Humoral and renal effects of ibopamine in normal subjects

The acute effects of 50 mg of ibopamine (SB-7505), the 3,4-diisobutyryl ester of N-methyldopamine, were investigated after oral administration to 10 adult subjects without evidence of renal, hepatic or cardiovascular disease. Blood pressure and heart rate did not change while diuresis and urinary electrolyte excretion increased significantly during the 240 min of the study. Glomerular filtration rate (GFR) was also increased at 80 min after ibopamine, whereas plasma aldosterone and prolactin were slightly decreased. In contrast to dopamine, ibopamine did not stimulate plasma renin activity. These results are attributable to the ability of ibopamine to be rapidly deesterified to N-methyldopamine (epinine) which has been previously shown to exert peripheral effects similar to those of dopamine. Therefore, the increased GFR can be ascribed to an enhanced renal blood flow. On the contrary, taking into account the significant increase of the fractional excretion of sodium (FeNa) the rise in sodium excretion seems to be the consequence of a direct tubular effect of epinine, even though the slight decrease in peripheral aldosterone concentration would have been a contributing factor. Urinary flow rate might be enhanced by the high sodium delivery to the distal nephron, rather than by a postulated dopaminergic inhibition of arginine-vasopressin release.