Cholinergic regulation of cyclic nucleotide levels, amylase release, and K + efflux from rat parotid glands

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Carbachol increased amylase release and K + efflux from rat parotid tissue slices. The amount of amylase released was small compared to that released by isoproterenol. The effect of carbachol on amylase release and K + efflux was a direct effect. This conclusion was based on the finding that the stimulatory effects of carbachol were blocked only by atropine and not by propanolol or phentolamine. In addition to the above effects, carbachol also caused a rapid increase in the parotid guanosine-3',5' cyclic monophosphate (cGMP) levels without a discernable effect on adenosine-3',5' cyclic monophosphate (cAMP) levels. The increase in cGMP level caused by carbachol was blocked by atropine and not by phentolamine. The stimulatory effect of carbachol on amylase release was not additive with that of isoproterenol or dibutyryl cAMP. Although carbachol had no effect on basal cAMP levels it did inhibit increases in cAMP caused by isoproterenol. Similarly isoproterenol inhibited increased in parotid cGMP levels caused by carbachol. Unlike the apparent nonadditivity between the effects of isoproterenol and carbachol on amylase release and cAMP and cGMP accumulation, the effects on K + efflux were additive. The possibility of a role for cGMP in mediating the effects of cholinergic agonists on K + efflux was lessened by our observations that 1-methyl-3-isobutylxanthine enhanced the effect of limiting concentrations of carbachol on cGMP accumulation while not enhancing the effects of carbachol on K + efflux.