Effect of Somatotropin and Insulin-Like Growth Factor-I on Milk Lipid and Protein Synthesis In Vitro

¹ Agricultural Research Service, USDA, Beltsville, MD20705
² Agricultural Research Council, Irene Animal Production Institute, Irene 1675, Republic of South Africa
³ Agricultural Research Service, USDA, Wyndmoor, PA 19038

The objective of this research was to test the hypothesis that bST stimulates milk secretion through the action of IGF-I. Cocultures of bovine mammary, adipose, and liver tissues were incubated with increasing concentrations (0 to 1000 ng/ml) of bST, IGF-I, prolactin, or bST plus prolactin. In addition, cocultures of mammary and adipose tissues without liver tissue were incubated with IGF-I. The synthesis of milk lipids and proteins and the concentration of cellular DNA were measured. The addition of liver tissue depressed DNA concentration and the synthesis of lipids and proteins in mammary tissue. In mammary tissue, increasing bST concentration resulted in greater synthesis of FFA, total lipids, and proteins than that produced by increasing concentrations of IGF-I, and the effect on protein synthesis was linear. Conversely, in adipose tissue, increasing the concentration of IGF-I in the presence of liver resulted in greater synthesis of FFA than that obtained by bST, and the effect was linear. The results do not support the hypothesis that bST acts through the actions of IGF-I on mammary cells. Rather, bST alters the delivery of nutrients to the mammary cells from other tissues and affects milk component synthesis through a mechanism that may not involve IGF-I.

Key Words: insulin-like growth factor-I • bovine somatotropin • milk protein • deoxyribonucleic acid

Submitted on October 16, 1995
Accepted on May 10, 1996

This article has been cited by other articles:

				T. D. ETHERTON and D. E. BAUMAN Biology of Somatotropin in Growth and Lactation of Domestic Animals Physiol Rev, July 1, 1998; 78(3): 745 - 761. [Abstract] [Full Text] [PDF]