Showing papers on "Lactation published in 1989"

Fitness costs of gestation and lactation in wild mammals.

Abstract: Like a number of plants1,2, some mammals commonly produce more progeny than they can afford to rear, terminating investment in some or even all of their offspring once the resources available for breeding are known3–5. Adaptive interpretations of juvenile wastage rely on the argument that the costs of gestation are small compared to those of feeding offspring. Though energetic evidence supports this conclusion6, it is unsafe to assume that the relative costs of gestation and lactation to the mother's survival and future reproductive success follow the same pattern because lactation commonly coincides with the period of maximum food availability. Controlling for individual variation, we show that in wild red deer (Cervus elaphus L) any costs of gestation to the mother's subsequent survival and reproductive success are slight compared to those of lactation.

Release of oxytocin within the supraoptic nucleus during the milk ejection reflex in rats.

Abstract: To investigate the hypothesis that oxytocin may be released within the magnocellular nuclei in vivo, push-pull cannula perfusions were performed in anaesthetized lactating rats in one supraoptic nucleus of the hypothalamus while recording the intramammary pressure and/or the electrical activity of oxytocin cells in the contralateral supraoptic nucleus. Oxytocin content was measured in samples collected over 15 min, under various conditions: 1) with no stimulation; 2) during suckling and suckling-induced reflex milk ejections; 3) during electrical stimulation of the neurohypophysis by trains of pulses that mimicked oxytocin cell bursts; 4) under osmotic stimulation by i.p. injection of 2 ml of 1.5 M NaCl to evoke a tonic and sustained oxytocin release from the neurohypophysis. Oxytocin release within the supraoptic nucleus increased significantly during the milk ejection reflex and, to a lesser extent, during burst-like electrical stimulation of the neurohypophysis. In suckled rats, the increase started before the first reflex milk ejection occurred. There was no apparent correlation between the amount of oxytocin in the perfusates and the number of milk ejections and oxytocin cell bursts occurring during each perfusion period. The amount of oxytocin in the perfusates further increased during facilitation of the milk ejection reflex by intraventricular injections of oxytocin or its analogue, isotocin. When suckling failed to evoke the milk ejection reflex, there was no change in intra-supraoptic oxytocin release. There was also no change after osmotic stimulation. When the push-pull cannula was positioned outside the supraoptic nucleus, there was no increase in the amount of oxytocin during the three types of stimulation tested. These results provide evidence for an endogenous release of oxytocin within the magnocellular nuclei in lactating rats. It is suggested that the increase in such a release induced by suckling is likely to be a pre-requisite for the onset and the maintenance of the characteristic intermittent bursting electrical activity of oxytocin cells leading to milk ejections.

High levels of a parathyroid hormone-like protein in milk.

Abstract: Expression of a parathyroid hormone-like protein (PLP), which is associated with hypercalcemia in malignancy, has recently been localized to normal lactating mammary tissue. We examined the possibility of an extramammary role of PLP by measuring its levels in serum and milk of lactating women. The levels of PLP by radioimmunoassay in serum of lactating and nonlactating women were indistinguishable [4.2 +/- 1.8 and 3.6 +/- 1.0 pg equivalents (eq) of PLP-(1-34) amide per ml, respectively]. As PLP was undetectable in some serum samples, this result does not exclude the possibility that lactation results in a small increase in serum levels of PLP. In contrast, high concentrations of immunoreactive PLP [40,000-75,000 pg eq of PLP-(1-34) amide per ml] and correspondingly high concentrations of bioactive PLP were found in human, rat, and bovine milk. A variety of processed bovine milk products had a PLP content similar to that of fresh bovine milk, whereas infant formulas had lower concentrations, ranging down to undetectable. Although the physiological role of PLP in lactation is unknown, the data establish the presence of PLP in milk and suggest the possibility that PLP may be important in neonatal calcium homeostasis.

Estimation of sow milk nutrient output.

Abstract: Ten replicates of two littermate gilts were used during a 21-d lactation in order to calculate relationships between milk nutrient intake and piglet growth rate and composition of gain. Gilts were fed 14.2 or 10.4 Mcal ME/d and litter size was standardized to 9 or 10 piglets. Piglets had no access to creep feed. Milk production was measured on 10 sucklings over 12 h on d 1, 5, 9, 13, 17 and 21 by the weigh-suckle-weigh method. Heat production of the piglets was measured (RQ method) on the same days in a confinement chamber. Milk composition was determined on the days following milk production measurements. Four to ten piglets/litter were slaughtered at weaning and their body composition was determined. Milk nutrient production during part of lactation was related closely to piglet weight gain and body weight (R2 = .80 to .96). Milk DM, energy and N output over the entire lactation were predicted from piglet ADG (R2 = .87 to .90) when, for each litter, the difference between energy in piglet daily weight gain measured by the slaughter technique and energy in piglet daily weight gain estimated by the RQ method was included in the model. This variable corrects for milk production measurement errors. The relationships were slightly improved, especially for energy output, when the composition of piglet weight gain was taken into account (R2 = .93 to .97).

