EFFECTS OF ATRIAL-NATRIURETIC-PEPTIDE AND VASOPRESSIN ON CHLORIDE TRANSPORT IN LONG-LOOPED AND SHORT-LOOPED MEDULLARY THICK ASCENDING LIMBS

Recent studies have suggested a selective effect of atrial natriuretic peptide (ANP) in regulating NaCl reabsorption in juxta-medullary nephrons. We examined (a) functional differences between medullary thick ascending limbs from long and short loops of Henle (lMAL and sMAL, respectively) and (b) the interaction of ANP and arginine vasopressin (AVP) on Cl- transport (J(Cl)) in these two segments. AVP-, glucagon-, and calcitonin-stimulated cAMP accumulation was higher in lMAL. than in sMAL. 10(-10) M AVP increased J(Cl) in lMAL but not in sMAL. ANP-stimulated cGMP production was higher in lMAL than in sMAL. 10(-10) and 10(-8) M ANP inhibited AVP-stimulated J(Cl) in lMAL by 26-30% (from 70.3+/-11.4 to 51.7+/-13.6 pmol/mm per min and from 88.1+/-10.1 to 61.8+/-11.7 pmol/mm per min, respectively), and this effect was mimicked by 10(-5) to 10(-4) M cGMP. This effect of ANP in lMAL could account for a large part of the ANP-induced natriuresis and diuresis in vivo, in that the rate of NaCl reabsorption in MAL is the largest among distal nephron segments, providing the chemical potential energy for the renal countercurrent multiplication system.