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Growth hormone stimulation of serum insulin concentration in cattle: Nutritional dependency and potential mechanisms
Authors:J. Feng  Z. Gu  M. Wu  F.C. Gwazdauskas  H. Jiang
Affiliation:1. College of Animal Science, Zhejiang University, Hangzhou, China;2. Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA;3. Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
Abstract:
Previous studies on the effect of growth hormone (GH) on serum insulin concentration in cattle had generated seemingly conflicting results, and little was known about the mechanism by which GH affects serum insulin concentration in cattle, if it does. In this study, we determined whether the effect of GH on serum insulin concentration in cattle could be affected by the nutritional levels of the animal and whether GH increased serum insulin concentration in cattle by directly stimulating insulin release or insulin gene expression in the pancreatic islets. Administration of recombinant bovine GH increased serum insulin concentration in nonlactating, nonpregnant beef cows fed a daily concentrate meal in addition to ad libitum hay, but it had no effect in those cows fed hay only. Both GH treatments for 1 and 24 h increased insulin concentrations in cultures of pancreatic islets isolated from growing cattle. Growth hormone treatment for 24 h increased insulin mRNA expression in cultured bovine pancreatic islets. Growth hormone treatment for 16 h increased reporter gene expression directed by a ∼1,500-bp bovine insulin gene promoter in a rat insulin-producing β cell line. Taken together, these results suggest that exogenous GH can increase serum insulin concentration in cattle, but this effect depends on the nutritional levels of fed cattle, and that GH increases serum insulin concentration in cattle by stimulating both insulin release and insulin gene expression in the pancreatic islets.
Keywords:Growth hormone   Insulin   Pancreas   Cattle   Feeding levels
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