Age-dependent changes in the response of isolated beagle coronary arteries to transmural electrical stimulation and catecholamines.

In helical strips of proximal and distal coronary arteries from beagles of different ages (30 days, 3 months and 1 and 3 years old) precontracted partially with prostaglandin F2 alpha, responses to catecholamines, transmural electrical stimulation, tyramine and acetylcholine were compared. Proximal coronary arteries from infant beagles responded to norepinephrine and epinephrine with contractions, whereas those from adult (1 and 3 years old) beagles responded with dose-related relaxations. Isoproterenol-induced relaxations were in the order of infant less than young less than adult beagle arteries. Norepinephrine produced contractions in the proximal arteries from infant beagles but relaxations in the distal arteries. Relaxations induced by norepinephrine and isoproterenol were in the order of small greater than medium greater than large-size arteries from adult beagles. Transmural stimulation and tyramine produced contractions in the infant and young beagle arteries of proximal portion but only relaxations in the adult beagle arteries. The contractions induced by transmural stimulation and norepinephrine were suppressed by prazosin but not by yohimbine. Acetylcholine produced similar magnitude of relaxations in the arteries from beagles of different ages. It may be concluded that contractions of coronary arteries mediated by alpha-1 adrenoceptors decrease with age, whereas beta receptor-mediated relaxations increase with age. Alpha-1 adrenoceptor functions appear to be in the order of large greater than medium greater than small-size coronary arteries from beagles of different ages, and beta receptor functions to be in the reverse order.