Developmental changes in thickness, contractility, and hypoxic sensitivity of newborn lamb cerebral arteries.

The present studies were conducted to examine the possibility that the increased vulnerability of the newborn brain to hypoxia may be due to age-related differences in vascular thickness and contractility. Segments of rostral choroidal (RC), posterior communicating (PC), basilar (B), and common carotid (CC) arteries were taken from 3- to 7-day-old lambs (n = 11) and adult sheep (n = 8) and studied using standard in vitro techniques. In lamb cerebral arteries, maturation was associated with significant increases in vessel thickness and tension generation. Because the increases in tension generation (77, 90, and 135% in PC, B, and RC segments) were proportionately greater than the corresponding increases in thickness (45, 75, and 34% in PC, B, and RC), force per unit area increased with maturation in the cerebral arteries. In the CC segments, the age-related increases in thickness (117%) were greater than the increases in tension generation (30%), such that average force per unit area was actually greater in the lamb than in the sheep. In response to hypoxia (PO2 less than 15 torr), all vessels exhibited significant relaxation relative to normoxic controls, although the rates and magnitudes of relaxation varied considerably. In the sheep, the carotid exhibited rapid relaxation of small magnitude (21%), whereas the cerebral arteries relaxed more slowly and more completely (56, 52, and 45% in PC, B, and RC). In contrast, the lamb carotid segments relaxed more slowly than the cerebral arteries.(ABSTRACT TRUNCATED AT 250 WORDS)