[Lack of effect of the administration of TRH on growth hormone secretion induced by dexamethasone]

The usually accepted effect of corticosteroids on growth hormone secretion (GH) is the reduction or blockage of secretion. Our laboratory has previously reported that corticosteroids could have an acute stimulatory effect on this secretion; we have now studied the effect of administering THR on corticosteroids induced GH secretion. Three stimulatory tests were performed to three healthy volunteers on different days. Saline administration on time 0 and time 120 minutes (control test) did not modify GH levels. On the contrary, the administration of 4 mg Dexamethasone i.v. on time 0 induced an increase in GH with a maximum peak of 10 = 3.3 micrograms/L after three hours being these differences statistically significant (p less than 0.05) when referred to the control test from 120 to 240 minutes. The corticosteroid GH stimulus presented a peculiar secretion pattern: During two hours there were no changes in basal values and afterwards the values were maintained in maximum peak values during two hours, with a great net release of GH. The administration of THR (400 micrograms iv) 120 minutes after the administration of Dexamethasone did not notify GH secretion pattern when compared with the group receiving only Dexamethasone. To conclude, the administration of corticosteroids is a new and peculiar stimulus for GH secretion. Lack of THR inhibitory function suggests that the corticosteroid stimulatory function is probably at the hypothalamus level.