EFFECTS OF CYSTEAMINE ON PULSATILE GROWTH-HORMONE RELEASE AND PLASMA-INSULIN CONCENTRATIONS IN SHEEP

The effects of cysteamine (CSH; 0, 50, or 100 mg/kg BW), a somatostati n depleting agent, on growth hormone (GH) and insulin (INS) secretion were studied in sheep (Ovis aries), Cysteamine was administered as a s ingle intragastric bolus on day 0 (0900), Jugular blood samples were c ollected at 15-min (GH) and 2-hr (INS) intervals over an 8-hr period ( 1100-1900) on day 0, 3, and 7, Intragastric administration of CSH at 5 0 mg/kg BW augmented (quadratic, P = .04) mean plasma GH concentration , with the greatest response occurring on day 3, Baseline GH concentra tions were elevated in wethers dosed with 50 mg/kg BW CSH on day 3, wh ereas wethers dosed with 100 mg/kg BW CSH had lower baseline GH concen trations on day 0 (CSH x day interaction, P = .02). Cysteamine adminis tration increased GH pulse amplitude (quadratic, P = .15), with the gr eatest magnitude of change occurring with 50 mg/kg BW CSH on day 0 and 3, Frequency of GH pulses was increased (quadratic, P = .10) followin g CSH treatment, Administration of 100 mg/kg BW CSH augmented plasma I NS on day 0 (CSH x day interaction, P = .09), These findings indicate that CSH alters GH and INS secretion in a dose-dependent and temporal manner, The observed changes in mean and baseline plasma GH concentrat ions associated with 50 mg/kg BW CSH are consistent with somatostatin depletion; however, higher doses of CSH appear to disrupt GH secretion by an alternative mechanism.