Protein metabolism in the mouse during pregnancy and lactation.

Protein synthesis was measured in vivo in the whole body and in a number of individual tissues in mice at various stages of pregnancy and lactation. The absolute rate of protein synthesis in the whole body increased from 640 mg/day in virgin mice to 1590 mg/day by day 18 of pregnancy, and to 2100 mg/day by day 15 of lactation. Large proportions of these increments were contributed by the rapidly growing foetuses and placentae in the pregnant animals and by protein synthesis in the mammary glands during lactation. In addition, a substantial stimulation of growth and protein synthesis was also observed in the liver and the gastrointestinal tract. Gastrocnemius muscle showed no changes in protein metabolism, indicating that in the well-fed mouse this tissue is not required to play a role as a protein reserve during pregnancy and lactation.     

Intermittent suckling enables estrus and pregnancy during lactation in sows: effects of stage of lactation and lactation during early pregnancy

Previously we demonstrated that pre-ovulatory LH and post-ovulatory progesterone (P4) concentrations in plasma were low and embryo development was retarded when sows were induced to ovulate during lactation by submitting them to intermittent suckling (IS). The present study investigated whether this was due to: (1) stage of lactation when IS was initiated, and (2) continuation of IS post-ovulation. Multiparous Topigs40 sows were studied under three conditions: conventional weaning at Day 21 of lactation (C21; n = 30), intermittent suckling from Day 14 of lactation (IS14; n = 32), and intermittent suckling from Day 21 of lactation (IS21; n = 33). Sows were separated from piglets for 12 h daily during IS. IS sows were either weaned at ovulation or 20 d following ovulation. One-third (21/63) of the IS21 and C21 sows had already ovulated or had large pre-ovulatory follicles at Day 21 and were excluded from further study. Initiation of IS at Day 14 instead of Day 21 of lactation tended to reduce P4 at 7 d post-ovulation (P = 0.07), did not affect pregnancy rate, and tended to reduce embryo survival (P = 0.06). Continuation of IS during pregnancy resulted in lower P4 at 7 and 12 d post-ovulation, tended to reduce embryo weight and pregnancy rate (P < 0.10), whereas embryo survival was not affected. This study presents data for a population of sows in which follicle growth and ovulation are easily triggered under suckling conditions. Further, when these sows are bred during lactation, initiation of IS at 21 rather than 14 d of lactation with weaning at ovulation yields the most desirable reproductive performance.     

Metabolic adaptations during lactogenesis. Lactose synthesis in rabbit mammary tissue during pregnancy and lactation.

Lactose biosynthesis and relevant enzymatic activity in rabbit mamma ry tissue during various stages of pregnancy and lactation are investigated by using a tissue-slice incubation method in order to understand the temporal relationships. Ovulation was induced in 27 New Zealand white rabbits and they were bred by artificial insemination. Sacrifice occurred on days 15, 24, and 29 of pregnancy, and day 2, 5, 8, 15, and 22 post partum. Nucleic acids were extracted and concentratons of DNA determined spectrophotometrically at 600 nm with diphenylamine reagent and RNA determined with orcinal reagent. The tissue incubations were made with (U-14C) glucose. (14C) lactose was then separated by paper chromatography from unchanged radioactive glucose. Enzyme analysis including determining the activities of phosphoglucomutase, UDP-glucose pyrophosphorylase, and UDP-glucose 4-epimerase. Lactose synthase was determined, as well as, hexokinase. A biphasic adaptation in the rate of lactose synthesis and in the RNA concentration was noted during lactogenesis. The 1st increase in the rate of lactose biosynthes is occurred between days 15 and 24 of pregnancy. A 2nd substantial increase was noted immediately post partum. The overall rate of lactose biosynthesis increased 12-fold from day 24 of pregnancy to day 15 of lactation post partum, and then decreased from 15 to 22 days post partum. The RNA concentration/g wet weight of tissue and the ratio of RNA/DNA closely represented the biphasic ability of the mammary-tissue slice to synthesize lactose. Increases in the activities of UDP-glucose 4-epimerase and lactose synthase were most closely correlated with increases in the rate of lactose biosynthesis. UDP-glucose pyrophosphor ylase activity was unrelated with the ability to synthesize lactose, and hexokinase and phosphoglucomutase activities were variable during pregnancy and lactation. Lactose synthase activity was present by day 15 of pregnancy, but the ability to synthesize lactose was undetected until day 24 of pregnancy.     

Effect of some progestational steroids on lactation in Egyptian women. I. Milk yield during the first year of lactation.

The effect of monthly injectios of 300 mg Depo-Provera or 150 mg Deladroxone, and of daily oral administration of .5 mg chlormadinone acetate or .3 mg quingestanol acetate on lactation was studied in Egyptian women during the 1st year of lactation. Women receiving Depo-Provera had the highest milk yield, followed by those taking Deladroxone and quingestanol acetate. The milk yields while taking these hormonal preparations were higher than in untreated controls. However, those women taking chlormadinone acetate had lower milk yields than untreated controls. The increased milk yield is probably due to the progestagenic activity, and minimal estrogenicity, of these drugs.     

Leptin injection during lactation alters thyroid function in adult rats.

The aim of this study was to evaluate the effects of hyperleptinemia during the first ten days of life on thyroid function in adulthood. After birth, pups were separated into two groups: L8 - receiving daily injections of recombinant mouse leptin (8 microg/100 g body weight, sc) and control (C) - receiving the same volume of saline. Both groups were treated for the first 10 days of lactation. The animals were sacrificed at 150 days of age, and the blood was collected for leptin, TSH, total triiodothyronine (TT 3 ) and total thyroxin (TT 4 ) serum concentration determinations by radioimmunoassay. The thyroid gland was excised to determine thyroid iodine uptake. Leptin, TT 3 and TT 4 serum concentrations in L8 group were significantly (108 %, 47 % and 32 %; p < 0.05) higher than that of controls. There was no significant difference between the groups related to thyroid iodine uptake and TSH serum concentration. These data suggest that the first half of lactation period is important in determining thyroid function in adulthood, and that it can be programmed by serum leptin concentration.     

