Showing papers on "Lactation published in 1992"

Carry-over of aflatoxin from cows' food to milk

Abstract: Two experiments were made. In experiment 1, dairy cows in early lactation (2 to 4 weeks) and dairy cows in late lactation (34 to 36 weeks) were given aflatoxin B, (AFBt)at a level of 34 to 39 fig/day by feeding them contaminated compound food. The aflatoxin Mrcontent(AFMj) of raw milk was determined four times during the experimental period of 14 days. The milk yield was measured daily.The carry-over rate of aflatoxin was proportionately 0·062 and 0·018 for cows in early and late lactation respectively. This difference was not only due to milk production level but possibly also associated to AFB, liver metabolism.In experiment 2, eight high (40 kg milk per day) and eight low (16 kg milk per day) milk yielding cows, carry-over of AFB1 from compound food into AFM, in milk was measured at different levels ofAFB7 intake ranging from 7 to 57 fig/day. Independent of AFBj-intake, high-producing dairy cows had a higher carry-over rate than low producing animals (proportionately 0·038 v. 0·025). Carry-over ofAFB1 to AFM, was linearly correlated with milk yield. Variations in the level of AFM1 in milk of individual cows were not due to variations in milk yield. The relationship between AFB2 intake per day and AFM^content in milk per kg could be described by the formula: AFMj (ng/kg milk) = 119 AFB, intake (fig per cow per day) + 1·9. This means that in order to produce milk with less than 0·05 fig AFM, per kg milk the average daily individual intake in a herd should be limited to 40 fig AFB7 per day.As dairy cows in their early to mid lactation period consume large quantities of compound food, a maximum level of AFB3 in dairy foods has to be set at an acceptable daily intake (ADI) value to guarantee that AFM1 levels in milk do not exceed tolerable levels.

Maternal avoidance of eggs, cow's milk, and fish during lactation: effect on allergic manifestations, skin-prick tests, and specific IgE antibodies in children at age 4 years.

Abstract: Two matched groups of children with a family history of atopy/allergy were observed from birth In one group (n = 65) the mothers had a diet free from eggs, cow9s milk, and fish during the first 3 months of lactation, whereas the mothers in the other group (n = 50) had a normal diet Atopic/allergic manifestations, skin-prick tests, and specific IgE antibodies to egg white and cow9s milk during the first 18 months of life have been reported previously At 4 years of age the children underwent a clinical examination, skin-prick tests, and determination of specific IgE antibodies in serum against certain food and inhalant allergens Both the cumulative incidence and the current prevalence of atopic dermatitis were significantly lower in the group of children whose mothers had adhered to a hypoallergenic diet during lactation, whereas all other atopic manifestations were similar The number of children with positive skin-prick tests and specific IgE antibodies did not differ significantly, but the number of positive skin-prick tests and specific IgE antibody reactions in serum was significantly lower in the children of mothers adhering to the diet, indicating a milder degree of sensitization in these children

Suckling is a persistent stimulus to the adrenocortical system of the rat.

Abstract: The present experiments investigated the hypothesis that lactation constitutes a chronic stress to the adrenocortical system. To determine whether the normal circadian control of the adrenocortical system or the ability to mount an adequate ACTH response to stress are modified during lactation, we compared morning and evening basal and stress-induced ACTH, corticosterone (B), and PRL secretion as well as pituitary ACTH content and thymus weight in virgins and lactating females on day 10 of lactation. We also compared the capacity of B to suppress ACTH secretion in adrenalectomized virgin or lactating females, both given various B pellet replacement doses (40-130% B) for 5 days. In addition, we investigated the influence of decreased litter size and increased caloric intake on basal circadian activity in the adrenocortical system. Finally, we measured suckling-induced activation of ACTH and B release and restoration of basal morning ACTH and B levels after pup separation. In all 10-d lactating females, bas...

Re-evaluation of the whey protein/casein ratio of human milk.

Abstract: Total casein subunits as well as whey proteins were quantitated in human milk samples during lactation. Two independent methods were used: precipitation at pH 4.3 in the presence of Ca2+ followed by Kjeldahl analysis and polyacrylamide gradient gel electrophoresis (PAGGE) followed by densitometric scanning. Both methods yielded similar results: casein synthesis is low or absent in early lactation, then increases rapidly and subsequently decreases. The concentration of whey proteins decreases from early lactation and continues to fall. These changes result in a whey protein/casein ratio of about 90:10 in early lactation, 60:40 in mature milk and 50:50 in late lactation. These observations indicate that the synthesis and/or secretion of caseins and whey proteins is regulated by different mechanisms. In addition, the relative proportion of the different beta- and kappa-casein subunits was found to vary throughout lactation.

