Daily changes in beta-adrenergic sensitivity of rat submandibular gland. Correlation with beta-adrenoceptor rhythm

Neurons from the superior cervical ganglia (SCG) innervate the submandibula r gland and release noradrenaline during the dark phase of the daily photop eriod. Since in the pineal, another structure innervated by sympathetic neu rons, nocturnal activation of the SCG is associated with beta -adrenergic s ub- and super-sensitivity rhythms, the possible existence of similar phenom ena in the rat submandibular gland was assessed. Wistar female rats, kept o n a 14:10 light/dark cycle (light from 06:00 to 20:00 h), were sacrificed a t 09.00, 14:00, 20:00, 24:00 and 04:00 h. beta -Adrenoceptors were studied by H-3-dihydroalprenolol binding to membrane preparations. The equilibrium dissociation constant (K-d) did not change as a function of time while sign ificant daily variations in maximal binding values (B-max) were observed wi th a peak at 20:00 h. Changes in B-max correlated with a high response of a denylate cyclase to isoproterenol. In addition, when the response in saliva ry flow to isoproterenol was measured, a shift to the left (about 1 logarit hmic unit) in dose-response curves was observed at 19:00-20:00 h as compare d to 08:00-09:00 h. These daily variations in isoproterenol responsiveness seem not to depend on the pattern of eating since a 24-h starvation or a no cturnal starvation for 16-18 days did not abolish the morning-evening diffe rences in the salivary flow response to isoproterenol. Rather, the results suggest that the daily variations in isoproterenol response correlate with beta -adrenegic super- and sub-sensitivity phenomena associated with the ci rcadian release of noradrenaline from SCG neurons. (C) 2001 Elsevier Scienc e B.V. All rights reserved.