Effects of Repeated Exposure to Isoproterenol in Vivo and in Vitro on Amylase Release from Rat Parotid Tissue

Effects of repeated exposure to isoproterenol (ISO), in vivo and in vitro, were investigated on amylase release from rat parotid slices responding to secretagogues. Responses to ISO and dibutyryl cyclic AMP (DBcAMP) were reduced in the tissue from ISO-treated rats (3 mg/kg, 3 times daily for 3 days), but not in the tissue from propranolol plus ISO-treated rats. Administration of inhibitors of protein synthesis with ISO resulted in a protective effect with regard to development of decreased responses to ISO, DBcAMP and carbachol. A decreased response to ISO (10(-5) M) was caused by repeated exposure to ISO in vitro and could not be prevented by pretreatment with inhibitors of protein synthesis. Although the basal level of cyclic AMP in parotid tissue was lower in ISO-pretreated rats than in control rats, after incubation with ISO, the level of cyclic AMP did not differ between ISO-pretreated and control rats. These results suggest that the decreased response (amylase release) to ISO in the parotid tissue from ISO-pretreated rats may have been due to an impairment of common secretory process(es) involving various secretagogues and that the development of the impairment may be closely connected to the de novo synthesis of proteins induced by ISO, but not the impairment of the beta-adrenoceptor-adenylate cyclase system.