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DIFFERENCES BETWEEN MICE GESTATING AND LACTATING AT 21° AND AT 34°–36° WITH PARTICULAR REFERENCE TO THE MAMMARY GLAND
Author(s) -
Pennycuik Pamela R
Publication year - 1966
Publication title -
australian journal of experimental biology and medical science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.999
H-Index - 104
eISSN - 1440-1711
pISSN - 0004-945X
DOI - 10.1038/icb.1966.39
Subject(s) - lactation , mammary gland , weaning , biology , endocrine system , histology , pregnancy , gestation , uterus , endocrinology , medicine , hormone , andrology , physiology , zoology , genetics , cancer , breast cancer
Summary Pup survivals, weaning weights, mammary gland histology and composition, carcase composition and endocrine weights were examined at various stages of the reproductive cycle in mice reared at 21° and at 34° and in mice adapted as adults to 36°. Mice gestating at 36° lost their entire litters during the first 2 days of extra‐uterine life. At 34° mice were able to rear their litters, but the weight gains up to weaning were not as great as those for pups reared at 21°. The development of the alveolae and tubules in the mammary glands of mice gestating and lactating at 34° and at 36° lagged a little behind that of animals at 21°. By 18 days' gestation the quantity of secretory tissue formed by animals at higher temperatures was rather less than that of animals at 21°. During lactation the difference between the groups at 21° and 34° increased to such an extent that by 35 days the mice at 34° had only ⅔ of the amount of secretory tissue of those at 21°. Fat stores in the mammary fat pad and in the whole animal rose during pregnancy in mice at 21° and at 34° and 36°. During lactation fat stores fell abruptly in the animals at 21° and more slowly in animals at 34°. The ultimate level reached was the same in both cases. At 21° maternal fat free tissue (excluding the uterus and the posterior mammary glands) increased in amount during the last third of pregnancy and the early stages of lactation. This weight gain during pregnancy was also observed in mice at 34° but the gain during lactation was reduced. At 36° the weight gain during pregnancy was missing. Although these gains were significant, particularly in animals at 21°, they were small in comparison with the changes in live weight brought about by variations in the weight of the uterus and its contents and by variations in the amount of food held in the gut. The response of the weights of pituitary, ovaries and adrenal glands to pregnancy and lactation were similar for mice at 21°, 34° and 36°. At 21° the thyroid weight showed a significant drop during the perinatal period. This change was not observed in animals at 36°.