Neuroeffector function in mesenteric arteries isolated from beagles of different ages

In helical strips of mesenteric arteries from 30-day (28-35 day), 3-month (80-110 day), 2-year (10-40 month) and 12-year (135-161 month)-old beagles, contractile responses to vasoconstrictors were compared. The responses to transmural stimulation and norepinephrine, relative to those caused by 30 mM K+, were greater in the infant beagle arteries than in those from the older beagles. Equipotent concentrations of the amine for producing the same magnitude of contraction as that evoked by 5 or 20 Hz stimulation in beagles of different ages did not differ. Treatment with 10(-9) M prazosin or 10(-8) M yohimbine attenuated the response to norepinephrine in 30-day and 12-year-old beagles to a similar extent. Contractions induced by transmural stimulation in the infant beagle arteries were potentiated slightly by 10(-9) M yohimbine and, in contrast, attenuated at 10(-8) M. On the other hand, the stimulation-evoked contraction in the senile beagle arteries was potentiated by these concentrations of yohimbine in a dose-dependent manner. Angiotensin II potentiated responses to electrical stimulation in 30-day and 12-year-old beagles to a similar extent. Contractions by angiotensin II and serotonin did not alter with age. It may be concluded that alpha adrenoceptor function reduces during an early postnatal period, but does not decline further through senescence. It appears that prejunctional, but not postjunctional, alpha-2 receptor function develops after birth, whereas pre- and postjunctional angiotensin receptors already mature in beagles until the age of 30 days.