Attenuation of responses of ANP release to adrenergic receptor agonists in cold exposed rats

Abstract

It has been known that chronic cold exposure resulted in a sustained increase in blood pressure in rats. The aim of the present study was to define the direct effects of adrenergic receptors agonists on atrial hemodynamics and ANP release in cold exposed rats. Cold exposure for 2 weeks resulted in marked increases in urine volume and water retention. Plasma renin activity was decreased and plasma level of ANP was increased by cold exposure. Phenylephrine increased the ANP release from isolated perfused beating rat atria whereas isoproterenol decreased the ANP release with positive inotropism in a dose‐dependent manner. The amounts of cAMP in perfusate were not affected by phenylephrine, but increased by isoproterenol. The effects of phenylephrine on atrial ANP release was attenuated in cold exposed rats. Isoproterenol‐induced decrease in ANP release, positive inotropy and increase in cAMP production were also attenuated in cold exposed rats. Real‐Time PCR analysis showed £\ƒ¡a and £]ƒ¡ ƒnadrenergic receptors mRNA levels were significantly decreased in cold exposed rats. These results suggest that £\ƒ¡a and £]ƒ¡ adrenergic receptors differently regulate atrial ANP release and hemodynamics, and the attenuation of response to adrenergic receptor agonists in cold exposed rats may be partly related to the downregulation of £\ ƒnandƒn £] ƒ{adrenergic receptors.Supported by the KOSEF R01‐2006‐000‐10554‐0.