Date of Award
Doctor of Philosophy
Binding of ('125)I bovine insulin and ('125)I bovine growth hormone (bGH) to mononuclear cells isolated from blood and plasma membranes isolated from liver, kidney and fat was characterized in both rats and cattle. In both rats and cattle, insulin and GH receptors exhibited specificity and high affinity (Ka(,1) 5 to 10 x 10('8) M('-1) and Ka(,2) 2 to 20 x 10('7) M('-1)). Bovine mononuclear cells had approximately 3,700 high affinity and 15,000 low affinity sites for insulin per cell. All bovine tissue membranes examined exhibited similar insulin binding characteristics, but maximum binding percentage was 1/3 that of rat tissues. Membranes isolated from rat liver and adipose tissue bound similar amounts of insulin, while membranes from kidney bound only 1/10 of that by liver and adipose. GH did not bind specifically to cattle mononuclear cells. GH binding to liver membranes of rats and cattle was similar. Rat kidney membranes specifically bound GH, but specific binding of bGH could not be demonstrated in bovine kidney. This study indicates bovine insulin and GH receptors are physically similar to those in rats, but major organ differences exist, especially in the kidney. Binding of insulin and bGH was also characterized in tissues from large and small framed cattle to determine if modulation of receptors plays a role in regulating hormone action. Mononuclear cells isolated from small framed cattle had lower binding capacity than did cells isolated from large framed cattle, but this difference was small compared with the higher concentrations of plasma insulin observed in the small cattle. These differences in insulin receptors on mononuclear cells were not associated with parallel changes in liver and kidney membrane receptors. There was no difference in amount of bGH bound to liver membranes of large and small framed cattle. These studies suggest insulin and bGH receptors play a relatively minor role in modifying hormone action in cattle growth and metabolism.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Steven Lynn Nissen
Nissen, Steven Lynn, "Characterization of insulin and growth hormone receptors in bovine tissues " (1981). Retrospective Theses and Dissertations. 6842.