Atriopeptin III increases cGMP in glomeruli but not in proximal tubules of dog kidney

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Abstract
Atriopeptin III is natriuretic, diuretic, and phosphaturic in the intact dog and relaxes vascular and nonvascular smooth muscle in vitro. The mechanism of the renal effects of atriopeptin remains ill defined but may include hemodynamic alterations and/or direct tubular effects. Since many peptide hormones act through changes in cyclic nucleotide formation, we examined the effect of synthetic atriopeptins on cAMP and cGMP accumulation in isolated glomeruli and proximal tubules from normal dog kidney. Synthetic atriopeptin produced a dose-related increase in cGMP in glomeruli with a Kact of 200 +/- 19 nM and a maximal activity of 64.1 +/- 6.3 pmol cGMP X mg prot-1 X 5 min-1. In the presence of 4 mM Mn2+ Kact was reduced to 19 +/- 2 nM with no change in maximal cGMP production (66.2 +/- 11.8 pmol cGMP X mg prot-1 X 5 min-1). Atriopeptin (1 microM) did not increase cGMP accumulation above basal levels in proximal tubule segments. The cAMP production of neither glomeruli nor proximal tubules was stimulated by atriopeptin. These studies demonstrate a dose-dependent stimulation of guanylate cyclase by atriopeptin in glomeruli but not in proximal tubule segments. In addition, atriopeptin neither stimulates nor inhibits cAMP accumulation in glomeruli or proximal tubules. These data suggest a major role for the renal effects of atriopeptin at the glomerular level, possibly through hemodynamic effects or changes in the glomerular ultrafiltration coefficient.(ABSTRACT TRUNCATED AT 250 WORDS)

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