RESPONSIVENESS OF HUMAN INFANT CEREBRAL-ARTERIES TO SYMPATHETIC-NERVESTIMULATION AND VASOACTIVE AGENTS

Responses of segments of basilar and middle cerebral arteries of eight human infants to activation of perivascular nerves and to vasoactive drugs were studied using a resistance artery myograph. The infants age s ranged from 23 wk of gestation to 34 postnatal days. Neurogenic vaso constriction occurred in all segments and at 8 Hz was 12.7 +/- 3.5% (1 1%) of tissue maximum and was blocked by phentolamine (10(-6) M). Ther e was no evidence of a neurogenic dilator response. Catecholamine hist ofluorescence was seen in nerves in the adventitia at all ages studied . Norepinephrine ED,, was 7.6 +/- 1.8 X 10(-7) M, and its maximum effe ct was 43.1 +/- 5.7% of tissue maximum. Both neural and norepinephrine responses were greater than those of the proximal parts of adult huma n middle cerebral arteries obtained postmortem and surgically removed adult human pial arteries. Electron microscopy demonstrated that neura l density at the adventitiomedial junction in the infant vessels was g reater than in the pial arteries. Constrictor responses to serotonin a nd prostaglandin F-2 alpha were minimal in the two infants of 23 and 2 4 wk of gestation but were clearly present in the older infants. Hista mine and acetylcholine were potent vasodilators. Indomethacin potentia ted agonist-induced contraction. In a limited number of trials angiote nsin II, neuropeptide Y, caused contraction and bradykinin, relaxation . It is concluded that there is a quantitative similarity between the studied responses of infant cerebral artery segments and human pial ar teries of similar diameter. However, sympathetic nerves may potentiall y play a more important role in the regulation of cerebrovascular tone in the infant compared with the adult, and during the gestational per iod examined these vessels possess an indomethacin-sensitive system th at buffers agonist tone.