ADRENERGIC-RECEPTORS AND SECRETORY RESPONSES OF THE RAT SUBMANDIBULARSALIVARY-GLAND AFTER PERIODIC INCISOR REDUCTION

The lower and upper incisors of female rats were repeatedly reduced ev ery 48 hr for 21 days. A marked enlargement of the submandibular gland s was observed at the end of this period. One day after the final redu ction, dose-dependent curves to phenylephrine and isoproterenol were o btained in relation to salivary flow rates. Secretory responses, expre ssed as mg/gland, showed that the dose-response curve to the al-adreno mimetic drug was not modified by treatment while that for isoprotereno l was shifted to the right of the control. When the responses were exp ressed as mu g of saliva/mg of wet tissue, the dose-response curve to both agonists was shifted to the right in the incisor-reduced group. ( Activation of alpha(2)-adrenergic receptors by clonidine did not inhib it the responses to phenylephrine in the incisor-reduced rats.) Radiol igand binding assays of alpha(1)-, beta- and alpha(2)-receptors did no t show differences between control and experimental glands in terms of densities (B-max) or affinities (K-d) The lack of correlation between the decrease in alpha(2)- and beta-mediated responses and the radioli gand bindings suggests that postreceptor mechanisms are involved in th e diminished secretory responses of the rat submandibular gland after periodic reduction or amputation of incisors. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.