Lactation inhibits stress-mediated secretion of corticosterone and oxytocin and hypothalamic accumulation of corticotropin-releasing factor and enkephalin messenger ribonucleic acids.

Abstract: The effect of lactation on stress-induced hormone responses and changes in hypothalamic mRNA was assessed in female rats. In control animals the stimulus of ip hypertonic saline resulted in increased plasma levels of corticosterone, oxytocin, and vasopressin and hypothalamic content of CRF and enkephalin mRNA. In lactating females, however, the corticosterone response to this stress failed to reach significance, the plasma oxytocin response was markedly reduced, and the vasopressin response was unaffected. Lactation also resulted in an abolition of the CRF and enkephalin mRNA responses to stress. In contrast, the hypothalamic CRF response to adrenalectomy was unaffected by lactation status. Removal of the pups from their mothers resulted in a return of CRF and enkephalin mRNA responses to stress within 2 days. Lactation is associated with a selective inhibition of normal hypothalamic stress responses.

Effects of maternal diet during late pregnancy and lactation on the development of atopic diseases in infants up to 18 months of age--in-vivo results.

Abstract: One hundred and sixty-two women with respiratory allergy to animal danders and/or pollens were randomly allocated to a diet consisting of either a very low ingestion of hens' egg and cows' milk or a daily ingestion of one hens' egg and about 11 of cows' milk during the last 3 months of pregnancy One hundred and sixty-three infants were followed prospectively up to 18 months of age when the cumulated incidence of atopic disease in each child was evaluated blindly No significant differences in the distribution of atopic disease were found among the infants in relation to the maternal diet during late pregnancy The numbers of skin-prick tests positive to ovalbumin, ovomucoid, beta-lactoglobulin and cows' milk were likewise not influenced by differences in the maternal diet during late pregnancy Genetic factors rather than maternal diet during the perinatal period probably have a greater effect on the incidence of atopic diseases during early infancy

Milk lactose, citrate, and glucose as markers of lactogenesis in normal and diabetic women

Abstract: A study was undertaken to define an appropriate marker of lactogenesis II (the onset of copious milk secretion) in mothers, and to determine the effect of diabetes on this marker. Changes in the concentrations of three milk components--lactose, citrate, and glucose--were measured in 38 normal mothers and 6 type I diabetic mothers up to 10 days after birth. Milk yield was measured in 12 of the normal mothers, and all mothers were asked to note the time of milk "coming in" (the feeling of overfullness of the breasts). The average concentrations of lactose, citrate, and glucose in milk were low for the first 24 h after birth, then between 24 and 48 h after birth there was a rapid increase in the concentrations of lactose and citrate, and this transitional period was followed by a plateau period that began between 60 and 84 h after birth. For individual mothers the transitional period for citrate began 32 +/- 9 h (n = 13) and finished 77 +/- 10 h (n = 17) after birth, and for lactose the transitional period finished at 53 +/- 12 h (n = 29) after birth. For diabetic mothers these times were significantly later. The average 24-h milk intake by infants increased from 82 to 556 ml/24 h between 24 and 144 h after birth. Milk intakes were correlated with the concentration of lactose (r = 0.52, n = 51, p less than 0.001), citrate (r = 0.47, n = 47, p less than 0.001), and glucose (r = 0.69, n = 50, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

The mRNA encoding a parathyroid hormone-like peptide is produced in mammary tissue in response to elevations in serum prolactin.

Abstract: During lactation, a dramatic rise in serum PRL stimulates milk production, resulting in a substantial rise in calcium mobilization from gut and bone. We found that the production of a newly characterized calcium-mobilizing PTH-like peptide (PTH-LP) by mammary tissue was tightly linked to lactation, suggesting a possible role for PRL in the expression of PTHLP. Here it is shown that suckling results in both an elevation in serum PRL and the appearance of PTHLP mRNA in mammary tissue. Bromocriptine, a potent inhibitor of PRL secretion, blocked the sucklingassociated rise in serum PRL and the subsequent induction of PTH-LP mRNA in mammary gland. Furthermore, injection of PRL dramatically induced PTHLP mRNA in unsuckled puerperal glands, but not in glands on day 21 of pregnancy. Thus, the correlation between serum levels of PRL and the expression of PTH-LP mRNA in mammary tissue extends the role of PRL in milk production and suggests a possible mechanism for the PRL effects on calcium metabolism.

