Cyclic adenosine 3',5'-monophosphate levels in response to norepinephrine in rectum of postnatal rats.

Age-related changes in cyclic adenosine 3',5'-monophosphate levels in response to norepinephrine (NE) in the rectum of postnatal rats and the localization of cyclic AMP in the rectum were studied. During the first 2 weeks after birth, the basal levels of cyclic AMP were high, NE responses to cyclic AMP contents were minimal and thereafter, the basal cyclic AMP levels rapidly declined, while NE response significantly increased compared to those seen in tissues from adult rats. Furthermore, cyclic AMP immunofluorescence was visualized in smooth muscle and postganglionic neurons of the myenteric plexus. NE application produced an increase of cyclic AMP immunofluorescence in smooth muscle. These results indicate that NE response to cyclic AMP levels in rat rectum is age-dependent and suggest that the majority of beta-adrenoceptors associated with cyclic AMP generating system are localized in the smooth muscle of rat rectum.