MODIFICATION OF THE BETA-ADRENERGIC SENSITIVITY OF RAT SUBMANDIBULAR-GLAND BY CONSTANT LIGHT

Rats exposed for 2, 5, 10, 20, 35 and 50 days to constant light (CL) s howed beta-adrenergic desensitization of the submandibular gland as in dicated by dose-response curves to 1.5, 2.0, 3.0, 10.0, 30.0 and 50.0 mu g/kg isoproterenol. The phenomenon, evident with 1.5, 2.0 and 50.0 mu g/kg after 2 days at CL, was more intense as time of exposure incre ased to reach values of about 50% those for controls after 20 days. Af ter 35 and 50 days, desensitization showed some reversion, but the sec retory responses were still lower than for controls maintained under a typical photoperiod. In the groups of rats exposed to CL for 20 days, gland wet and dry weights were higher (10%) than those of controls. T hese changes probably indicate an adaptation of the sympathetic contro l of salivary secretion induced by environmental illumination.