Lipid synthesis by co-cultures of mammary, liver, and adipose tissue explants from sometribove (recombinant methionyl bovine somatotropin)-treated dairy cows.

Bovine somatotropin was given to six lactating (230 day) cows (40 mg/day X 5-days) and excipient was given to six control cows. Mammary, liver, and adipose explants from somatotrophin and control cows were co-cultured at 37 degrees C for 24 h with 0.5 microCi [14C]acetate/ml media with or without 0.5 micrograms/ml somatotrophin. Tissue lipids were extracted with chloroform/methanol and separated by thin layer chromatography. In vivo somatotrophin increased milk production 2.4 kg/day compared to a 0.9 kg/day decrease by controls. Mammary tissue from somatotrophin cows incorporated more [14C]acetate into total lipids (4417 vs. 3016 dpm/mg tissue) than controls. Adding somatotrophin to explant cultures from somatotrophin cows further increased incorporation into total lipids (4839 vs. 3994 dpm/mg tissue). In contrast, adipose tissue from somatotrophin cows incorporated less [14C]acetate into total lipids than controls (1524 vs. 2581 dpm/mg tissue). Serum IGF-I concentration correlated well (r = 0.69) with milk output differences between Days 1 and 5 of treatment. Media IGF-I concentration correlated well (r = 0.61) with the difference in total lipid synthesis between the in vitro control and somatotrophin groups. Results support the concept that somatotrophin increases milk production by partitioning nutrients away from adipose toward mammary tissue.