Milk production by mothers of premature infants: influence of cigarette smoking.

Abstract: The volume of milk produced by mothers who smoked cigarettes (n = 11) and control subjects who did not smoke (n = 29) was compared after the delivery of their preterm infants (28 to 32 weeks gestation). Milk production was significantly less among those who smoked, with or without adjusting for age, race, parity, gravidity, weight-for-height, prior nursing experience, customary alcohol and caffeine intake, infant birth weight, and pumping frequency. Each mother maintained her milk production using an electrical breast pump and without the stimulus of her infant suckling at the breast. Daily frequency and duration of breast pump usage were similar in the two groups. At 2 weeks postpartum, 24-hour milk volumes were 406 +/- 262 mL for mothers who smoked and 514 +/- 338 mL for control subjects. Between 2 to 4 weeks postpartum, the mean change in 24-hour milk volume (milliliters per 24 hours) of control subjects increased (+113 +/- 179 mL, P < .005), whereas milk volume of mothers who smoked cigarettes remained unchanged (-47 +/- 122 mL, P = .25). The percentage change in milk volume between 2 and 4 weeks for the combined groups was significantly related to four factors: pumping frequency, change in daily pumping frequency, day of initiation of pumping, and smoking status. Total and protein nitrogen, lactose, calcium, and phosphorous concentrations did not differ in milks from mothers who smoked cigarettes and mothers who did not smoke.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of fish oil on the fatty acid composition of human milk and maternal and infant erythrocytes.

Abstract: To examine the effect of fish oil supplementation on the fatty acid (FA) composition of human milk and maternal and infant erythrocytes, five lactating women were supplemented with 6 g of fish oil daily for 21d. Usual maternal diets contained 1,147 mg of total n−3 FA, with 120 mg from very long-chain (>C18) n−3 FA. Supplementation increased dietary levels to 3,092 mg of total n−3 FA and 2,006 mg of very long-chain n−3 FA. Milk samples were collected daily, prior to fish oil ingestion, and at 4-h intervals on days 1, 7, 14 and 21. Milk n−3 FA content increased within 8 h and reached steady state levels within one week. The n−6 fatty acid content decreased. Erythrocyte eicosapentaenoic acid content increased from 0.24% to 1.4% (P<0.01) in mothers and from 0.11% to 0.70% (P<0.05) in infants. Docosapentaenoic acid increased from 1.4% to 2.2% (P<0.05) in mothers and from 0.30% to 0.78% (P<0.01) in infants. There was no significant change in docosahexaenoic acid or n−6 fatty acid content. Maternal platelet aggregation responses were variable. No differences in milk or plasma tocopherol levels were noted.

Polyamine concentration in rat milk and food, human milk, and infant formulas.

Abstract: The polyamine concentration in rat milk and food, human milk, and infant formulas was estimated by HPLC. In rat milk, the concentration of putrescine and spermine was low (generally under 2.5 nmol.mL-1 for putrescine and under 1 nmol.mL-1 for spermine). The spermidine concentration was higher and seemed to increase during lactation. The rat food was richer in polyamines than the rat milk (about 150 times for putrescine and spermine, about 30 times for spermidine). We already proved that ingestion of spermine or spermidine can induce precocious maturation of the rat intestine. The present observations suggest that polyamines contained in rat food could play an important role in postnatal maturation of the rat intestine. The polyamine concentration of human milk was measured from 60 different mothers during a period extending from the 1st wk to the 6th mo of lactation. Great variation was observed. During the 1st mo of lactation, the general pattern was as follows: putrescine concentration generally varied little (from 1 to 3 nmol.mL-1), spermine and spermidine concentrations showed a similar pattern (the highest values appeared at the end of the 1st wk of suckling). After the 4th mo of lactation, putrescine concentration increased slightly, whereas spermine and spermidine concentration stayed almost stable. The concentrations of polyamines in 18 powdered milks for babies were estimated. Spermine and spermidine contents were lower than those in human milk. A protective effect of spermine or spermidine against alimentary allergies is suggested.

