Plasma growth hormone (GH) and somatomedin C response to continuous growth hormone-releasing factor (GRF) infusion in patients with GH deficiency

Pituitary growth hormone (GH) responses during a 10-h iv infusion of saline or human GH-releasing factor (hGRF-44) at 500 ng/kg/h, followed by an iv bolus injection of hGRF-44 at 2 μg/kg body weight, were studied in 10 patients with GH deficiency. During saline infusion in 4 patients, small plasma GH increase were observed in 2 patients. However, during hGRF infusion in 6 patients, up to 4 or 13 pulses of GH secretion were observed. The mean integrated GH pulse area during hGRF infusion was 22.5 ± 5.2 (se) ng/ml × h, which was greater than that obtained during saline infusion. Plasma somatomedin C levels did not increase after hGRF infusion. After saline or hGRF infusion all patients responded to an iv bolus injection of the peptide. These results indicate that hGRF infusion augments GH secretion by increasing the number and amplitude of GH pulses and that the infusion does not cause pituitary somatotrophs to lose their capacity to respond to hGRF subsequently.