Effect of bovine growth hormone on incorporation of [14C]acetate into lipids by co-cultures of bovine mammary, liver, and adipose tissue explants.

Incorporation of [14C]acetate into lipids was measured in 24 hr co-cultures of mammary, liver and adipose tissue from Holstein cows at 53, 210 and 318 d of lactation in the presence or absence of bovine growth hormone. Little (less than 1%) of the labeled lipids appeared in the media relative to that incorporated into the tissue. In mammary tissue, incorporation of [14C]acetate was highest into triglycerides (16,298 cpm/mg mammary tissue), followed by phospholipids (1,887 cpm), free fatty acids (1,252 cpm), diglycerides (708 cpm), free cholesterol (360 cpm) and monoglycerides (93 cpm). Bovine growth hormone did not increase incorporation of [14C]acetate when mammary or adipose tissue were incubated separately. However, in the presence of liver and adipose tissue, bovine growth hormone significantly increased the incorporation of [14C]acetate into triglycerides, diglycerides, free fatty acids and free cholesterol by mammary tissue. These results suggest that bovine growth hormone acts on mammary tissue indirectly through liver and adipose tissue to increase lipid synthesis. This mechanism may play a role in the action of bovine growth hormone in vivo to increase milk and milk fat production.