Abstract
Penetration of sucrose from blood into brain which is very slow in the adult has been used to investigate the development of the blood-brain barrier (BBB) in fetal and neonatal sheep. Approximately constant blood levels of 14C sucrose have been maintained by an intermittent intravenous injection technique over 1½ hr, after which cerebrospinal fluid and brain were removed. their 14C activity was measured and compared with that in the blood during the 1½ -hr injection period. Fetuses as young as 100 days gestation have a barrier to 14C surcrose which is similar to that found in adult animals. However, fetuses at term (1.40 days) and newborn lambs show an increase of about 300% in sucrose penetration when made severely hypercapnic (arterial pCO2 > 90 mm Hg). A smaller effect occurs at lower levels of pCO2. The effect of CO2 is also less in older animals. In other experiments, acidosis induced by slow intravenous infusion of 2N-lactic acid has little effect on sucrose penetration, although arterial pH was as low as that in the hypercapnic animals. Asphyxia produced intermittent cord occlusion in the fetus or underventilation in newborn lambs did not affect sucrose penetration unless anterial pCO2 showed a sustained rise above about 60 mm Hg. A possible explanation for the effect of hypercapnia is that the increase in cerebral blood flow which occurs in hypercapnia may cause more sucrose penetration because of the increased surface area for exchange across the BBB. Krypton-85 clearance has been used to estimate superficial cortical blood flow. Preliminary observations suggest a correlation between cortical blood flow and sucrose penetration into cortical tissue since both appear to be proportional to arterial pCO2, other possibilities being considered are (1) a direct effect of CO2 upon the permeability of the barrier. (2) an increase in the size of the brain extra-cellular space.
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Evans, C., Reyolds, J., Reynolds, M. et al. 42. Effect of hypercapnia on a blood-brain barrier in fetal and neonatal sheep. Pediatr Res 5, 92 (1971). https://doi.org/10.1203/00006450-197102000-00047
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DOI: https://doi.org/10.1203/00006450-197102000-00047