Cerebral oxygenation and blood flow in infant and young adult rats.

In vitro cerebral oxidative metabolism undergoes dramatic increases in infant rats between 10 and 20 days of age. To determine this was also the case in vivo, comparisons were made of cerebral blood flow (CBF) and oxygenation in rats at 10, 20, and 60-90 days of age, under pentobarbital sodium anesthesia. Measurements were made of CBF, arterial and venous O2 content, cerebral PO2 distributions, and the oxidation state of cytochrome-c oxidase (cytochrome aa3). CBF, O2 delivery, and O2 consumption all increased progressively with maturation. In contrast, cerebral PO2, cytochrome aa3 oxidation state, and O2 extraction fraction were higher in 20-day-old rats than in either 10-day-old or adult rats. We attribute this difference primarily to the high density of cerebral capillaries in the 20-day-old rat. We conclude that cerebral tissue PO2 and the oxidation state of cytochrome aa3 are determined by the density of perfused capillaries in addition to the more commonly accepted factors of cerebral O2 delivery and consumption.