Regulation of metaraminol efflux from rat heart and salivary gland.
1. The turnover rate of noradrenaline (NA) in heart and submaxillary salivary gland was studied in rats exposed to 4 degrees C or maintained at room temperature (22 degrees C). Cold exposure increased the turnover of the NA store in heart but not in salivary gland.2. In another series of experiments the decline of metaraminol (M) from heart and submaxillary salivary gland was studied in rats exposed to 4 degrees C or maintained at room temperature. Cold exposure accelerated the efflux of M from heart, but not from salivary gland. It is concluded that the accelerated decline of M from heart is the consequence of selective activation of the sympathetic nerves that innervate the heart.3. The turnover of NA was studied in rat heart after the administration of M (100 mug/kg intravenously) or its precursor alpha-methyl-meta-tyrosine (200 mg/kg intraperitoneally). Turnover remained essentially normal after these drugs.4. The administration of desipramine (DMI, 20 mg/kg intraperitoneally) 1 hr after M (100 mug/kg intravenously) induced a rapid sustained efflux of M from heart and salivary gland. The results of this study suggest that the slow decline of M from heart is the result of the great affinity of the amine retrieval mechanism in sympathetic nerve endings for M. DMI inhibits the retrieval mechanism, thus accelerating the efflux of M.