Effect of glucocorticoids on renal dopamine production

This study assess the effects of glucocorticoids on dopamine excretion and evaluates the participation of renal dopamine in the effects of glucocortic oids on renal function and Na+ excretion. Dexamethasone (i.m.; 0.5 mg/kg) w as administered to male Wistar rats on day 2 or on days 2 and 5. Daily urin ary excretions of Na+, dihydroxyphenylalanine (DOPA), dopamine and dihydrox yphenylacetic acid were determined from day 1 to day 7. Renal function was evaluated 8 h after dexamethasone administration in a separate group. The f irst dose of dexamethasone increased about 100% diuresis and natriuresis, i ncreased urinary DOPA and renal plasma flow, and did not affect urinary dop amine or the other parameters evaluated. These effects were not affected by previous administration of haloperidol. The second dexamethasone dose incr eased about 200% diuresis and natriuresis, increased urinary dopamine, DOPA , dihydroxyphenylacetic acid, U-osm X V and both glomerular filtration rate and renal plasma flow. Carbidopa administered before the second dexamethas one dose blunted both the diuretic and the natriuretic response whereas hal operidol abolished or blunted all the effects of the second dexamethasone d ose. These results show that modifications in renal dopamine production pro duced by corticoids may contribute to the effects of these hormones on Nabalance and diuresis and suggest that regardless the factor that promotes a n increase in renal perfusion and glomerular filtration rate during long te rm administration of glucocorticoids, a dopaminergic mechanism is actively involved in the maintenance of these hemodynamic changes. (C) 1999 Elsevier Science B.V. All rights reserved.