Search

Various synthetic glucocorticoids reduced binding of tritiated Cortisol and tritiated dexamethasone to 700× g supernatant and precipitate fractions of mammary tissue slices from lactating cows. Unlabeled progesterone, testosterone, and 17 β -estradiol had no effect on tritiated glucocorticoid binding in mammary tissue slices. Cortexelone, Cortisol, triamcinolone, and dexamethasone inhibited [carbon-14] glucose incorporation into mammary tissue slices from lactating cows in a dose response relationship. Glucocorticoid binding to 700× g supernatant and precipitate fractions of mammary tissue was correlated with the ability of glucocorticoids to reduce [carbon-14] glucose uptake into 700× g supernatant fractions of mammary tissue slices from lactating cows. In experiments designed to measure mammary uptake of glucocorticoids, the differences in concentration of total glucocorticoids between external pudic artery and mammary vein were greatest at 6 (5.8ng/ml) and 12 (2.9ng/ml) min after the start of milking. These intervals correspond to the times when glucocorticoid concentrations in serum were maximal after application of the milking stimulus. We conclude that glucocorticoid uptake and binding are associated with lactational events.

SummaryInsulin averaged 2.6 ng/ml in mammary arterial and venous sera collected from 30 min before to 70 min after milking of cows lactating 5-12 weeks. During the same period in cows lactating 37-57 weeks insulin increased to 3.5 ng/ml. Milking did not affect insulin concentrations during early or late lactation. Arteriovenous (A-V) differences averaged 0.17, 0.14 and 0.22 ng/ml for 30 min before, 0-20 min after and 30-70 min after milking. Stage of lactation (and yield of milk) did not affect A-V differences. Mammary uptakes of insulin averaged 1.6 and 1.4 μg/min in early and late lactating cows, respectively. Maintenance of uptakes of insulin may be associated with uptake of metabolites essential for maintenance of lactation.

The influence of periparturient secretion of PRL on cytological differentiation of mammary epithelial cells was studied in 17 multiparous, monotocous Holstein cows. Mammary tissue was obtained 10 days prepartum and 10 days postpartum from untreated cows and from cows treated with CB154 (2-Br-alpha-ergokryptin) or CB154 plus PRL. CB154 was administered from 12 days before expected parturition through 10 days postpartum to reduce serum PRL concentrations, whereas exogenous PRL was administered for 6 days during the periparturient period to mimic the normal periparturient surge of the hormone. On day 10 postpartum, mammary epithelial cells of cows given CB154 alone were classified 18% undifferentiated, 65% intermediately differentiated, and 18% fully differentiated. In contrast, there were no undifferentiated epithelial cells in either postpartum controls or cows treated with CB154 plus PRL, and 73% and 79% of epithelial cells, respectively, were fully differentiated. Ultrastructural analysis demonstrated a relative lack of cellular differentiation in cows given CB154 alone. Specifically, the rough endoplasmic reticulum occupied 24% and 27% of the epithelial cell area in postpartum controls and cows treated with CB154 plus PRL, respectively; but the rough endoplasmic reticulum occupied only 16% of the cellular area in cows treated with CB154 alone (P less than 0.01). The relative area occupied by Golgi membranes and vacuoles was approximately 11% lower (P less than 0.01) in cows treated with CB154 than in lactating controls or cows that received PRL replacement therapy. The data demonstrate that periparturient secretion of PRL is necessary for complete structural differentiation of bovine mammary alveolar epithelium.

Mammary tissue from five cows was cut into pieces approximately 3 mm2 x .2 mm and placed subcutaneously in athymic mice (10 to 12 pieces/mouse). After 30 d, all mice were injected for 10 d with 17 beta-estradiol (1 microgram), progesterone (1 mg), ovine prolactin (1 mg), and growth hormone (recombinant DNA-derived bovine) (1 mg). Four grafts were then removed from each mouse, mice were ovariectomized, and subsequently mice were injected daily for 7 d with hydrocortisone (.2 mg, all mice), growth hormone (0, .25, .5, or 1.0 mg), and 0 or .5 mg ovine prolactin (three mice/treatment per udder). alpha-Lactalbumin content of grafts was 36 +/- 9 micrograms/mg DNA after treatment with estradiol, progesterone, growth hormone, and prolactin but before hydrocortisone, prolactin, and growth hormone treatment. Hydrocortisone treatment increased alpha-lactalbumin to 147 micrograms/mg DNA. Growth hormone plus hydrocortisone treatment increased alpha-lactalbumin to 391, 451, and 480 micrograms/mg DNA for .25, .5, and 1.0 mg/d of growth hormone, respectively. Prolactin plus hydrocortisone treatment increased alpha-lactalbumin to 466 micrograms/mg DNA. With exogenous prolactin, growth hormone increased alpha-lactalbumin content of grafts to 581, 647, and 689 micrograms/mg DNA for .25, .5, and 1.0 mg/d of growth hormone, respectively. Histological examination of tissues indicated that the effect of growth hormone was not mediated through increased epithelial area. Data suggest that bovine mammary tissue is capable of organotypic differentiation in athymic mice.

