Insulin regulates circulating insulin-like growth factors and some
of their binding proteins in lactating cows .
McGuire, Mark A., Debra A. Dwyer, Robert J. Harrell, and Dale E.
Bauman.
Department of Animal Sciences, Cornell University, Ithaca, NY
14853
APStracts 2:0115E, 1995.
Four lactating Holstein cows were subjected to a hyperinsulinemic
-euglycemic clamp to evaluate the effects of insulin on circulating
concentrations of insulin-like growth factors (IGF) and their binding
proteins (IGFBP). Baseline blood samples were taken every 4 h for 2
d. For the 4-d clamp, insulin was infused (1 ?[mu]g/(kg ?body wt_h))
into the jugular vein and exogenous glucose infused to maintain
euglycemia. Circulating insulin was increased approximately 5-fold,
while glucose was maintained within 10% of baseline concentrations by
infusion of 0.15 ?g/(kg body wt_h) glucose. Hyperinsulinemia
-euglycemia approximately doubled IGF-I (145 vs 286 ng/ml, SE=20)
while decreasing circulating IGF-II (286 vs 180 ng/ml, SE=32).
Densitometry of Western blots demonstrated no change in IGFBP-3 or a
30,000 Mr band during the clamp. However, IGFBP-2 decreased 73% and a
26,000 Mr band decreased 58% by the end of the clamp. Therefore,
insulin directly or via secondary changes, increased circulating
concentrations of IGF-I while decreasing concentrations of IGF-II,
IGFBP-2 and a 26,000 Mr IGFBP in lactating cows.
Received 28 November 1994; accepted in final form 15 May 1995.
APS Manuscript Number E491-4.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 26 May 1995.