Increase in Pulsatile Secretion of Growth Hormone during Failure of Catch-Up Growth following Glucocorticoid-Induced Growth Inhibition 1

Abstract

The pattern of growth hormone (GH) secretion was determined in rats injected with cortisone acetate, 5 mg/rat/day subcutaneously, or with an equivalent volume of saline for 4 days from age 40 days. Cortisone injections resulted in inhibition of growth of body weight and tail length. During recovery the rats resumed a normal rate of growth but failed to show catch-up growth acceleration. From 17 to 27 days of recovery, plasma was sampled at 15-min intervals through the lights-on period, 06:00 to 18:00, via a catheter chronically implanted in the superior vena cava. During sampling each rat was housed singly in an insulated chamber, unrestrained, and with food and water ad lib.Cortisone-treated animals had a normal periodicity of GH plasma concentration, but they showed a reduction in values in the range of 50 to 99 ng/ml (P0.01) and an increase of values in the range of 200 to 499 ng/ml (P0.025) and above 1000 ng/ml (P 0.05). The area under the GH concentration curve of the cortisone-treated rats was significantly greater than that of the controls, 100.9 ± 18.7 (mean ± SE) units vs 55.3 ± 7.4 (P0.025). Thus, increased growth hormone secretion during the light phase persisted in spite of failure of catch-up growth acceleration. The findings indicate that the mechanism involved in GH release is linked to the catch-up growth control.