Pulsatility of plasma growth hormone and hepatic growth hormone receptor characteristics of broiler chickens divergently selected for abdominal fat content.

1. Plasma growth hormone (GH) pulsatility and hepatic GH receptor characteristics were compared in experimental lines of meat-type chickens selected for high (HF) or low (LF) abdominal fat content. 2. Mean GH concentration, baseline and amplitude of pulses were slightly, but not significantly, greater in LF chickens. Length and frequency of pulses were similar. 3. LF chickens exhibited higher plasma triiodothyronine (T3) concentrations. This difference between genotypes disappeared when the diet was supplemented with 1 mg/kg T3. 4. Specific binding of GH to liver membranes was higher for the fat line but was depressed by T3 supplementation to the same level in both lines. No difference was observed between lines for affinity constants. 5. It is concluded that direct selection for leanness has a less pronounced, if any, effect on GH pulsatility as compared with selection for food conversion efficiency; therefore, different physiological mechanisms are triggered to achieve leanness.