Abstract
Summary
Thoracic teats of rats were ligated and litters were adjusted to 2 or 6 pups on day 2 of lactation. Rats were constantly with their litters until day 7 of lactation when they were subjected to: (i) continued suckling; (ii) 12.5 hr nonsuckling; or (iii) 12.0 hr nonsuckling then 0.5 hr suckling.
Plasma corticosterone (μg/100 ml) of rats suckling 2 or 6 pups was 23.83 and 29.31, respectively, when litters suckled continuously. It was reduced to 19.75 and 20.15, respectively, following 12.5 hr of nonsuckling. Following 12 hr nonsuckling, 0.5 hr of suckling increased plasma corticosterone to 39.44 and 70.01 μg/100 ml in rats with 2 and 6 pups, respectively. Corticosterone released in response to suckling appeared to be related to intensity of the suckling stimulus.
Rats suckling 6 pups had more mammary ribonucleic acid (RNA), deoxyribonucleic acid (DNA), and a greater RNA/DNA ratio than rats with 2 pups. Mammary gland RNA and RNA/DNA ratio decreased after 12.5 hr nonsuckling and mammary weight increased 88.1 and 15.7%, respectively. These results suggest that the accumulation of milk can directly supress the protein synthesizing capacity of the mammary gland.
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