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ARS Home » Pacific West Area » Dubois, Idaho » Range Sheep Production Efficiency Research » Research » Publications at this Location » Publication #107522
Title: ADIPOSE TISSUE LIPOGENEIC ENZYME ACTIVITY, SERUM IGF-1, AND IGF-BINDING PROTEINS IN THE CALLIPYGE

Author
item RULE, D. - UNIV OF WYOMING
item MOSS, GARY - UNIV OF WYOMING
item Snowder, Gary
item COCKETT, NOELLE - UTATH STATE UNIV

Submitted to: Sheep and Goat Research Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2002
Publication Date: 6/6/2002
Citation: Rule, D.C., Moss, G.E., Snowder, G.D., Cockett, N.E. 2002. Adipose tissue lipogeneic enzyme activity, serum IGF-1, and IGF-binding proteins in the callipyge lamb. Sheep and Goat Research Journal 17:39-46.

Interpretive Summary: This research investigated various biological mechanisms associated with a dominant gene (callipyge) effect that enhances muscle growth and decreases fat in sheep. The specific biological mechanisms causing the reduction in fat were unknown. We investigated several hypotheses which included that enzymes in the fat cells were down regulated by the gene, or that the fat cells were not receiving sufficient substrates from the blood to produce fat. By evaluating the fat cell enzymes we determined that lambs expressing the dominant gene had lower lipid enzyme activity. The cause for decreased lipid enzyme activity remains unknown but we have shown that the fat cell activity is decreased by the callipyge gene. This basic research will contribute significantly to our understanding of the relationship of nutrient partitioning to body composition.

Technical Abstract: The objective was to determine if reduced adipose tissue accretion in callipyge lambs during growth was related to activities of lipogenic enzymes and serum concentrations of insulin, IGF-I, and IGF-binding proteins. Normal lambs and callipyge lambs were slaughtered at 25, 41, 57, or 73 kg, with five normal and five callipyge lambs in each weight group. Subcutaneous, intermuscular, and perirenal adipose tissue samples were dissected after slaughter. Tissue homogenates were assayed for fatty acid synthase, acyl-CoA synthetase, glycerophosphate acyltransferase, and lipoprotein lipase activities. Normal lambs had greater (P < .09) lipogenic enzyme activities than the callipyge lambs. Nearly all numeric values for enzyme activities in adipose tissue depots were higher for normal lambs. Differences in enzyme activity in subcutaneous adipose tissue occurred most often at the heavier weight, whereas in intermuscular adipose tissue, differences occurred most often at the lighter weights. Serum concentrations of insulin were not affected by genotype (P > .2). Serum insulin in fed callipyge lambs was not affected by body weight, but increased with weight in fed normal lambs (P = .03). Two-day fasted lambs had decreased serum insulin in both genotypes, which increased (P = .03) similarly with body weight for both genotypes. Serum IGF-I was greater (P = .09) in normal lambs at 73 kg, whereas IGF-I in 2-d fasted callipyge lambs was greater (P = .03) than normal lambs. No genotype effects were observed for the relative proportions of the IGF-binding proteins. Overall, callipyge lambs have lower lipogenic enzyme activities in adipose tissue than normal lambs, but that these changes were not related to serum concentrations of insulin or IGF-I.