Effect of Size and Lipid Composition of Mammary Gland Fat-Pad on Mammary Gland Growth1,2

Abstract

Pregnant rats pair-fed diets containing either 30% corn oil or 30% coconut oil had mammary fat-pads which differed significantly in every fatty acid except 16:0 and 18:1. The corn oil diet produced adipose tissue with slightly more than 30% saturated fatty acids whereas the coconut oil diet resulted in over 60% saturated fatty acids. However, at 20 days of pregnancy, mammary gland total deoxyribonucleic acid, total ribonucleic acid, and ribonucleic acid/deoxyribonucleic acid ratio were not significantly different among groups of rats with different mammary fat-pad fatty acid compositions. In comparison to the contralateral side, or to animals receiving saline, the injection of 2 units of insulin into the right fat-pad for 14 days prior to mating had no significant effect on mammary gland nucleic acids on the 20th day of pregnancy. However, when insulin was continued throughout pregnancy, deoxyribonucleic acid and ribonucleic acid were highly significantly increased over the saline-injected left side. Autoradiographic studies showed that the increase in deoxyribonucleic acid in response to insulin during pregnancy was not due to a stimulation of deoxyribonucleic acid synthesis in connective tissue cells.