LOSS OF THE DIURNAL-VARIATION OF PYRIDOSTIGMINE-INDUCED GROWTH-HORMONE RESPONSES IN DEPRESSION - THE EFFECT OF CORTISOL

Growth hormone (GH) plasma concentrations reflect a balance between st imulation via GH-releasing hormone and inhibition by somatostatin. Cho linergic agonists enhance GH release by inhibiting somatostatin secret ion and in health, stimulated GH release undergoes diurnal variation. We investigated the influence of cortisol on pyridostigmine-induced GH responses by testing six: patients with DSM-III-R major depression at 09.00 and 14.00 h. There were no differences in GH responses to pyrid ostigmine between 09.00 and 14.00 h despite a preservation of the circ adian variation of cortisol levels. If cortisol plays an important rol e in regulating cholinergic activity one would expect the diurnal vari ation of pyridostigmine-induced GH release to be preserved. As it is n ot, a reasonable assumption to make is that the muscarinic supersensit ivity observed in depression may be independent of the prevailing ster oid milieu.