AJP - Endocrinology and Metabolism, Vol 245, Issue 6 549-E554, Copyright © 1983 by American Physiological Society
Cyclic AMP changes in guinea pig mammary gland and milk
R. F. Loizzi
Cyclic AMP was measured in guinea pig mammary gland biopsies from
midpregnancy through lactation and in daily milk samples throughout
lactation. The results indicate that mammary gland cAMP levels rise sharply
in late pregnancy to a prepartum peak and then drop abruptly at partus.
This is similar to the pattern observed by others in rat and mouse although
the guinea pig does not undergo a prepartum progesterone withdrawal. In
animals with a 3-wk lactation period, milk cAMP concentration decreases
approximately 40% between days 10 and 20, whereas the mammary gland level
increases 22% per unit wet tissue weight. Although milk concentrations of
lactose and cAMP are weakly correlated, a strong correlation exists between
the total collected daily outputs of these two substances. The results
suggest that, as lactation proceeds, mammary gland cAMP levels gradually
increase, whereas milk cAMP levels decrease. Concurrently, lactose output
decreases as lactation proceeds. These observations are consistent with
first, a milk secretory route for regulating mammary gland cAMP levels (in
addition to synthesis and hydrolysis), and second, an inhibitory action of
cAMP on lactose synthesis.