Reproductive performance, body weight and body condition of breeding sows with differing body fatness at parturition, differing nutrition during lactation, and differing litter size

Abstract: One hundred and two Large White × Landrace Fl hybrid sows were allocated over four parities in a factorial design to two levels of target P2 backfat thickness at parturition (20 mm, F v. 12 mm, T), two levels of lactation feeding {ad libitum, H v. 3 kg/day, L), and two sizes of sucking litter (six v. 10). Sows attained 13 mm P2 when first mated at 126 kg live weight. Fatness (P2, mm) at weaning was significantly influenced by target fatness at parturition (14·2 v. 9·3), lactation feeding level (13·7 v. 10·0), and litter size (12·7 v. 11·0). Changes in backfat (P2, mm) during 28-day lactation were significantly influenced by target fatness at parturition (—5·0 v. —2·5), lactation feeding (-2 0 v. —5·4), and litter size (—2·9 v. -4·6). Sow live weight (kg) at weaning was significantly influenced by target fatness at parturition (211 v. 192), lactation feeding (218 v. 186), and litter size (208 v. 196). Changes in live weight (kg) during 28-day lactation were significantly influenced by target fatness at parturition (—26 v. — 12), lactation feeding (—5 v. —31), and litter size (—12 v. —25). With multiparous sows only, total food intake during 28-day lactation was negatively related to total food intake in pregnancy. Change in backfat (P2, mm) during 28-day lactation = -0·28 - 0·27 P2 at parturition + 0·04 lactation food intake — 0·50 litter size. Change in live weight (kg) during 28-day lactation = -3·8 — 0·15 live weight post partum + 0·36 lactation food intake — 3·3 litter size. Sows with target fat levels of 20 mm P2 at parturition had better food conversion efficiencies than sows with target fat levels of 12 mm. Target fatness at parturition, and especially lactation food intake, but not litter size, significantly influenced the interval (days) from weaning to oestrus in parity 1 (9·1 v. 14·2 and 7·8 v. 15·3, but 11·6 v. 11·5), while n i subsequent parities only litter size influenced the interval (days) from weaning to oestrus (6·0 v. 8·0). Birth weight (kg) of piglets was influenced only marginally by target fatness at parturition (1·4 v. 1·2) in parity 1, and not by the other factors, or in subsequent parities. Piglet growth rate was affected by both target fatness at parturition and litter size, but by lactation feeding level only in the last week of lactation. The relationship between fatness at weaning (mm) and the weaning to oestrus interval (days) for primiparous sows can be expressed as 26·6 — 1·28 P2. High level feeding in lactation imparted production and efficiency benefit in both primiparous and multiparous sows, while pregnancy feeding to a target of 20 mm rather than 12 mm at parturition was of benefit for primiparous sows.

Lactotransferrin gene expression in the mouse uterus and mammary gland.

Abstract: The mouse mammary gland and uterus expressed the gene for the secretory protein lactotransferrin under various physiological conditions. Lactotransferrin, however, was induced by estrogen in a time- and dose-dependent fashion in the uterus of the immature mouse, but was not affected by estrogen in the mammary gland. Differences were also found in the expression of lactotransferrin in mammary glands and uteri of adult females during lactation. A high level of the protein was detected by immunocytochemistry in uterine epithelial cells 1 day after parturition, but immunoreactivity disappeared quickly thereafter. Lactotransferrin message was, however, relatively abundant in the mammary gland at the end of the lactation period. The presence of lactotransferrin in various tissues also was investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis. Two forms of immunoreactive material was detected by this method; a 70K band was found in uterine luminal fluid from the estr...

Increasing Breast Milk Production for Premature Infants With a Relaxation/Imagery Audiotape

Abstract: Many women whose premature infants are hospitalized in a newborn intensive care unit choose to express breast milk for their babies. Yet anxiety, fatigue, and emotional stress are powerful inhibitors of lactation. To facilitate the breast-feeding experience, intervention mothers were given a 20-minute audio cassette tape based on relaxation and visual imagery techniques. At a single follow-up expression of milk at the hospital approximately 1 week after enrollment, they expressed 63% more breast milk than a randomized group of control mothers. The fat content of the breast milk in the two groups was not significantly different. Among a small group of mothers whose infants were receiving mechanical ventilation, the increase in milk volume compared with that of control mothers was 121%. Longer-term effects of the relaxation/imagery approach (such as extending the duration of breast-feeding or reducing parental stress after hospital discharge) and the physiologic basis for the increased volume of expressed milk (improved milk production v more efficient milk ejection) are appropriate topics for future research.

