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 preterm and early postnatal infants have been examined using the resistance artery myograph technique for wire-mounted segments and the pressure perfusion arteriograph. Myograph-mounted segments spontaneously developed tone of varying duration and time course. Perfused segments showed maintained tone levels of approximately 40% of maximum possible constriction when the intraluminal pressure was 60 mm Hg. This level is not different from that found in adult human pial arteries of similar lumen 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 increase 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 higher levels decreased by intraluminal flow. The pressure/diameter curves 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 endogenous indomethacin-sensitive process.