Tumor Necrosis Factor-α in Human Milk

Abstract: We previously demonstrated that certain biologic activities in human milk were partially blocked by antibodies directed against human tumor necrosis factor-α (TNF-α). In this study, immunochemical methods were used to verify the presence of TNF-α in human milk obtained during the first few days of lactation. Gel filtration revealed the presence of TNF-α by RIA in molecular weight fractions between 80 and 195 kD. TNF-α could not be detected consistently by conventional Western blotting or cytotoxic assays. Although immunoreactive bands were detected by a Western blot-125I protein A technique in TNF-α-positive fractions from gel filtration, those bands proved to be nonspecific. TNF-α in milk was reliably quantified by the competitive RIA. Those studies revealed that the concentrations of TNF-α in milk were 620 ± 183 pg/mL. Although RNA to TNF-α was detected in milk leukocytes by Northern blotting, little TNF-α was found in those cells before or after stimulation with N-formyl-l-methionyl-l-leucyl-l-phenylalanine or 4β-phorbol-12β-myristate-13α-acetate. The origin of this cytokine in human milk remains unclear. Nevertheless, this study suggests that TNF-α is present in early human milk in sufficient quantities to exert possible biologic effects upon the mammary gland of the mother or the immune system of the infant.

Collection of fore and hind milk from the sow and the changes in milk composition during suckling.

Abstract: A new sampling method for the collection of fore and hind milk from the sow has been developed which resembles normal milk removal by the piglet, yet overcomes the difficulties of collecting milk that is available for only a short time (10-20 s) at each let-down. Samples of hind milk were collected immediately after the completion of a successful sucking, while the fore milk was collected at the beginning of the next natural let-down. Modification of existing assays for fat, protein and lactose was required to provide rapid analysis of the small volumes (less than 0.5 ml) of milk collected using this procedure, and these methods were validated by comparison with reference methods. Total solids and the concentration of fat in whole milk, and protein and lactose in skim milk, were measured in fore and hind milk collected from 4, 20, 12 and 12 sows respectively, 6-11 d post partum. For fore milk, the results (mean +/- SD (n)) were: total solids, 199.9 +/- 9.9 g/l (8); fat, 96.7 +/- 13.9 g/l (41), protein, 47.7 +/- 4.5 g/l (27) and lactose, 58.3 +/- 4.0 g/l (27). In hind milk, there was a significant increase in the concentration of fat (15.3 g/l, P less than 0.001, n = 41) which was reflected by a significant increase in total solids (14.7 g/l, P less than 0.001, n = 8) and calculated energy (511 kJ/l, P less than 0.001, n = 27), but there was no significant difference in the concentration of either protein or lactose. This increase in milk fat during milk let-down is in contrast to the results of most previous studies in the sow and is discussed in terms of the possible mechanisms that may cause the concentration of fat to increase as milk is removed from the mammary gland.

Aflatoxrn M1 in human breast milk from The Gambia, West Africa, quantified by combined monoclonal antibody immunoaffinity chromatography and HPLC

Abstract: Maternal-to-child exposure of aflatoxin Ml in breast milk is an underevaluated risk factor from dietary exposure to aflatoxin B1. A molecular dosimetry study in the Gambia West Africa was initiated to explore the relationships between dietary intake of aflatoxins during a 1-week period and a number of aflatoxin biomarkers including aflatoxin metabolite excretion into breast milk. For the breast milk study 5 lactating women were identified and milk samples were collected by hand expression once a day during days 3-7 for 3 women and during days 3-6 for the 2 other women. Aflatoxin M1 (AFM1) in human milk was measured in all 5 subjects by a preparative monoclonal antibody immunoaffinity column/HPLC method. In 3 of 5 women aflatoxin G1 was found. Estimates of the percentage of aflatoxin in the diet excreted as AFM1 in milk ranged from 0.09% to 0.43%. Thus these data indicate that a rapid methodology exists to assess the levels of AFM1 excretion in human milk and to use this approach as a biomarker for exposure of children to this carcinogen. (authors)

Developmental and environmental regulation of a mammary gland-specific nuclear factor essential for transcription of the gene encoding beta-casein.