SummaryIntensive nursing (6 pups/6 intact abdominal-inguinal mammary glands, and replacing all 16-day-old litters every 4 days with 12-day-old foster litters) failed to prevent significant declines in mammary DNA, RNA, and litter weight gains between days 20 and 36 of lactation. But no comparable changes in lactic acid content of mammary glands were observed. Intense nursing maintained pituitary prolactin during extended lactation but ACTH decreased 67.6%. Thus, ACTH may be rate limiting to milk synthesis during extended lactation.

SummaryIncreasing the nursing frequency in rats from non-nursed levels (controls) to Ix, 2x, 4x and ad libitum frequencies progressively increased mammary DNA, RNA and pituitary prolactin content 4.3-, 21.1-and 2.1-fold, respectively. Pituitary ACTH content, although always detectable, was unaffected by nursing frequency.

SummarySeventy-two female rats were randomly allotted to three groups and mated at average ages of 44, 63, and 82 days. One half of each age group was killed at parturition and the other one half at day 16 of lactation. Although rats in the youngest age group weighed less than those in the other two groups at each weighing, these age and weight differences did not significantly affect litter weight or number of pups per litter at birth. The oldest rats had more total mammary DNA at parturition, but no significant difference existed by the 16th day of lactation. Total RNA doubled during lactation for all three age groups, but there was no significant difference among age groups at parturition or at day 16. Average litter weight gains were not significantly affected by age at mating, indicating that rats bred as early as 40 days of age lactated and raised litters as well as rats bred after 60 days of age.

SummaryDaily injection of 1 or 10 mg of prolactin for 10 days or transplantation of anterior pituitaries (AP) to the kidney capsule for 14 days markedly decreased pituitary weight and prolactin content of mature virgin rats. Ovariectomy reduced prolactin content of pituitaries relative to intact controls, but ovariectomy plus transplantation of AP's reduced prolactin content even further. These results indicated that function of the auto-feedback control of prolactin can occur without the ovary. Prolactin injections and AP transplants increased total mammary DNA and RNA, but these increases were somewhat reduced in ovariectomized rats compared with intact rats. Exogenous prolactin reduced uterine and adrenal weights, stimulated body weight increases but had no significant effects on ovarian weights.

Lactating Holstein cows received 0 (saline), 5, or 10 mg 9α FFA immediately following morning milking. Thereafter blood samples were collected hourly until completion of the evening milking 10 hours later. Treatment with 9α FFA resulted in a linear increase in plasma glucose during post-treatment (P 0.10). Direct microscopic measurements of somatic cell content of fore, primary and residual milk revealed no significant (P > 0.10) effect of 9α FFA on number of total somatic cells, granulocytes, agranulocytes, or epithelial cells. These results suggest that corticoid-induced leukocytosis of blood is not reflected by increased somatic cell numbers in milk.

SummaryMammary and uterine development and their relationships to the pituitary content of prolactin and LH were studied during the five estrous cycles after vaginal opening in rats. Cumulative mammary and uterine growth was completed largely by the fourth estrous cycle after puberty. Although there was a lag of 1 day between peak mammary and uterine development, virtually all of this growth occurred during the estrogenic phase of the estrous cycle. Involutionary changes occurred in both organs during the progestational phase of the estrous cycle. Pituitary prolactin concentration was greater at proestrus (0.032 IU/mg) and metestrus (0.041 IU/mg) than at estrus (0.015 IU/mg) or diestrus (0.015 IU/mg). Pituitary LH concentration, which averaged 0.72, 0.31, 0.27, and 0.33 μ/mg at proestrus, estrus, metestrus, and diestrus, respectively, was correlated (r=0.58, p

The levels of progesterone (P) and estradiol-17 β (E) necessary for maximal udder development were studied in 30 ovariectomized heifers. The two hormones were injected three times weekly for 20 weeks. Growth measurements were estimated from mammary weight, DNA, maximal volume, and histological rating; RNA and RNA/DNA values were also determined. The optimal combinations appeared to be either 200mg P and 800 μ g E or 100mg P and 400 μ g E. These doses produced tightly packed alveolar cells very similar to those of normally developed udders from five-month-pregnant heifers. None of the steroid combinations stimulated precocious milk secretion. A discrepancy between nucleic acid values and histological ratings of the udders was observed. It is suggested that several criteria be used to evaluate hormone-induced mammary development.

SummaryAdrenal corticosterone content and concentration decreased linearly from days 16 to 32 of lactation. Peripheral plasma concentrations of corticosterone in lactating rats were higher than the resting levels measured in virgin rats. However, corticosterone concentrations in plasma did not change significantly between days 16 and 32 of lactation. Rats killed at day 32 of lactation had a greater plasma corticoid binding globulin (CBG) activity than rats killed at days 16 and 24. Adrenal corticosterone content was correlated significantly with mammary gland RNA, DNA, and litter weight gain. The data support the concept that adrenal secretions may be rate limiting to milk synthesis during prolonged lactation.