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Nutrient Utilization and Protein Turnover in the Hindlimb of Cattle Treated with Bovine Somatotropin^1,2,

Department of Animal Science, Cornell University, Ithaca, NY 14853

Our objectives were to assess the effects of chronic administration of recombinant bovine somatotropin (bST) on nutrient utilization and protein turnover in the hindlimb of growing Holstein steers. External iliac vessels were catheterized to allow for hindlimb measurements of arteriovenous differences and blood flow. Animals were used in a single-reversal design with 16-d treatment periods of daily intramuscular injection of either excipient or 120 µg/kg body wt of bST. On d 11 and 13 of each period, a primed-continuous infusion of L-[sidechain-2,3-³H]tyrosine was initiated, followed by a 4-h sampling period to assess hindlimb nutrient utilization and protein kinetics. Somatotropin did not alter blood flow or the consumption of acetate and oxygen across the hindlimb. In contrast, glucose uptake was reduced by 22% despite increases in arterial concentrations of glucose and insulin of 10 and 114%, respectively. Treatment with bST increased hindlimb protein accretion (estimated from net uptake of tyrosine) and whole-body N balance, each by -40%. A modest increase (10%) in the absolute rate of protein synthesis seemed to account for the improved N retention in the hindlimb with no change in the rate of protein degradation. Thus, bST reduced the responses of the hindlimb to insulin, and a small alteration in protein synthesis was sufficient to explain substantial improvement in protein deposition.

KEY WORDS: • somatotropin • muscle metabolism • growing cattle • protein synthesis

¹ Supported in part by Cornell University Agricultural Experiment Station. Y. R. Boisclair was a recipient of scholarships from the Natural Sciences and Research Council of Canada and Purina Mills, Inc.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ Current address: Molecular, Cellular and Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Building 10, Room 8D14, Bethesda, MD 20892.

⁴ To whom correspondence and reprint requests should be addressed.

⁵ Current address: Victorian Institute of Animal Science, Werribee, Victoria 3030, Australia.

Manuscript received 11 June 1993. Revision accepted 30 November 1993.

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