Abstract: During the lactation period, mammary epithelial cells secrete large amounts of milk proteins. The coordinate regulation of milk protein expression is effected by the lactogenic hormones. We have investigated the activity of a mammary gland-specific transcription factor (MGF), which mediates hormonal influences at the level of a milk protein gene promoter. MGF-binding sites are present in the promoters of the most abundantly expressed milk protein genes. Mutation of the MGF-binding site in the beta-casein gene promoter completely abolishes responsiveness of the promoter to lactogenic hormones in cultured mammary epithelial cells. MGF activity is closely controlled in vivo. High MGF levels were found in mouse mammary gland nuclear extracts toward the end of pregnancy and during lactation. Withdrawal of suckling pups from their mothers during the lactation period caused a strong and rapid decrease of MGF activity. Readdition of pups to their mothers restored maximal MGF levels within 4 hr. We investigated MGF phosphorylation as a possible posttranslational modification responsible for regulation of the DNA-binding activity of MGF. Treatment of nuclear extracts from lactating mammary glands with potato acid phosphatase abolished MGF-binding activity. Casein kinase II phosphorylation of nuclear extracts from animals withdrawn from their pups for 24 hr enhanced MGF-binding activity. These results suggest that the reversible activation of MGF by suckling and withdrawal might be mediated by the action of kinases and phosphatases.

Alterations in Hypothalamic- Pituitary Responsiveness during Lactation

Abstract: Lactation is a unique event among mammals in which a tight behavioral bonding between individual animals is coupled with physical transfer of essential nutrients. Disruption of this partnership would result in the death of the infant, and, if widespread, the disappearance of the species. It is not surprising, therefore, that there are major physiological as well as psychological adaptations in the nursing mother. Suckling is associated not only with the release of prolactin and oxytocin,' but also with increased ACTH and corticosterone.24 Glucocorticoids are indeed important for the maintenance of la~tation,~ and instead of the marked diurnal variation of corticosterone Seen in males and cycling females, lactating rats have a markedly diminished early morning nadir in corticosterone levels and slightly reduced peak levels.6 The lack of low corticosterone levels during the morning may, at least in part, be related to suckling-induced release of corticosterone, because 24 hours after removal of their litters corticosterone falls to levels similar to those in nonlactating controls.6 In marked contrast to the evidence for increased levels of corticosterone during lactation, plasma corticosterone responses to stress are markedly decreased in lactating rats.' One possible reason for this could be a chronic increase in feedback signals either at hypothalamic corticotrophin-releasing hormone (CRH) or pituitary corticotrophin (ACTH) levels of the hypothalamic-pituitary-adrenal (HPA) axis by the elevated mean plasma corticosterone levels. To test this, we have investigated the ACTH rhythm in both lactating mothers and age-matched virgins in the absence of corticosterone feedback following adrenalectomy.8 As expected, the sham-adrenalectomized virgin females had a normal ACTH and corticosterone rhythm, and the adrenalectomized virgins maintained a strong ACTH rhythm. The lactating mothers, however, had no ACTH rhythm even after adrenalectomy. Since lactating rats lose their diurnal regulation of ACTH secretion even in the absence of circulating corticosterone, there is clearly a corticosterone-independent mechanism that overcomes the normal circadian input, presumably at hypothalamic level. In a further series of lactating rats and age-matched controls, adrenalectomy was coupled with corticosterone replacement using subcutaneous pellets. This resulted in consistent plasma levels of corticosterone throughout the 24 hours, with plasma concentrations depending on the percentage of corticosterone in the implanted pellets. There were highly significant negative correlations between plasma ACTH and coxtiassterone in both virgins and lactating mothers. Although lactating mothers were less sensitive to corticosterone feedback on ACTH secretion at all times, both virgins and mothers were more sensitive to corticosterone in the morning than in the evening. This maintenance of diurnal sensitivity to corticosterone feedback was also paralleled in further stress studies. These clearly demonstrated that in spite of the blunting in the

Lactation characteristics of nine breeds of cattle fed various quantities of dietary energy.