Prolactin binding in rat mammary gland during pregnancy and lactation.

Lactogenic hormones from the placenta and pituitary are primarily responsible for the growth and function of the mammary gland during pregnancy and lactation. In the present study we described the optimal conditions for the measurement of 125I-labeled ovine prolactin binding to mammary gland slices of pregnant and lactating rats. Prolactin binding is saturable (Kd approx. 2.36 - 10(-9) M), hormone specific and destroyed by proteases. The hormonal environments of pregnancy and lactation dramatically influence the availability and measurement of prolactin binding sites. Whereas binding consistently appears to be low in mammary glands removed from rats during pregnancy, binding levels rise 7--8-fold shortly after birth and remain high during the 22 days of lactation. However, the removal of the ovaries and gravid uteri at specific times during pregnancy results in a prompt 3--6-fold increase in prolactin binding. Elevated levels in potential prolactin binding capacity appear in mammary tissue coincident with the reported rise in serum rat placental lactogen between the eighth and eleventh days. We suggest that high levels of this lactogenic hormone promote the appearance of prolactin binding sites during pregnancy and mask the sites such that they are not available for measurement in vitro.     

Contraception with progestogens and progesterone during lactation

The growth and development of breastfed infants whose mothers used the contraceptive implants Norplant® containing levonorgestrel and the injectable containing norethisterone enanthate were studied. Each group comprised of 120 women who initiated the use during the 5th to 7th week postpartum and were compared with a similar number of IUD using mothers. The breastfeeding performance did not differ between groups. The infants of the three groups performed similarly as regards their physical growth and health as well as the time of acquisition of the various milestones of psychomental development. A vaginal ring releasing 10 mg of the “natural” progesterone per 24 h was tested in breastfeeding mothers. The continuous use of the ring produced a serum level of progesterone around 4 ng/ml. This was effective in augmenting lactational infertility even through the later phases of breastfeeding when such an effect starts to wane off. The use of the ring proved to be acceptable and had no ill-effect on breastfeeding or infant growth or health. Using the natural progesterone as a contraceptive adds a new measure of safety, since the amount of the steroid secreted in the mother's milk will not be effectively absorbed from the infant's gut. These studies suggest the possibility of using two new methods for breastfeeding mothers; Norplant and the progesterone vaginal contraceptive ring. These can be initiated early postpartum, whenever this is considered needed.     

Plasminogen activators in the mouse mammary gland. Decreased expression during lactation

The enzyme content and mRNA level for both urokinase-type and tissue-type plasminogen activators have been explored during the life cycle of the adult mouse mammary gland. Both enzymes were detected, and urokinase-type plasminogen activator was the predominant form. A marked decrease in enzyme content occurred in late gestation and was maintained throughout lactation; upon weaning, the enzyme content returned to the levels found in virgin mice. These effects were entirely accounted for by changes in the respective mRNA concentrations, which were determined with respect to both total tissue RNA and poly(A+) mRNA. Thus, plasminogen activator-catalyzed proteolysis may occur at high levels throughout the life cycle of the mouse mammary gland, except during lactation.     

Lipolysis in rat adipocytes during pregnancy and lactation. The response to noradrenaline.

1. Lipolysis has been measured in parametrial adipocytes from virgin, pregnant and lactating rats. 2. The basal rate and the maximal rate of lipolysis, the latter measured in the presence of noradrenaline and theophylline, remained constant between the three experimental categories, with the exception of a significant transient increase in the basal rate at parturition. 3. The noradrenaline-stimulated lipolysis rate rose above the virgin rate during pregnancy and fell below it during lactation; inclusion of adenosine deaminase in incubations abolished these differences in response to noradrenaline. 4. Cyclic AMP phosphodiesterase activity was lower in adipocytes during pregnancy and lactation than in virgin animals.     

Metabolism of sheep adipose tissue during pregnancy and lactation. Adaptation and regulation.

1. Changes in the mean volume, the rate of fatty acid and acylglycerol glycerol synthesis, the activity of lipoprotein lipase and the numbers and affinities of insulin receptors of subcutaneous adipocytes are reported for sheep at different stages of pregnancy and lactation. In addition, the serum concentrations of insulin, progesterone, prolactin, choriomammotropin, somatotropin, glucose, acetate, L-lactate, glycerol and unesterified fatty acids are reported for these sheep. 2. A switch from lipid accumulation to net lipid mobilization accompanied by a decline in the capacity for lipid synthesis, occurred at the onset of the last third of pregnancy. Net lipid mobilization continued during lactation. 3. The changes that occurred in the serum concentrations of the various hormones listed above are discussed in relation to their possible roles in the modulation of adipose tissue metabolism in sheep during pregnancy and lactation. The observations are compared with those from previous studies on the hormonal control of adipose tissue metabolism in the rat during pregnancy and lactation.     

Oxytocin levels during breast-feeding in established lactation

Serial blood samples were taken from eight lactating women while they were nursing their babies 1–4 months postpartum, and from four lactating controls while they were not nursing. The plasma was assayed for oxytocin by radioimmunoassay after extraction with activated Vycor glass powder. In the suckling mothers mean plasma oxytocin rose from 5.4 pg/ml before nursing to 13.0 pg/ml during nursing. Oxytocin levels changed rapidly from minute to minute, with individual peaks as high as 54 pg/ml. Oxytocin levels in the control mothers averaged 4.4 pg/ml.