Abstract
Summary
Rats nursing either six or ten young on six abdominalinguinal mammary glands, were sacrificed on days 5, 10, 15 and 20 postpartum. Nucleic acid measurements were made on the mammary glands and explants were prepared and incubated with radioactive precursors. Incorporation of 14C acetate into tissue triglycerides, 14C glucose into lactose, and 14C leucine into tissue casein per milligram DNA for 4 hr was used as an index of secretory activity. Dams nursing ten young did not have higher mammary gland weights, mammary gland nucleic acid contents or secretory activity measurements than those nursing six young. Mammary gland RNA and DNA contents increased with advancing lactation. Acetate incorporation into triglycerides was higher on day 15 of lactation than at other times. Plasma prolactin was higher on days 5 and 10 of lactation than day 20. The variable most highly correlated with pup weight and pup gain was mammary gland weight.
Mammary gland DNA content accounted for 5.8% of the total variation in pup weight. Addition of one measure of leucine, acetate or glucose incorporation to DNA content increased the variation accounted for to 13.8-17.4%. The addition of RNA content, total leucine, total acetate, and total glucose incorporation to the mammary gland DNA values increased the variation for pup weight accounted for to 30.9%. The variation accounted for in pup gain by these variables was less than for pup weight. These results indicate that both DNA content and secretory activity of mammary glands play a significant role in accounting for variation in pup weight and pup gain.
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