Abstract: Milk yield data were collected by weigh-suckle-weigh procedures at approximately 14, 28, 56, 84, 112, 138, 156, 184, and 212 d postpartum for mature Angus, Braunvieh, Charolais, Gelbvieh, Hereford, Limousin, Red Poll, Pinzgauer, and Simmental cows over a 4-yr period. Individual cows were fed at one of four energy intake levels. Parameters characterizing lactation curves for 431 lactations from 179 cows were estimated by nonlinear regression. Differences due to breed, level of energy intake, and the two-factor interaction between breed and level of ME allow- ance for scale and shape parameters of lactation curves and derived estimates for time of peak lactation, yield at time of peak lactation, and for total yield for a 210-d lactation period were evaluated. Breed and energy intake level were significant sources of variation for all traits. Pooled over energy levels, daily yields at time of peak lactation of Braunvieh, Gelbvieh, and Pinz- gauer were greater (P < .05) than those of Angus, Charolais, Hereford, and Limousin. Simmental and Red Poll were intermediate. Total lactation yield of the Braunvieh exceeded (P < ,051 that of all other breeds with the exception of Gelbvieh. Hereford produced less milk than (P c ,051 the other breeds. The response in yields at time of peak lactation as energy allowances increased for Braunvieh, Charolais, Gelbvieh, Limousin, and Pinzgauer cows was linear and resulted in higher yields at this time. Linear increases in total 210-d yield and times of peak lactation were observed for all breeds with the exception of Hereford.

The role of growth hormone, prolactin and insulin-like growth factors in the regulation of rat mammary gland and adipose tissue metabolism during lactation

Abstract: Inhibition of prolactin secretion with bromocriptine and neutralization of GH action with a specific antiserum to rat GH (rGH) were used to explore the modes of action of GH and prolactin in maintaining lactation in the rat. Treatment of dams with anti-rGH caused a small reduction in litter weight gain whilst bromocriptine reduced litter weight gain by 50%. When both treatments were combined, however, milk yield ceased completely and this was accompanied by a wide variety of effects on mammary lipid metabolism including decreases in the mRNA concentrations of acetyl CoA carboxylase, fatty acid synthase, malic enzyme and lipoprotein lipase. Activities of acetyl CoA carboxylase and lipoprotein lipase were also significantly reduced. Reciprocal changes were evident in adipose tissue with increases in acetyl CoA carboxylase and lipoprotein lipase activities. In conjunction with a decreased lipolytic response to noradrenaline in adipose tissue of animals given the combined treatment of bromocriptine and anti-rGH, this represented a co-ordinated series of changes to reduce lipid synthesis in the mammary gland and enhance lipogenesis and triglyceride storage in adipose tissue as milk production ceased. All of these effects could be prevented in part by concurrent treatment with GH, but insulin-like growth factor-I (IGF-I) and IGF-II failed to affect any of the parameters measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Parathyroid hormone-related protein: a possible endocrine function in lactation.

Abstract: OBJECTIVE Parathyroid hormone-related protein (PTHrP), initially discovered as the factor responsible for the syndrome of humoral hypercalcaemia of malignancy, has also been found to be expressed in placenta, in pregnant uterus, in the fetus at many locations, and in the lactating mammary gland. This study sought to establish whether PTHrP reaches the maternal circulation when it is expressed in mammary tissue during lactation or in the maternal reproductive tract during gestation. DESIGN Blood samples were collected from 53 subjects: 18 pregnant women in all stages of gestation, 19 lactating mothers and 16 non-lactating post-partum controls. MEASUREMENTS PTHrP was measured using a specific and validated radioimmunoassay. Parathyroid hormone was measured by two-site immunoradiometric assay. Total calcium was measured by atomic absorption spectre-photometry. RESULTS Circulating levels of PTHrP were readily detectable in 12 of 19 nursing mothers (range 2.7–7.8 pmol/1) but in none of the mothers who were bottle feeding. PTHrP was also detected in one of 18 pregnant subjects. Parathyroid hormone concentrations were lower in lactating mothers (2.3 ± 1.0 pmol/1), than in non-lactating mothers (3.5 ± 1.2 pmol/1) (P <0.01). CONCLUSION PTHrP reaches the maternal circulation during lactation in amounts which could produce a systemic effect.

Prolonged lactation contributes to depletion of maternal energy reserves in Filipino women.

Abstract: This paper identifies determinants of women's postpartum weight and weight change in a large group of Filipino women followed for 24 mo. Longitudinal, multivariate models focused on the effects of lactation, while controlling for energy intake, energy expenditure, reproductive history and seasonality. Lactation was found to have a significant negative effect on weight of urban women. The negative effects of lactation increased with the intensity and duration of breast-feeding. Among rural women negative effects of lactation on weight were observed only after 10-14 mo. Models of net postpartum weight change (from 2 to 24 mo) among nonpregnant women confirmed an important role for lactation. The likelihood of weight loss was significantly increased by lactation of more than 12-mo duration, by greater maternal age and by low dietary energy intake. The effects of lactation on maternal energy reserves can be mitigated substantially be increasing maternal dietary energy intakes.

