Age-dependent change in the response of isolated beagle cerebral arteries to vasoactive agents.

Responses to vasoactive agents were compared in helical strips of cerebral arteries from beagles of different ages (30 days, 3 months, 1 year, and 3 years old). Contractile responses to norepinephrine, serotonin, and histamine, relative to those induced by 30 mM K+, were greater in the infant (30-day-old) beagle arteries than in those from the older beagles. Angiotensin II-induced contractions did not differ in these arteries, whereas relaxations induced by the peptide, converted to contractions by indomethacin, were greater in the arteries from adult beagles than in the immature beagle arteries. Relaxations induced by nicotine, due to stimulation of vasodilator nerves, and those induced by a small amount of K+, mediated by activation of the electrogenic Na+ pump, were not dependent on age. Infant beagle cerebral arteries responded to prostacyclin (PGI2) with a greater relaxation, whereas isoproterenol produced greater relaxations in the adult beagle arteries. It may be concluded that the sensitivity or the quantity of alpha 2-adrenergic and H1-histaminergic receptors is high in the cerebral arteries of infant beagles and declines with age; the affinity of serotonergic receptors decreases with age. Biosynthesis of PGI2 in the vascular wall appears to increase with age. Functions of the vasodilator nerve innervating large cerebral arteries and of the electrogenic Na+ pump in muscle cell membranes may mature during the fetal or early postpartum period and, thereafter, are maintained unaltered.