Unidirectional transport of glucose and lactate into brain of fetal sheep and guinea-pig.
The first-passage multiple-indicator dilution method was used to measure blood to brain transport of D- and L-glucose, D- and L-lactate and sucrose relative to 22Na, an impermeable reference tracer, in fetal sheep. Fractional extraction for D-glucose was 0.315 +/- 0.051 (S.E.M.) at normal glucose levels and fell to 0.198 +/- 0.041 at 5.2 +/- 0.4 mM-glucose. Fractional extractions for L-glucose, D- and L-lactate and sucrose were not different from zero. No specific blood-brain transport system was detected for L-lactate in fetal sheep in vivo (fractional extraction = -0.024 +/- 0.019). Uptake of L-lactate into isolated microvessels from fetal sheep cerebrum in vitro showed a slightly higher rate (32.2 +/- 8.9 pmol min-1 (mg protein)-1) than that for D-lactate (22.6 +/- 5.6). In fetal guinea-pigs, the carotid arterial injection method with tritiated water as the permeable reference was used to measure the brain uptake index (BUI). BUI was determined for D-glucose (0.304 +/- 0.065) sucrose (0.008 +/- 0.001), L-lactate (0.418 +/- 0.112) and D-lactate (0.071 +/- 0.024). Unidirectional influx calculated from these measurements and estimates of cerebral blood flow showed that transport would be rate-limiting for cerebral glucose utilization at arterial glucose levels below 0.5 mM in fetal sheep and 1.7 mM in fetal guinea-pig. In fetal sheep, but not in fetal guinea-pigs, lactate efflux may be limited by brain-blood transport.
Bissonnette
J M
JM
Department of Obstetrics and Gynecology, Oregon Health Sciences University, Portland 97201.
Hohimer
A R
AR
Chao
C R
CR
D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D001812:Blood-Brain Barrier; D001921:Brain / Q000196:embryology / Q000378:metabolism*; D002560:Cerebrovascular Circulation; D005260:Female; D005333:Fetus / Q000378:metabolism*; D005865:Gestational Age; D005947:Glucose / Q000493:pharmacokinetics*; D006168:Guinea Pigs; D007773:Lactates / Q000493:pharmacokinetics*; D019344:Lactic Acid; D012756:Sheep
D007773:Lactates; D019344:Lactic Acid; D005947:Glucose