Secretory patterns and metabolic clearance rate of porcine growth hormone in swine selected for growth.

Eleven Landrace pigs (six boars and five gilts, 50 kg) representing lines selected for three generations for maximum weight at 200 d of age were compared to eight pigs (four boars and four gilts, 50 kg) representing contemporary randomly selected Landrace controls to determine the effect of selection for growth on the metabolic clearance rate (MCR) and plasma concentrations of porcine growth hormone (GH). To estimate MCR of GH, the disappearance of a bolus of porcine GH was monitored over 120 min following its i.v. injection. Blood samples also were collected every 15 min over a 6-h period before injecting GH to determine baseline and overall mean GH concentrations, mean peak amplitude and number of GH secretory episodes. Boars exhibited greater overall mean GH concentrations (4.80 vs 3.11 ng/ml; P less than .05) and had greater maximum GH concentrations associated with secretory episodes (16.11 vs 10.80 ng/ml; P less than .05) than did gilts. There were no differences between boars and pigs exhibited greater baseline GH concentrations (2.04 vs 1.25 ng/ml; P less than .01) than did those from the unselected Landrace line. Selected and control pigs exhibited similar (P greater than .15) overall mean concentrations of GH, frequency of secretory episodes, amplitude of GH peaks and MCR. These data demonstrate that pigs selected for heavier weight at 200 d of age had greater basal plasma GH concentrations than did unselected control pigs.