Bioactivity of prolactin isoforms: lactation and recovery of menses in nursing women.
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To assess whether plasma prolactin (PRL) characteristics relate to lactogenesis and absence or presence of menstrual cycles, we measured bioactive PRL (BIO-PRL) using the Nb2 assay, immunoreactive PRL (IR-PRL) by radio-immunoassay, calculated equations describing the BIO-PRL-IR-PRL relationship and separated charged PRL isoforms (by chromatofocusing) in five amenorrhoeic and five cycling nursing women at 6 months postpartum and in 10 cycling non-nursing women. Plasma samples were drawn before and 30 min after a suckling episode at 0800, 1600 and 2400 h in nursing women and at the same hours in non-nursing women. BIO-PRL and IR-PRL concentrations were highest in amenorrhoeic nursing women, intermediate in cycling nursing women and lowest in cycling non-nursing women. The BIO-PRL-IR-PRL relationship shows that a given amount of IR-PRL corresponds to equivalent amounts of BIO-PRL in cycling nursing and cycling non-nursing women, and to a larger extent in amenorrhoeic nursing women. IR-PRL was present in plasma as several charge isoforms. Bioactive isoforms eluting at pH 6.0-5.1 were found in amenorrhoeic and cycling nursing women, reaching similar concentrations after suckling. Bioactive isoforms eluting at pH 7.0-6.1 were found only in amenorrhoeic nursing women. We speculate that isoforms eluting at pH 6.0-5.1 may play a role in lactation and isoforms eluting at pH 7.0-6.1, in lactational amenorrhoea. (+info)
Elevated expression of liver gamma-cystathionase is required for the maintenance of lactation in rats.
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Liver gamma-cystathionase activity increases in rats during lactation; its inhibition due to propargylglycine is followed by a significant decrease in lactation. This is reversible by N-acetylcysteine administration. To study the role of liver gamma-cystathionase and the intertissue flux of glutathione during lactation, we used lactating and virgin rats fed liquid diets. Virgin rats were divided into two groups as follows: one group was fed daily a diet containing the same amount of protein that was consumed the previous day by lactating rats (high protein diet-fed rats); the other virgin group was fed the normal liquid diet (control). The expression and activity of liver gamma-cystathionase were significantly greater in lactating rats and in high protein diet-fed virgin rats compared with control rats. The total glutathione [reduced glutathione (GSH) + oxidized glutathione (GSSG)] released per gram of liver did not differ in lactating rats or in high protein diet-fed rats, but it was significantly higher in these two groups than in control virgin rats. Liver size and the GSH + GSSG released by total liver were significantly higher in lactating rats than in high protein diet-fed virgin rats, and this difference was similar to the amount of glutathione taken up by the mammary gland (454.2 +/- 36.0 nmol/min). The uptake of total glutathione by the lactating mammary gland was much higher than the uptakes of free L-cysteine and L-cystine, which were negligible. These data suggest that the intertissue flux of glutathione is an important mechanism of L-cysteine delivery to the lactating mammary gland, which lacks gamma-cystathionase activity. This emphasizes the physiologic importance of the increased expression and activity of liver gamma-cystathionase during lactation. (+info)
Protective effects of pregnancy and lactation against N-methyl-N-nitrosourea-induced mammary carcinomas in female Lewis rats.
