The present study was designed to characterize the developmental changes in the renal responses to dopamine DA1-receptor activation in chronically instrumented preterm (109-115 days) and near-term (130-140 days, full term 145 days) fetal sheep. Cumulative doses of the selective DA1-agonist fenoldopam increased mean arterial blood pressure (MABP) in both preterm (+16 +/- 3%) and near-term fetuses (+16 +/- 3%) but had no significant effect on renal blood flow velocity. Infusion of the DA1-antagonist SCH-23390 did not affect the increase in MABP, suggesting that the effect of fenoldopam on MABP was not directly related to activation of DA1-receptors. Fenoldopam infusion had no significant effects on renal function parameters in preterm fetuses. In near-term fetuses, however, fenoldopam increased urinary flow rate (82.6 +/- 20.9%, P < 0.003), glomerular filtration rate (GFR; 16.6 +/- 4.9%, P < 0.01), urinary sodium excretion (40.1 +/- 14.9%, P < 0.02), and fractional excretion of sodium (26.8 +/- 11.2%, P < 0.03). Infusion of the DA1-antagonist SCH-23390 blocked the fenoldopam-induced diuresis and natriuresis but had no significant effect on the rise in GFR. Fenoldopam infusion had no significant effects on plasma renin activity and plasma aldosterone concentration and on urinary prostaglandin (PG) excretion (PGE2, PGF2 alpha, and 6-keto-PGF1 alpha). Taken together, these results suggest that the renal effect of DA1-receptor activation is age dependent and that stimulation of DA1-receptor in near-term fetuses is associated with a diuresis and natriuresis that seem to be independent of renal hemodynamics and adrenal effects.