Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 8/1/1997
Publication Date: N/A
Technical Abstract: A leptin cDNA was recently cloned from adipose tissue of humans, rodents, and livestock. In rodents, percentage body fat is positively correlated to mRNA levels of leptin and negatively correlated to feed intake. Two compounds known to influence feed intake and fat content of a carcass in ruminants are zeranol (Z;an estrogenic growth promotant) and recombinant growth hormone (GH). The objective of these studies was to determine the effect of Z and GH on steady-state mRNA levels of leptin and the GH receptor (GHR) in adipose tissue of growing wethers. In two studies, 36 whiteface wethers weighing 45.8 +/ 3 kg were assigned randomly to a control group (CT1; n=8), a group implanted with 12 mg of zeranol (Z, n=12); Ralgro, Mallinckrodt Vet.), a second control group (CT2; n=8) or a group injected with 120 mg of bovine GH (n=8; Posilac, Monsanto Co.). Two wk after treatment, subcutaneous fat was biopsied from CT1, CT2, Z and GH treated wethers. Weight gain was similar in Z and GH treated wethers relative to CT1 and CT2 treated wethers in both experiments [P = .7 and .9, (Z) 1.7 +/ .6 = (CT1) 1.4 +/ .3 and (GH) 1.7 +/ .7 = (CT2) 1.7 +/ .6 kg per 2 wk]. Treatment of wethers with Z resulted in a decrease in relative mRNA levels of leptin and GHR [(Z) .75 +/ .1 < (CT1) 1.5 +/ .2 and (Z) 1.0 +/ .2 < (CT2) 5.5 +/ 1.4], whereas GH tended to increase (P < .1) the relative levels of these transcripts [(GH) 2.1 +/ .6 > (CT1) 1.2 +/ .2 and (GH) 6.9 +/ 2.4 > (CT2) 2.9 +/ .5] when compared to control treated wethers. These data provided evidence that compounds known to influence feed intake and lean growth in ruminants differentially influence responsiveness and signalling mechanisms of adipose tissue.