Mechanism of vasodilation induced by alpha‐human atrial natriuretic polypeptide in rabbit and guinea‐pig renal arteries.

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Abstract
Effects of alpha‐human atrial natriuretic polypeptide (alpha‐HANP) on electrical and mechanical properties of smooth muscle cells of the guinea‐pig and rabbit renal arteries and of the guinea‐pig mesenteric artery were investigated. alpha‐HANP (up to 10 nM) modified neither the membrane potential nor resistance of smooth muscle cells of the guinea‐pig and rabbit renal arteries. In the guinea‐pig mesenteric and renal arteries, alpha‐HANP (up to 10 nM) had no effect on the amplitude and facilitation (mesenteric artery) or depression (renal artery) of excitatory junction potentials nor on action potentials. In the guinea‐pig renal artery, alpha‐HANP (up to 10 nM) had no effect on the depolarization induced by noradrenaline (NA) (up to 10 microM) but markedly inhibited NA‐induced contraction. alpha‐HANP (10 nM) slightly inhibited the K‐induced contraction. In the rabbit renal artery, alpha‐HANP (10 nM) inhibited the NA‐induced contraction and to a lesser extent the K‐induced contraction. In the rabbit renal artery, the effects of alpha‐HANP on the release of Ca from the cellular storage by two applications of NA, and its re‐storage, were investigated in Ca‐free solution containing 2 mM‐EGTA. When 5 nM‐alpha‐HANP was applied before and during the first application of 0.5 microM‐NA, the contraction was markedly inhibited but the contraction to a second application of 10 microM‐NA was potentiated. If the first dose of NA was 10 microM the effect was very small. Under the same experimental procedures, nitroglycerine (10 microM) showed almost the same effects as alpha‐HANP on the NA‐induced contractions. When both the first (3 mM) and second (10 mM) contractions were evoked by caffeine in Ca‐free solution, alpha‐HANP (5 nM) and nitroglycerine (10 microM) inhibited both contractions to the same extent. In the rabbit renal artery, applications of alpha‐HANP or nitroglycerine increased the amount of guanosine 3',5'‐phosphate (cyclic GMP) in a dose‐dependent manner. However, a much higher concentration of nitroglycerine was required (2 X 10(3) times). In the rabbit renal artery, hydrolysis of phosphatidyl inositol 4,5‐bisphosphate (PI‐P2) activated by 0.5 microM‐NA was inhibited by alpha‐HANP, in a dose‐dependent manner, but activation by 10 microM‐NA was not inhibited by alpha‐HANP (up to 100 nM).(ABSTRACT TRUNCATED AT 400 WORDS)