INTRINSIC TONE OF CEREBRAL-ARTERY SEGMENTS OF HUMAN INFANTS BETWEEN 23 WEEKS OF GESTATION AND TERM

Segments of basilar and middle cerebral arteries of eight human preter m and early postnatal infants have been examined using the resistance artery myograph technique for wire-mounted segments and the pressure p erfusion arteriograph. Myograph-mounted segments spontaneously develop ed tone of varying duration and time course. Perfused segments showed maintained tone levels of approximately 40% of maximum possible constr iction when the intraluminal pressure was 60 mm Hg. This level is not different from that found in adult human pial arteries of similar lume n diameter. Indomethacin (10(-5) M) either initiated tone increase or potentiated existing tone in the isometrically mounted segments. After washout of vasoconstrictors norepinephrine (10(-6) M) and angiotensin II (10(-8) M), indomethacin caused a pronounced, long lasting increas e in basal tone. Spontaneous tone was reversed by acetylcholine (10(-6 ) M), isoproterenol (10(-8) to 10(-5) M), histamine (10(-8) to 10(-5) M), and papaverine (10(-5) M). Low levels of tone were increased and h igher levels decreased by intraluminal flow. The pressure/diameter cur ves of these vessels were of similar shape as those of the equivalent size in the adult. It is concluded that intrinsic tone is a prominent feature of these large cerebral arteries, and it is modified by an end ogenous indomethacin-sensitive process.