Expression of alpha-lactalbumin, alpha-S1-casein, and lactoferrin genes is heterogeneous in sheep and cattle mammary tissue.

Abstract: We used 35S-labeled cRNA probes to localize the sites of alpha-lactalbumin, alpha-S1-casein, and lactoferrin mRNA synthesis in sheep and forcibly weaned cattle mammary tissue. Expression of alpha-lactalbumin was absent in three of four "virgin" glands studied, present in some alveoli of "pregnant" glands but not in others, despite a similar histological appearance. In the early lactating gland, expression was high in those alveoli with few fat globules in their cells and lumen and was absent in alveoli with abundant fat globules. These observations suggest either that alpha-lactalbumin gene expression is linked to the long-term secretory activity of cells and falls once cells are resting or regressing, or that there are cyclical variations in expression, or that in the lactating gland some groups of epithelial cells are synthesizing alpha-lactalbumin and some are synthesizing fat. Expression patterns of alpha-S1-casein were similar to those of alpha-lactalbumin. Lactoferrin, in contrast, was expressed almost exclusively in the "fatty alveoli" of both species. Our results show that dramatic variations in milk gene expression can occur throughout the mammary gland of sheep and cattle and that at no stage of pregnancy, lactation, or involution can the gland be considered metabolically homogeneous.

Acute prolactin and oxytocin responses and milk yield to infant suckling and artificial methods of expression in lactating women

Abstract: Breast-feeding is today the major form of infant nutrition in the immediate postpartum period. Despite this, recent trends in modern life-styles have raised obstacles to successful lactation. These include infant illness and maternal responsibilities outside the home, both requiring separation from the mother. While the hormonal dynamics of infant suckling are understood, little is known about the effects of artificial methods of milk expression. A variety of breast pumps exist in the current US market which vary considerably in price and effectiveness. To understand better the ability of these pumps to assist women in the maintenance of lactation, the current study was undertaken to evaluate their effects on milk yield and prolactin and oxytocin release when compared to natural infant suckling. Twenty-three women who were exclusively breast-feeding their infants were randomly assigned to serially use several pumping methods, as well as infant suckling, with blood being taken at 10-minute intervals to determine the hormonal responses. The results reveal variability in the prolactin responses to the artificial pumping methods, with the greatest responses found with an electric pulsatile pump; these responses compare favorably with those of natural infant suckling. Other methods were less successful in causing prolactin elevations. No differences were seen among the methods in the oxytocin response. The results of this study demonstrate striking differences in the ability of breast-pumping methods to produce an acute and sustained prolactin rise in breast-feeding mothers. The large discrepancies found suggest the need for further studies in to enable women and health care providers to choose the most appropriate method for milk expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of feed intake during lactation and after weaning on sow reproductive performance

Abstract: To study the effects of feed intake during lactation and after weaning on reproductive performance, 89 second-parity Lacombe sows were allowed 6 kg feed d−1 (H) or were restricted to 3 kg feed d−1 (R) during lactation and during the weaning to estrus interval (WEI); this resulted in a 2 × 2 factorial design (groups HH, HR, RH and RR). To minimize the confounding effects of duration of WEI on sow performance, the experiment was terminated 10 d after weaning. The diet was formulated to provide 12.4 M J ME kg−1 and 16% crude protein. Restricted feeding during lactation resulted in a longer (P < 0.05) WEI (7.3 d vs. 5.9 d). WEI was not affected by feed intake after weaning. Fewer (P < 0.05) sows feed restricted during lactation exhibited estrus by 10 d from weaning (31.8% vs. 88.9%). Ovulation rate was not affected by lactation or postweaning feed intake. However, embryo survival at 25 d of gestation was influenced (P < 0.05) by feed intake during both periods. The highest embryo survival (85%) was in HR sows...

Relaxin increases the firing rate of supraoptic neurones and increases oxytocin secretion in the rat.