(27/4708)
The role of parity before and after N-methyl-N-nitrosourea (MNU) treatment in protection against mammary carcinogenesis was investigated. The effect of lactation on reduction in the incidence of mammary carcinoma was also examined. Parous rats were compared with respective age-matched virgins (AMVs). Pregnancy and lactation prior to MNU exposure significantly reduced both the incidence of mammary carcinoma (22 versus 72%) and the average number of mammary carcinomas per rat (0.22 versus 0.86) and significantly prolonged the latency of the carcinomas (247 versus 215 days). Pregnancy and lactation following MNU exposure also significantly reduced both the incidence of mammary carcinoma (25 versus 94%) and the average number of mammary carcinomas per rat (0.25 versus 1.50) and significantly prolonged the latency (240 versus 155 days). Lactation showed an additive effect on the reduction in mammary cancer. Pregnancy suppressed the number of estrogen receptor (ER)- and progesterone receptor (PgR)-positive cells and lowered the cell proliferation rate in the non-tumoral mammary glands. Since the majority (>76%) of the mammary carcinomas was hormone dependent in both the parous and AMV rats, pregnancy and lactation appear to decrease the ER- and/or PgR-positive cells presumed to be the progenitors of hormone-dependent carcinomas and they lowered the cell turnover necessary for tumor promotion in parous rats, resulting in a lower mammary carcinoma yield. (+info)
Breast growth and the urinary excretion of lactose during human pregnancy and early lactation: endocrine relationships.
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Breast volume and morphology of eight subjects were measured before conception and at intervals throughout pregnancy until 1 month of lactation. Breast volume before conception ranged from 293 to 964 ml. At the end of pregnancy the volume of breast tissue had increased by 145+/-19 ml (mean+/-S.E.M., n = 13 breasts, range 12-227 ml) with a further increase to 211+/-16 ml (n = 12 breasts, range 129-320 ml) by 1 month of lactation. Urinary excretion of lactose increased at 22 weeks of pregnancy, signalling the capacity of the breast to synthesize lactose at this time. During pregnancy, both the change in breast volume and the change in cross-sectional area of the areola were related to the concentration of human placental lactogen in the plasma. The growth of the nipple and the rate of excretion of lactose were related to the concentration of prolactin in the plasma. During the first 3 days after birth, the rate of excretion of lactose was related to the rate of excretion of progesterone. There was no relationship between the growth of the breast during pregnancy and the amount of milk produced at 1 month of lactation. (+info)
Breast volume and milk production during extended lactation in women.
(29/4708)
Quantitative measurements were made of relative breast volume and milk production from 1 month of lactation until 3 months after weaning, and the storage capacity of the breasts was calculated. The increase in breast tissue volume from before conception until 1 month of lactation was maintained for the first 6 months of lactation (means+/-S.E.M.) (190.3+/-13.1 ml, number of breasts, nb = 46). During this period of exclusive breast-feeding, 24 h milk production from each breast remained relatively constant (453.6+/-201 g, nb = 48), and storage capacity was 209.9+/-11.0 ml (nb = 46). After 6 months, breast volume, milk production and storage capacity all decreased. There was a relationship between 24 h milk production and the storage capacity of the breasts, and these both appeared to be responding to infant demand for milk. At 15 months of lactation, the 24 h milk production of each breast was substantial (208.0+/-56.7 g, nb = 6), even though the breasts had returned to preconception size. This was associated with an apparent increased efficiency of the breast (milk production per unit breast tissue) after 6 months, which may have been due to redistribution of tissues within the breast. The possible causes of the decrease in breast volume are discussed. (+info)
Reproductive, metabolic, and endocrine responses to feed restriction and GnRH treatment in primiparous, lactating sows.