Hormonal regulation of milk protein gene expression.

Abstract: Throughout the life of the mammal development of the mammary gland is dependent on the interaction of multiple hormones and growth factors with several different cell types. During lactation these hormones and growth factors interact with the epithelial cells of the mammary gland to produce milk with a very high, and unique, protein content. This chapter focuses on hormones that regulate milk protein gene expression during lactation.

The effects of dietary fat or fiber addition on yield and composition of milk from sows housed in a warm or hot environment.

Abstract: Sixty sows were individually penned in a thermoneutral (20 degrees C) or hyperthermal (32 degrees C) environment and fed a basal (corn-soybean meal), high-fiber (48.5% wheat bran) or high-fat (10.6% choice white grease) diet from d 100 of gestation through a 22-d lactation. The diets were determined to contain 3.28, 2.76 and 3.75 Mcal ME/kg, respectively. All pigs received 8.0 Mcal of ME and 17.5 g of lysine daily prior to parturition and were allowed to consume their respective diets ad libitum after parturition. Litter size was standardized at 9 to 10 pigs by d 2 postpartum. Milk yields were determined for five, 4-d periods from about d 2 through 22 of lactation via a D2O dilution technique. Daily milk yield and litter weight gain began to plateau, and the efficiency of utilizing milk DM and milk energy for gain was depressed (P less than .01), in the latter stages of the lactation. Heat exposure (32 degrees C) reduced (P less than .05) voluntary ME intake and milk energy yield of the sow and increased (P less than .05) the sow's weight loss during lactation. In the hot environment, increasing dietary energy concentration resulted in a linear (P less than .08) increase in milk fat content and milk energy yield over the duration of the 22-d lactation. In the latter stages of lactation, pigs consuming high-fat milk required more (P less than .09) milk and milk energy per unit of weight gain. In the warm environment, milk energy yield was increased by dietary fat or fiber additions in early lactation, but not in late lactation. These results indicate that the effects of thermal heat stress on sow milk energy yield and litter weight gain are aggravated by dietary fiber addition and minimized by dietary fat addition.

Maternal transfer of photoperiodic information in Siberian hamsters. II. The nature of the maternal signal, time of signal transfer, and the effect of the maternal signal on peripubertal reproductive development in the absence of photoperiodic input.

Abstract: Peripubertal reproductive development of Siberian hamsters is controlled by maternally derived photoperiodic information and the ambient photoperiod present after weaning. Previous experiments suggested that the maternally derived information is transferred during gestation, not during lactation. Development was examined in several photo periods following manipulation of gestational and lactational photoperiods; development was influenced by the gestational, but not lactational, photoperiod. Second, effects of the gestational photoperiod were observed in young reared in constant light (LL) from Day 15. Depriving the young of ambient photoperiodic information after Day 15 allows a mire direct assessnient of the sighal riceivi’d from their dams, Finally, melatonin injections to long-day dams, at certain times of day, caused transmission of a short .day signal to young, as evidenced by their development in LL and light-dark cycles. Thus, a maternally derived signal that is dr’pends’nt on melatonin influences reproductive development of the young during gestatio#; the maternally directed pattern of development can subsequently be modified by the you gigs’

Insulin sensitivity and responsiveness during lactation and dry period in goats

Abstract: To investigate the role of insulin in partitioning nutrients between the mammary gland and other tissues during lactation in ruminants, euglycemic-hyperinsulinemic clamps were performed in goats during early lactation (15-26 days postpartum), midlactation (78-91 days postpartum), and dry period (169-194 days postpartum). Insulin was infused at 0.4, 0.7, 1.9, 4.4, and 10 micrograms/min. Basal plasma glucose was constant during all periods despite the fact that basal glucose utilization was approximately 3 times higher during lactation than dry period. Basal plasma insulin was similar during early lactation and dry period but increased during midlactation. Insulin infusion resulted in a dose-dependent stimulation of glucose utilization. The insulin-stimulated glucose utilization above basal was greatly impaired during early lactation when compared with dry period, but this only occurred at very high plasma insulin. Insulin infusion also resulted in a decrease in glucose production; the maximal insulin effect is achieved at the lowest insulin infusion rate. The ability of insulin to decrease glucose production was significantly improved during early lactation when compared with dry period. This phenomenon may provide a mechanism to save gluconeogenic substrates during early lactation. In contrast, midlactation did not result in any significant change in insulin action with both glucose utilization and glucose production.

