Blunted dexamethasone-induced growth hormone responses in acute mania

Dynamic endocrine testing using a variety of probes has revealed abnormalities of the somatotropic axis in bipolar mania. In health, acute administration of dexamethasone (DEX) results in the secretion of growth hormone (GH) by possibly inhibiting somatostatin tone. We elected to determine DEX/GH responses in acute mania. Eight male bipolar manics were compared with eight age-matched healthy volunteers. Four milligrams of oral DEX was administered at 0900 h (time 0 min) and plasma samples for GH were taken at +60, +180, +240 and +300 min. Baseline samples for GH and cortisol were taken at -15 min and 0 min. Patients had higher basal cortisol levels (391.6 +/- 89.4 nmol/l) as opposed to controls (138.0 +/- 13.2 nmol/l) (paired t-test, t = 4.68, df = 6, p < .0004). The mean (+/- SD) delta GH (calculated as the maximum GH level relative to baseline) in the manic patients was 0.7 +/- 0.8 ng/ml and in the healthy controls was 9.2 +/- 4.3 ng/ml (paired t-test, t = -0.589, df = 6, p < .0001). In conclusion, patients with bipolar mania had lower DEX-induced GH responses in comparison to controls.