BICARBONATE TRANSPORT ALONG THE LOOP OF HENLE .2. EFFECTS OF ACID-BASE, DIETARY, AND NEUROHUMORAL DETERMINANTS

The loop of Henle contributes to renal acidification by reabsorbing about 15% of filtered bicarbonate. To study the effects on loop of Henle bicarbonate transport (JHCO(3)) of acid-base disturbances and of several factors known to modulate sodium transport, these in vivo microperfusion studies li;ere carried out in rats during: (a) acute and chronic metabolic acidosis, (b) acute and chronic (hypokalemic) metabolic alkalosis, (c) a control sodium diet, (d) a high-sodium diet, (e) angiotensin II (AII) intravenous infusion, (f) simultaneously intravenous infusion of both AII and the ATI receptor antagonist DuP 753, (g) acute ipsilateral mechanico-chemical renal denervation. Acute and chronic metabolic acidosis increased JHCO(3); acute metabolic alkalosis significantly reduced JHCO(3), whereas chronic hypokalemic alkalosis did not alter JHCO(3). Bicarbonate transport increased in animals on a high-sodium intake and following AII administration, and the latter was inhibited by the AII (AT(1)) receptor antagonist DuP 753; acute renal denervation lowered bicarbonate transport. These data indicate that bicarbonate reabsorption along the loop of Henle in vivo is closely linked to systemic acid-base status and to several factors known to modulate sodium transport.