Effects of insulin and atrial natriuretic peptide on renal tubular sodium handling in sickle cell disease

We assessed the effect of insulin and atrial natriuretic peptide (ANP) on r enal sodium handling in eight patients with sickle cell disease (SCD), who are characterized by loss of vasa recta and long loops of Henle, and matche d control subjects. During insulin infusion (50 mU.kg(-1).h(-1)), fractiona l sodium excretion decreased by 0.44 +/- 0.72% (P = 0.13) in patients with SCD and by 0.57 +/- 0.34% (P = 0.002) in control;subjects, whereas fraction al distal sodium reabsorption increased by 4.1 +/- 1.5% (P < 0.001) and 3.0 +/- 1.5% (P <: 0.001), respectively. Low-dose (0.3 pmol.kg(-1).h(-1)) ANP infusion did not affect renal sodium handling in patients with SCD but incr eased fractional sodium excretion by 0.34 +/- 0.22% (P = 0.003) in control subjects. High-dose (2 mu g/min) ANP increased natriuresis to a similar ext ent in both groups. Insulin's antinatriuretic effects predominated over the natriuretic effects of low-dose, but not high-dose, ANP. These data sugges t that insulin's antinatriuretic effect is localized at a distal tubular si te other than the long loops of Henle and that the long loops are involved in the natriuretic effect of low-dose ANP, possibly mediated by changes in medullary blood flow.