Changes induced by adrenalectomy, triamcinolone treatment and deoxycorticosterone (DOC) treatment on the uptake of [3H]-serotonin into platelets were studied ex vivo, using rat platelets suspended in physiological medium. Adrenalectomy caused a decrease in active uptake of serotonin and an associated increase in apparent Km. Treatment of the adrenalectomized rats with triamcinolone (0.25 mg/kg), but not DOC (1.0 mg/kg) restored the active uptake of serotonin. At triamcinolone dose of 0.5 mg/kg, the serotonin uptake was raised to a level that was significantly higher than normal. Kinetic analysis of uptake data showed the apparent Km to be affected by both triamcinolone and DOC, while the apparent Vmax of uptake rate was increased by triamcinolone treatment.

Male rats were treated with a fixed dose of aminoglutethimide (50 mg/kg s.c.) or with progressively increasing doses (50-100 mg/kg s.c.) for 3 days. Corticosterone levels were found to be decreased in the latter group. Platelet uptake of serotonin as well as the apparent Vmax were decreased, whereas the Km of uptake were increased when compared with that of the control group. Addition of ACTH (10 iu/dl) to control rat platelet and corticosterone (10-80 micrograms/dl) or triamcinolone (0.5-5.0 micrograms/dl) to adrenalectomized rat platelet suspension in vitro did not increase the serotonin uptake of the preparation. Administration of exogenous dexamethasone (0.05-0.2 mg/kg i.m.) or triamcinolone (0.05-5.0 mg/kg i.m.) to adrenalectomized rats, caused a dose related increase in active uptake of serotonin by the platelets. Deoxycorticosterone (0.1-1.0 mg/kg i.m.) did not have this effect. The time course of response to, and the maximum percentage increase in platelet serotonin uptake by, exogenous corticosteroids are related to their glucocorticoid potency. The possible role of glucocorticoids on platelet serotonin uptake process is discussed.