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These results strongly suggest that Ca(2+)-activated potassium channels and L type Ca(2+) channels may be involved in papaverine-induced vascular relaxation in rat basilar artery.

Neuropeptide Y (NPY) receptors are present in cardiac membranes. However, its physiological roles in the heart are not clear. The aim of this study was to define the direct effects of pancreatic polypeptide (PP) on atrial dynamics and atrial natriuretic peptide (ANP) release in perfused beating atria. Pancreatic polypeptides, a NPY Y4 receptor agonist, decreased atrial contractility but was not dose-dependent. The ANP release was stimulated by PP in a dose-dependent manner. GR 23118, a NPY Y4 receptor agonist, also increased the ANP release and the potency was greater than PP. In contrast, peptide YY (3-36) (PYY), an NPY Y2 receptor agonist, suppressed the release of ANP with positive inotropy. NPY, an agonist for Y1, 2, 5 receptor, did not cause any significant changes. The pretreatment of NPY (18-36), an antagonist for NPY Y3 receptor, markedly attenuated the stimulation of ANP release by PP but did not affect the suppression of ANP release by PYY. BIIE0246, an antagonist for NPY Y2 receptor, attenuated the suppression of ANP release by PYY. The responsiveness of atrial contractility to PP or PYY was not affected by either of the antagonists. These results suggest that NPY Y4 and Y2 receptor differently regulate the release of atrial ANP.

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