Human Lactation II: Endogenous Fatty Acid Synthesis by the Mammary Gland

Abstract: We studied the effects of a diet that was low in fat, high in carbohydrate (CHO) on milk lipid composition and de novo endogenous fatty acid synthesis by the mammary gland in five lactating women. The women consumed either a low fat (LF) (5% fat, 80% CHO) diet or a high fat (HF) (40% fat, 45% CHO) diet. Fat synthesis was determined after an oral dose of 500 mg/kg D2O by measuring the incorporation of deuterium into C10:0 to C18:0 saturated fatty acids of milk fat and plasma triglycerides by gas chromatography-mass spectrometry. Synthesis of plasma C16:0 and C18:0 triglycerides was barely detectable while women consumed the HF diet, but was increased 6-fold during the LF diet. Medium chain fatty acids secreted by the mammary gland increased from 12.8% (HF diet) to 16.3% (LF diet) in milk fat from four of five subjects (p=0.027). Medium chain fatty acid secretion, however, increased from 13.9% (HF diet) to 29.9% (LF diet) in one subject. The primary fatty acids synthesized during lactation were C10:0, C12:0, and C14:0 in the majority of women studied. The LF diet significantly increased the apparent synthesis of C14:0 (p=0.05), whereas no changes were observed in C12:0, C16:0, or C18:0. One subject had highly enriched C16:0 and C18:0 fatty acids in her milk on the LF diet, which could have been the result of mammary synthesis or of transport and secretion of hepatically synthesized lipids.

Detection of Salmonella dublin mammary gland infection in carrier cows, using an enzyme-linked immunosorbent assay for antibody in milk or serum.

Abstract: An ELISA has been developed for measurement of milk and serum IgG concentrations directed against Salmonella dublin. Four groups of cows were studied: group A--7 experimentally challenge-exposed cows (infected, recovered group); group B--6 normal uninfected randomly selected control cows; group C--7 naturally occurring S dublin carrier cows; and group D--6 normal uninfected S dublin negative cows from the same herd as group C. Group-A cows were inoculated orally, or inoculated orally and then IV, but none became a S dublin carrier. As expected, all 7 group-A cows responded with a marked increase in ELISA titer after oral exposure to virulent S dublin, starting with a mean serum titer of 17.7% and reaching a peak mean serum titer of 79.3% approximately 76 days after initial exposure. As determined by necropsy and organ culturing of the remaining cows, none of the group-A cows became carriers. The mean serum ELISA titer for group-B uninfected control cows was 14.1% (SD +/- 12.8%). The mean milk ELISA titer was -1.0% (SD +/- 5.5%). Colostrum and then milk gave false-positive results for up to 2 weeks after onset of lactation. Group-B cows were culture negative for S dublin in feces and milk during lactation, and when tissues were cultured after euthanasia. Milk and serum samples for ELISA, and milk and fecal samples for culturing were taken from all group-A and -B cows twice a week for 6 months. Statistical correlation (P less than 0.05) was found between serum and milk ELISA titers.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced responses of prolactin and catecholamine to stress in the lactating rat.

Abstract: Prolactin, GH, TSH, adrenaline and noradrenaline responses to the stress of immobilization were compared between lactating and non-lactating dioestrous rats. The concentrations of GH in plasma were reduced to a similar degree by the immobilization of lactating and non-lactating rats, and TSH levels were unchanged in both groups. The increases in plasma concentrations of adrenaline and noradrenaline induced by stress were significantly smaller in lactating than in non-lactating rats. Immobilization caused a marked increase in prolactin levels in the plasma of non-lactating rats but no increase in lactating rats. These changes may help to save energy and maintain milk production during the period of lactation.

Changes in immunostaining for oxytocin in the forebrain of the female rat during late pregnancy, parturition and early lactation.

Abstract: Serial brain sections of female rats at late pregnancy, parturition or early lactation were immunostained for oxytocin. Immunoreactive perikarya were visible in the magnocellular nuclei in all experimental animals as well as in ovariectomized, nulliparous controls. During late pregnancy and at parturition additional immunostaining appeared in groups of perivascular neurons in the preoptic region, the lateral subcommissural nucleus, the perifornical region and scattered throughout the ventral portion of the hypothalamus. Immunostaining of almost all of these perivascular neurons disappeared by day two postpartum, while another population of oxytocin neurons, without association with blood vessels, appeared in these brain regions after parturition. Immunostaining of processes from oxytocinergic neurons in the periventricular nucleus increased markedly near parturition. Many of these processes projected toward the third ventricle. Oxytocinergic neuronal systems that are activated in late pregnancy and early postpartum may contribute to several physiological changes associated with parturition and lactation including the onset of maternal behavior.