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

We examined direct effects of alpha-human atrial natriuretic polypeptide (alpha-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 alpha-hANP did not affect the transmural voltage (Vt) and the lumen to bath 36Cl flux whether it was added to the perfusate or to the bath. In the thin ascending limb, 10(-6) M alpha-hANP did not affect the lumen to bath 36Cl 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 alpha-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 alpha-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 alpha-hANP may be caused either by an action on nephron segments other than Henle's loop or by an action on renal vasculatures.