Adrenergic control of bicarbonate absorption in the proximal convoluted tubule of the rat kidney

Abstract

The effects of norepinephrine and phenoxybenzamine on bicarbonate absorption in the rat proximal convoluted tubule were studied by simultaneous microperfusion of tubule and peritubular capillaries. Bicarbonate was determined by using a pH-sensitive membrane electrode system. The rates of bicarbonate absorption$(J_{HCO_3 } )$ were examined in the same proximal tubule before and after the addition of norepinephrine or phenoxybenzamine. When the proximal tubule was perfused with Ringer solution and peritubular capillaries were perfused with albumin Ringer solution,$J_{HCO_3 }$ was 145±3.3 pEq/min×mm. Addition of 2×10⁻⁶ mol/l norepinephrine to the capillary perfusate caused a 21% increase in$J_{HCO_3 }$. Addition of 2×10⁻⁶ mol/l phenoxybenzamine to the capillary perfusate caused a 12% decrease in$J_{HCO_3 }$. Addition of both norepinephrine and phenoxybenzamine to the capillary perfusate caused a 19% decrease in$J_{HCO_3 }$. However, there was no significant effect on$J_{HCO_3 }$ observed when either norepinephrine or phenoxybenzamine was added to the luminal perfusate. These results suggest that adrenergic nerves participate in the regulation of renal tubular bicarbonate absorption through the direct action of norepinephrine on adrenergic receptors located at the basolateral side of the proximal tubule.