Changes in bovine mammary insulin binding during pregnancy and lactation

1. Binding of insulin to microsomes from mammary glands of pregnant and lactating dairy cows was characterized. 2. Binding affinities of the insulin receptor did not change from pregnancy to lactation. 3. Maximal specific binding occurred in microsomes from cows in mid-pregnancy and declined in microsomes from cows in late pregnancy. 4. Insulin binding continued to decrease from early to mid-lactation and increased during late lactation. 5. Results indicate that decreased sensitivity in mammary tissue from lactating dairy cows is at least in part a result of a reduction in insulin receptor number. 6. Results demonstrate further physiological differences between the ruminant and non-ruminant mammary gland.