3 days after treatment. Daily litter exchange failed to prevent this effect. Concurrent injections of highly purified GH (prolactin contamination undetectable) prevented the dramatic decline in litter weight gain induced by combined bromocriptine and anti-rGH treatment, so that these litters grew as well as those receiving bromocriptine alone. Growth hormone did not act by influencing serum prolactin concentrations, which remained low during GH therapy. Direct effects of anti-rGH or GH on the pups (transferred through the milk) were ruled out since virtually identical results were obtained when milk yield was estimated during a 30-min suckling period after a 3-h separation of mother and pups. Lactation had virtually ceased 3 days after treatment with both bromocriptine and anti-rGH, but it could be reinitiated by a single injection of prolactin or GH, and subsequent recovery was virtually complete. The results of this study show that prolactin can maintain a full milk yield in the absence of GH, milk yield is reduced by approximately 50% in the absence of prolactin and milk yield is totally stopped in the absence of prolactin and GH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Development of individual alcohol inhalation chambers for mice: validation in a model of prenatal alcohol

BACKGROUND: The purpose of this work was first to develop a system of individual chambers through which controlled delivery of alcohol vapors allows us to target specific blood alcohol levels (BALs) in mice without requiring the administration of an alcohol dehydrogenase inhibitor. As a proof of concept, we demonstrated that this new system could be used to expose pregnant BALB/c or C57BL/6 mice to alcohol and that the hypothalamic-pituitary-adrenal (HPA) axis of their mature offspring exhibited the well-known hyperactivity that has been previously documented in rats. METHODS: A first series of experiments was designed to establish the parameters that resulted in specific BALs in nonpregnant adult male and female BALB/c as well as C57BL/6 mice that were exposed to various alcohol flow rates. Using information gathered from these experiments, we then chose a regimen of 6 hr of daily vapor exposure in pregnant mice to determine whether this regimen would alter the HPA axis activity of their mature offspring. Control dams were maintained in similar chambers but without alcohol. We first used control mice to assess plasma ACTH levels as a function of shock intensity as well as total duration of the shock session. The most suitable protocol was then used to measure shock-induced ACTH release in 2-month-old male and female offspring that were exposed to alcohol prenatally or not. RESULTS: BALs increased as a function of the alcohol flow rates and remained within an acceptable range of homogeneity, consistency, and reproducibility over the desired periods of time. There were no sex differences in BALs while vapors were delivered. However, there was a strain difference in that BALB/c mice displayed slightly higher BALs than C57BL/6. Female mice also exhibited a slightly more pronounced decrease in BALs, compared with male mice, once removed from the drug. Measurement of plasma ACTH levels as a function of the intensity and duration of the shock sessions indicated that 0.3 mA intensity, 1-sec duration shocks at the rate of 2 shocks/min for 20 min provided the most reliable protocol. We then used the alcohol model in pregnant mice. Alcohol exposure did not interfere with maternal weights during gestation. When offspring were tested at 8 to 9 weeks of age, male and female BALB/c as well as female C57BL/6 mice that were exposed to alcohol vapors prenatally exhibited significantly higher shock-induced plasma ACTH levels, compared with controls of the same strain. CONCLUSIONS: Collectively, our results indicate that the individual alcohol chamber system that we have developed offers a reliable means of exposing mice to alcohol so that they reach predetermined BALs in the absence of the pharmacological manipulations often used to influence alcohol metabolism in this species. This system, which is compatible with normal weight gains, was used to provide evidence that as previously demonstrated in rats, adult murine offspring of alcohol-treated dams exhibit a hyperactive HPA axis. The development of protocols for use in mice offers the possibility of investigating the influence of alcohol in mutant animals with manipulations of specific genes of interest.     

Effects of caffeine on the saturated and monounsaturated Fatty acids of the newborn rat cerebellum

Caffeine (1,3,7-trimethylxanthine) is one of the most commonly consumed drugs in our daily life, and its use is increasing. However, very little attention has been paid to its potential effects on early growth and development. Because of the steady increase in breast feeding of infants and because caffeine diffuses readily into breast milk, the present study examined if caffeine intake by newborn rats during lactation would affect the saturated and monounsaturated fatty acids in the growing cerebellum. A total of 10 timed pregnant rats were purchased from the breeder. At birth litters were combined, and 8 pups were randomly assigned to each dam without regard to the sex of the pups. Dams with litters were divided into 2 groups. Dams of group 1 received a 20% protein diet as a control, and dams of group 2 received a 20% protein diet plus caffeine (4 mg/100 g BW). Pups were killed at day 10. The cerebellums were removed, weighed and homogenized. Gas chromatograph-mass spectrometry was used to identify and quantify free fatty acids. Chronic caffeine exposure from birth to day 10 in pups through the maternal milk resulted in a decrease in cerebellum weight, a significant increase in the saturated fatty acids, and a tendency toward an increase of monounsaturated fatty acids. In addition, there was a slight increase of some of the polyunsaturated fatty acids. However, there was no difference in food intake of the lactating dams and weight gain of the pups between the groups. These data indicate that early caffeine intake by the suckling pups alters the composition of fatty acids of the cerebellum; thus, avoidance of caffeine during lactation is critical. The risks and benefits of caffeine administration in premature infants must be carefully evaluated during this rapid period of brain growth.