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The current experiment was carried out to determine whether exogenous GnRH treatment in primiparous, lactating sows undergoing feed restriction would improve reproductive performance after weaning. Sows were allocated to one of three treatments: AA sows (n = 8) were fed to appetite throughout a 28-d lactation, AR (n = 12) and AR + GnRH (n = 12) sows were fed as AA sows from farrowing to d 21 of lactation, and feed intake was reduced to 50% of the ad libitum intakes from d 22 to 28. The AR + GnRH sows received 800 ng of GnRH i.v. every 6 h from d 22 to 28 of lactation, and AA and AR sows received saline. Sow weight, backfat, and litter weight were recorded weekly. Within 2 d after farrowing, litter size was standardized to 8 to 10. At d 17 of lactation, an indwelling jugular catheter was surgically implanted in each sow. Blood samples were taken for characterization of plasma LH, FSH, insulin, IGF-I, and leptin by RIA at d 21 and before and after weaning on d 28 of lactation. After weaning, all sows were given ad libitum access to feed, checked for onset of standing estrus twice daily with mature vasectomized boars, and inseminated 12 and 24 h after onset of standing estrus with pooled semen from the same fertile boars (3 x 10(9) sperm/AI). After breeding, feed allowance was reduced to NRC (1988) requirements for gestation. At d 28 +/- 3 of gestation, sows were killed and ovulation rate and embryo survival were determined. Restricted sows lost more weight during lactation than AA sows (P < .02). During the period of feed restriction, plasma IGF-I and postprandial insulin and leptin in AR and AR + GnRH sows, and LH pulse frequency in AR sows, were lower than those in AA sows (P < .04). Associations (P < .004) between plasma insulin and leptin and between leptin and mean LH concentrations were established. The LH pulse frequency in AR + GnRH sows did not differ from that in AA sows before weaning. After weaning, maximum, mean, and minimum LH concentrations in the AA and AR sows, and FSH concentrations in AR sows, increased (P < .05) in response to weaning. Paradoxically, GnRH treatment in lactation seemed to suppress the expected LH and FSH responses to weaning. Ovulation rate and embryo survival were not different among the three groups. In conclusion, although exogenous GnRH therapy restored LH secretion in feed-restricted sows, it did not improve overall reproductive performance. (+info)
Two stages of increased IgA transfer during lactation in the marsupial, trichosurus vulpecula (Brushtail possum).
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The polymeric Ig receptor (pIgR) and J chain molecules are involved in the transfer of IgA across the mammary gland epithelia into milk. The J chain binds two IgA molecules to form dimeric IgA, and the pIgR transports this complex through epithelial cells. We report here the cloning of the first marsupial homologues for the pIgR and J chain from the brushtail possum. Marsupial young are born after a short gestation and are less developed than eutherian newborn. The pouch young is completely dependent on milk as its sole source of nutrition during early lactation and this phase can be considered to be equivalent to an external gestation. Two periods of increased expression of pIgR, J chain, and IgA heavy chain mRNAs were observed in the mammary gland during lactation. The first occurs for a brief period after birth of the pouch young and is likely to reflect IgA transfer via the colostrum. The second period of increased expression, which is unique to marsupials, occurs after the early lactation period and just before young exit the pouch. We propose that this represents a second colostral-like phase at the end of the external gestation. (+info)
Randomized trial of the short-term effects of dieting compared with dieting plus aerobic exercise on lactation performance.
(32/4708)
BACKGROUND: Limiting postpartum weight retention is important for preventing adult obesity, but the effect of weight loss on lactation has not been studied adequately. OBJECTIVE: We evaluated whether weight loss by dieting, with or without aerobic exercise, adversely affects lactation performance. DESIGN: At 12+/-4 wk postpartum, exclusively breast-feeding women were randomly assigned for 11 d to a diet group (35% energy deficit; n = 22), a diet plus exercise group (35% net energy deficit; n = 22), or a control group (n = 23). Milk volume, composition, and energy output; maternal weight, body composition, and plasma prolactin concentration; and infant weight were measured before and after the intervention. RESULTS: Weight loss averaged 1.9, 1.6, and 0.2 kg in the diet, diet + exercise, and control groups, respectively (P < 0.0001) and was composed of 67% fat in the diet group and nearly 100% fat in the diet + exercise group. Change in milk volume, composition, and energy output and infant weight did not differ significantly among groups. However, there was a significant interaction between group and baseline percentage body fat: in the diet group only, milk energy output increased in fatter women and decreased in leaner women. The plasma prolactin concentration was higher in the diet and diet + exercise groups than in the control group. CONCLUSIONS: Short-term weight loss (approximately 1 kg/wk) through a combination of dieting and aerobic exercise appears safe for breast-feeding mothers and is preferable to weight loss achieved primarily by dieting because the latter reduces maternal lean body mass. Longer-term studies are needed to confirm these findings. (+info)