Carbachol stimulation of inositol phosphate accumulation in rat submandibular gland fragments is not modified by VIP

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Abstract
Formation of inositol phosphates in response to carbachol, phenylephrine and vasoactive intestinal polypeptide (VIP) was studied after labelling with [3H]myo‐inositol in rat submandibular gland fragments. Carbachol enhanced the accumulation of inositol phosphates in a concentration‐dependent manner. This effect was independent of calcium in the incubation medium and totally antagonized by atropine (IC50= approx.1 nM).Phenylephrine also induced an increase in inositol phosphate accumulation, which was totally antagonized by prazosin but not by atropine. Vasoactive intestinal polypeptide, isoproterenol and forskolin, compounds known to enhance the levels of cAMP in rat salivary gland, or addition of dibutyryl‐cAMP (DB‐cAMP) failed to alter basal or carbachol‐evoked accumulation of inositol phosphates.It is concluded that the formation of inositol phosphates during muscarinic receptor stimulation with carbachol in rat submandibular gland fragments is not affected by adrenoceptor occupation or by cAMP.In particular, addition of VIP, which coexists with acetylcholine, did not alter the muscarinic inositol phosphate response.