Lack of direct action of α-human atrial natriuretic polypeptide on the in vitro perfused segments of Henle's loop isolated from rabbit kidney

We examined direct effects of -human atrial natriuretic polypeptide (-hANP) on water and NaCl transport across the segments of Henle's loop by the in vitro microperfusion technique. In the medullary and the cortical thick ascending limb, 10^–6 M -hANP did not affect the transmural voltage (V_t) and the lumen to bath³⁶Cl flux whether it was added to the perfusate or to the bath. In the thin ascending limb, 10^–6 M -hANP did not affect the lumen to bath³⁶Cl flux. The peptide may not affect permselectivity of the thin ascending limb, since it did not influence the diffusion potential generated in the presence of a NaCl gradient. In the descending limb, 10^–6 M -hANP did not affect osmotic water permeability, whether it was added to the perfusate or to the bathing fluid. From these observations, we conclude that -hANP does not show direct effects on water and NaCl transport in the segments of Henle's loop at least under our experimental conditions. Therefore, natriuresis by -hANP may be caused either by an action on nephron segments other than Henle's loop or by an action on renal vasculatures.