The response of the cerebral vasculature to changes in blood flow is an important component of autoregulation. Appropriate responses, i.e. vasodilation or vasoconstriction, may be especially important during the neonatal period, when marked changes in cardiac output and its distribution occur. Methods: To characterize the effect of maturation on the response to flow, we studied cerebral arteries from one week old and adult guinea pigs. Cerebral artery segments were cannulated and pressurized. Increasing intraluminal flow was delivered in a stepwise fashion from 0.02 to 1.0 ml/min. Transmural pressure was maintained constant throughout the study. Changes in diameter were measured using a videomicroscaler.Results: Adult cerebral arteries (n=4) demonstrated flow-dependent constriction throughout the range tested (Figure). In contrast, newborn cerebral arteries (n=4) demonstrated a biphasic response: at low flows (≤ 0.33ml/min) arteries constricted while at higher flows, they dilated to their resting diameter. This age-related difference was significant(p<0.001, two-way ANOVA). Conclusion: Cerebral arteries from newborns demonstrate a biphasic response to flow not observed in arteries from adults. This unique response may be a key feature of the cerebral adaptation to circulatory change at birth.

figure 1