Rat salivary glands as a model for the study of adrenergic receptor modulation

The properties (kD and Bmax) of alpha-1 and alpha-2 adrenoceptors in rat submaxillary gland have been determined by the binding process of radioactive ligands. Data of dissociation constants compiled from several tissues by this technique closely agree with physiological measurements. The radioactive ligand binding method has afforded evidence for changes in receptor number elicited by procedures that induce either hyper or hyposensitivity of the response. Chemical sympathectomy with reserpine increases 10 fold the number of alpha-2 receptors in rat submaxillary gland, as determined by the binding of [3H] clonidine. Sympathetic surgical denervation also increases the number of alpha-2 adrenoceptors by about 50%. Alpha-1 adrenoceptors were studied using [3H] prazosin or [3H] WB 4101. In gangliectomized submaxillary glands, we did not find an increase in the number of binding sites. Alpha-1 and alpha-2 adrenoceptors are also modulated by the parasympathetic system. Sectioning of the chordalingual nerve 21 days before the experiment produces an increase of about 50% in both types of alpha adrenoceptors in the submaxillary gland. These results indicate a major modulatory role of the cholinergic system on postsynaptic adrenoceptors. This type of regulation has also been found in other tissues such as brown adipose tissue and in complex systems like the brain. The results show that the major salivary glands of the rat are a useful model for the study of adrenoceptor regulation and that the data obtained can be extrapolated to more complex systems.