The effects of aging and diabetes on the distribution of β- adrenoceptor subtypes in the gut were investigated in the BB rat. [125I]Cyanopindolol binding to 10-μm sections was evaluated using film autoradiography. Cyanopindolol binding to β-, β1-, and β2-adrenoceptors was displaced by 1 μM propranolol, 50 nM ICI-89-406, and 100 nM ICI-118- 551, respectively. β-Adrenoceptor binding was highest in the circular muscle of proximal colon and lowest in the pylorus of 4- to 5-month-old rats. Aging (8- to 10-month-old vs. 4- to 5-month-old rats) was associated with increased β-adrenoceptor binding in the pylorus and reduced binding in the proximal colon. Diabetes had a time-dependent effect on the level of β-adrenoceptor binding. It was increased in the antral and pyloric stomach but longer periods of diabetes caused a reduction in β-adrenoceptor binding in the pylorus. Those in the intestine were reduced time-dependently and involved β1-or β2-adrenoceptors or both.
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