Regulation of submaxillary gland muscarinic receptors during heat acclimation.
Binding properties of submaxillary gland muscarinic receptors and agonist-induced saliva secretion were studied in rats subjected to heat acclimation. The maximal binding capacity for the muscarinic antagonist N-[3H]methyl-4-piperidyl benzilate was increased from control value of 0.21 to 0.40 pmol/mg protein within 1-2 days of heat acclimation. The increase in the number of muscarinic receptors per gland (100%) was by far higher than the increase in tissue weight (20%), indicating higher density of receptors in the acinar cells of the treated rats. High levels of receptors coincided with the appearance of high-affinity binding sites for muscarinic agonists (oxotremorine, pilocarpine and carbamylcholine), and with reduced tissue sensitivity to pilocarpine. After 4-8 weeks of heat acclimation, the number of receptors as well as tissue response to pilocarpine returned to control levels. These results suggest a functional correlation between the transient upregulation muscarinic receptors in the submaxillary gland and the physiological activity in salivary secretion, and indicate that the high-affinity muscarinic receptors may attenuate saliva secretion during the initial phase of heat acclimation.
D000064:Acclimatization; D000818:Animals; D001833:Body Temperature Regulation; D006358:Hot Temperature; D008297:Male; D010277:Parasympathomimetics / Q000378:metabolism; D010862:Pilocarpine / Q000494:pharmacology; D051381:Rats; D011976:Receptors, Muscarinic / Q000502:physiology*; D012463:Saliva / Q000378:metabolism; D013363:Submandibular Gland / Q000187:drug effects / Q000502:physiology*
D010277:Parasympathomimetics; D011976:Receptors, Muscarinic; D010862:Pilocarpine