RESUMO
The effects of sodium orthovanadate, angiotensin II (A II) and noradrenaline (NA) were studied on the isolated perfused rat kidney (IPRK) and on the diameter of the glomerular capsule and tuft. Vanadate (4.5 microM), A II (20 nM) and NA (17.3 microM) increased the total resistance of the IPRK. There was a simultaneous increase in glomerular filtration rate with vanadate and A II, but a decrease with NA. The glomerular tuft/capsule diameter ratio decreased significantly from 0.85 (control) to 0.81, 0.81 and 0.78 for vanadate, A II, and NE treated kidneys, respectively. The decrease in ratio was associated with an increase in diameter of the glomerular capsule for A II and NE. This finding accompanied with simultaneous rise in TPR and GFR in the case of vanadate and A II, indicates that the post capillary efferent arteriolar vasoconstriction is a component in the mechanism of action with A II and vanadate. Evidence for such a component is less clear for NA because GFR decreases and TPR increases. Vanadate may affect both with a predominance on the efferent arteriole. The data indicate that histological measurements of glomerular size lead to a better understanding of the mechanisms of vasoactive drugs acting on the kidney.