Mammary development in mice: effects of hemihysterectomy in pregnancy and of litter size post partum

Abstract

SUMMARY1. Mice were hemihysterectomized on day 8 of pregnancy to reduce the number of feto-placental units.2. Fetal mortality was not affected by hemihysterectomy; mean single-pup weight at birth was increased when compared with sham-operated controls.3. Pregnant sham-operated and hemihysterectomized animals were killed on days 13 and 18 of gestation, and their mammary glands were analysed for total DNA (DNAt) and RNA (RNAt). Both were significantly lower in the hemihysterectomized group on day 18, but not on day 13. 4 Milk yield was assessed, by daily weighing ofthe litter, in groups ofsham-operated and hemihysterectomized lactating animals suckling nine pups each. There was no difference in yield between the two groups.5. One group ofsham-operated mice suckling nine pups, one ofhemihysterectomized mice suckling nine pups and one of hemihysterectomized mice suckling four pups were killed on day 5 of lactation for mammary gland analysis. There was no significant difference in mammary weight or DNAt between the sham-operated and hemihysterectomized animals suckling nine pups, although RNAt was still reduced in the latter. Mammary weight, DNAt and RNAt were all significantly lower in the hemihysterectomized group suckling four pups than in either of the other two groups.6. It is concluded that the less well developed mammary glands of mice which give birth to small litters are capable of compensatory growth during the first few days of lactation if a sufficiently strong suckling stimulus is given.7. It is suggested that control of mammary development by the fetus during gestation and by the suckling young during early lactation are both mechanisms designed to ensure that milk yield is appropriate to the needs of the young.

Compensatory changes in mammary development and function after hemimastectomy in lactating goats

“…A similar observation was reported for guinea-pigs by Kuosaite (1965), although others have been unable to repeat this (Linzell, 1963;Knight & Peaker, 1981). In mice, mammary development was reduced during gestation by hemihysterectomy, presumably as a result of decreased circulating levels of placental lactogen (Knight & Peaker, 1982b) and by short periods of fasting (Knight & Peaker, 1982c). In both cases compensatory growth of the gland occurred during early lactation, resulting in a normal milk yield.…”

Mammary Development and Regression During Lactation in Goats in Relation to Milk Secretion

“…i.v. ) (Knight & Peaker, 1982b Accuracy of biopsy technique Measurements were made in three goats which were being used for other studies. One mammary gland was surgically removed from each goat at peak lactation (week nine) and the second gland was removed post mortem during late lactation (week twenty-eight).…”

Metabolic adaptations in goat mammary tissue during pregnancy and lactation

“…DNA was measured in freshly-prepared tissue homogenates by the diphenylamine method (Knight & Peaker, 1982c) and in expiant homogenates by a fluorometric method (Labarca & Paigen, 1980) using bovine thymus DNA as a standard. There was no significant difference between the results obtained with the two methods.…”