Abstract: In urethane-anaesthetized ovariectomized rats, injection of porcine relaxin (7.5 and 15 micrograms/kg, i.v.) caused a sustained increase in circulating plasma oxytocin and vasopressin concentrations; 10 micrograms relaxin/rat i.v. produced a smaller but significant increase in plasma oxytocin concentration in conscious ovariectomized rats. A significant increase in oxytocin concentration and inhibition of the spontaneous milk-ejection reflex was also seen in anaesthetized (ovary intact) lactating rats following injection of relaxin (7.5 micrograms/kg, i.v.). To investigate whether relaxin acts by increasing the electrical activity of oxytocin neurones or by facilitating stimulus-secretion coupling in the pituitary, the electrical activity of neurones in the supraoptic nucleus was recorded in urethane-anaesthetized lactating rats and in ovariectomized rats. Porcine relaxin (10 micrograms/rat, i.v.) increased the firing rate of both oxytocin and vasopressin neurones in the supraoptic nucleus in lactating rats. The response to relaxin was unaffected by subsequent injection of naloxone (1 mg/kg, i.v.). Oxytocin neurones were also activated by injection of relaxin (10 micrograms/rat) into ovariectomized rats. Combining the electrophysiological data, the neuronal activation following relaxin was significantly correlated with the level of spontaneous activity prior to relaxin injection. The results show that relaxin acts centrally to increase circulating plasma oxytocin and vasopressin concentrations by an opioid-independent mechanism.

Production of parathyroid hormone-related protein by the mammary gland of the goat

Abstract: Parathyroid hormone-related protein (PTHRP) has been quantified by sensitive specific immunoassays in mammary venous blood and milk from 7 days before to 7 days after parturition in the goat A significant venous-arterial concentration gradient in plasma PTHRP 1-86 concentrations was demonstrated across the mammary gland, indicating that PTHRP enters the maternal circulation and may have a role in calcium homoeostasis during lactation Significant and sustained increases in mammary venous and milk PTHRP 1-86 concentrations were found from 1 day before parturition to 7 days afterwards, with peak concentrations of 157 +/- 058 pmol/l (plasma) and 869 +/- 295 nmol/l (milk) (mean +/- SEM) occurring on day -1 and the day of parturition respectively Estimates of the mammary output of PTHRP into plasma in four goats averaged 9% (range 1-25%) of that secreted into milk Suppression of maternal prolactin concentrations by bromocriptine significantly reduced milk yield and the mammary venous PTHRP concentration, without affecting the concentration of PTHRP in milk In conclusion, parturition in the goat is associated with a sustained increase in secretion of PTHRP into both plasma and milk; the former may be involved in maternal calcium homoeostasis, whereas the latter may have a role in the neonate

Functional aspects of maternal aggression in mammals

Abstract: Evidence from several species of mammals suggests that the observed increase in female aggressiveness during lactation is aimed at protecting offspring from conspecifics. Whereas in rodents materna...

Regulation of mammary growth and function by TGF-beta.

Abstract: We have previously shown that TGF-beta 1 rapidly and reversibly inhibits ductal growth in vivo when administered by miniature slow-release plastic implants. A possible role for endogenous TGF-beta 1 was suggested by the observation that the normal gland displayed substantial, developmentally regulated levels of TGF-beta 1 transcripts and protein. These studies have now been extended to include the other two mammalian TGF-beta isoforms. When tested with slow-release plastic implants, TGF-beta 2 and TGF-beta 3 also caused disappearance of the proliferating mammary stem cell layer, with rapid involution of ductal end buds and cessation of glandular growth. None of the isoforms was active in inhibiting alveolar morphogenesis. We conclude that under the conditions of these tests, the three mammalian isoforms are functionally equivalent. However, striking differences in patterns of gene expression and in the distribution of immunoreactive peptides suggest that TGF-beta 2 was expressed only at low levels, and mainly during pregnancy. TGF-beta 3 was expressed in ductal stroma and epithelium, and was the only isoform detected in myoepithelial cells. Developing alveolar tissue and its associated ducts displayed striking TGF-beta 3 gene expression and immunostaining, which were greatly reduced during lactation. We are now investigating the possibility that the observed high levels of TGF-beta expression in pregnancy, particularly of TGF-beta 3, and the absence of substantial expression of any isoform during lactation, may indicate a role for the TGF-beta in regulating functional differentiation or the onset of milk secretion.