Comparison of the renal effects of indoramin and prazosin

Indoramin and prazosin are both potent and selective alpha 1 adrenoceptor antagonists. Indoramin has been reported to decrease baroreceptor sensitivity, whereas prazosin has been reported to increase it. The current studies examined the relative potencies of the two drugs in inhibiting the renal vascular alpha 1 adrenoceptor and also the renal and cardiovascular effects of these agents. The drugs were infused intravenously at rates in which they equally antagonized alpha 1-receptors. Indoramin decreased blood pressure by as much as 29 mm Hg with the doses tested and also significantly (p less than 0.05) reduced heart rate. Sodium, potassium, and water excretion, and glomerular filtration rate (GFR) were unchanged. Prazosin tended to reduce blood pressure, but the 11 mm Hg fall was not statistically significant. Heart rate increased significantly (p less than 0.05). Sodium, potassium, and water excretion decreased, with a return toward control values of urine flow but not sodium excretion with higher doses. The GFR was unchanged. The results of this study indicate that neural and endocrine factors modify direct drug effects and that indoramin and prazosin administered acutely differ in the recruitment of these reflexes.