|Carroll, Jeffery - Jeff Carroll|
|Mc Arthur, N|
Submitted to: American Society of Animal Science Southern Section Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 1/27/2001
Publication Date: N/A
Technical Abstract: Whether genotype influences somatotrophic gene expression and function in 3/4 Angus or Brahman steers was evaluated. Growth rate, somatotroph number, anterior pituitary content of growth hormone (GH) mRNA, liver content of GH receptor and IGF-I mRNA, and plasma GH and IGF-I levels in slaughter weight 3/4 Angus (A; n=47) and 3/4 Brahman (B; n=40) steers were evaluated. Steers were produced by embryo transfer as a series of double reciprocal backcrosses and F2 full-sibling families from purebred Angus, purebred Brahman, and F1 parents, and slaughtered at a target weight of 500 kg. Pituitary and liver tissues were collected for immunocytochemistry and mRNA analysis, and blood was collected for GH and IGF-I RIA. Tissues were homogenized and total RNA extracted. GH mRNA expression in the anterior pituitary, and GHR and IGF-I mRNA expression in the liver were determined via ribonuclease protection assays and quantified via integrated optical density units. There was no difference for ADG from birth to weaning or weaning to finish. The A steers had increased anterior pituitary weight (P<.0001; 1.39 +/ .04 vs 1.05 +/ .03 g; A vs B); however, B steers had increased GH cell number/mm**2 (P<.008; 1600.1 +/ 54.0 vs 1865.2 +/ 84.5; A vs B). There was no difference in GH mRNA expression; however, GHR mRNA expression tended to be higher in B steers (P<.09; .76 +/ .09 vs 1.06 +/ .15; A vs B). Plasma GH was not different. The B steers had higher liver IGF-I mRNA expression (P<.04; .06 +/ .01 vs. 11 + .02; A vs B); however, there was no difference in plasma IGF-I. These results suggest increased liver responsiveness to GH in B cattle due to increased GHR expression in the liver which resulted in increased IGF-I mRNA in the liver.