Increase in potassium release from rat parotid tissue repeatedly exposed to isoproterenol.

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Abstract
The effect of repeated exposure to isoproterenol (ISO) in parotid tissue was investigated with regards to K release in response to a successive challenge of .alpha.- and .beta.-adrenergic agonists. An increase in K release by epinephrine was potentiated in the parotid tissue from rats repeatedly administered ISO (3 mg/kg, 3 times daily for 3 days). A decrease in the release by ISO disappeared in ISO-pretreated glands. Cycloheximide and actinomycin D, administered with ISO, completely blocked the ISO-induced development of the enhanced response to epinephrine, but not that of the reduced response to ISO. After in vitro pretreatment with ISO, the K release induced by a successive dose of ISO was higher than the basal release of the electrolyte. The same treatment showed a tendency to increase the response to norepinephrine. The increased release induced by a challenge dose of ISO disappeared in the tissue from cycloheximide-treated rats. The ISO-induced increase of K release which was caused by ISO-pretreatment in vitro was inhibited by prazosin, but not by yohimbine and propranolol. The .alpha.-adrenergic response in parotid tissue may be potentiated by exposure to ISO.
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