Regulation of local cerebral blood flow in normal and hypoxic newborn dogs

Abstract

Local cerebral blood flow (LCBF) was measured autoradiographically in newborn puppies by an indicatorfractionation technique using 4-iodi-[¹⁴C]antipyrine as the diffusible indicator. Measurements were obtained in unanesthetized, normotensive animals, and the sensitivity of blood flow to hypercapnia and acute hypoxia was determined in 32 brain structures. LCBF in normal and hypoxic puppies was correlated with local cerebral glucose utilization (LCGU) obtained under the same experimental conditions (Duffy et al, 1982). In normocapnic (Pa_CO2 33 mm Hg) control animals, highest rates of blood flow were found in gray matter nuclei of the brainstem, in the medulla oblongata, and in the posterolateral nucleus of the thalamus (50 to 77 ml/100 gm/min); far lower flows were recorded among white matter structures (5 to 11 ml/100 gm/min). The vasodilatory response to both hypercapnia and hypoxia was greatest among brainstem gray matter structures, intermediate among cortical and diencephalic gray matter structures, and least in white matter. When LCBF was plotted as a function of LCGU for control animals, a positive linear correlation was obtained for all structures (p < 0.001), implying that in newborns, as in adults, cerebral blood flow and metabolism are physiologically coupled. In hypoxic puppies, no consistent relationship between LCGU and LCBF could be demonstrated; however, there was a suggestion that the two measurements correlated inversely, presumably reflecting enhanced anaerobic glycolysis in structures (e.g., hemispheric white matter) that were not adequately protected by compensatory hyperemia. White matter damage, a frequent complication of perinatal hypoxia-asphyxia, may be a consequence in part of the limited capacity of white matter to vasodilate in response to the chemical “signals” of hypercapnia and lactic acidosis.