Blood–Brain Transfer of Glucose and Glucose Analogs in Newborn Rats

Authors


  • This work was presented in part at the Satellite Symposium to the Third World Congress for Microcirculation, Carrier-Mediated Transport of Solutes from Blood to Tissue, in London, September 6–7, 1984, and at the XII International Symposium on Cerebral Blood Flow and Metabolism, Brain 85, Lund-Ronneby, June 16–20, 1985. Part of the work was included in A.F.'s Honor Thesis.

Address correspondence and reprint requests to Dr. A. Gjedde at Medical Physiology Department A, The Panum Institute, Building 12, Room 5–14, 3, Blegdamsvej, Copenhagen, Denmark 2200.

Abstract

Abstract: Little is known of the selectivity of the blood–brain barrier at birth. Hexoses are transported through the barrier by a facilitating mechanism. To study the capacity of this mechanism to distinguish between analogs of D-glucose, we compared the transport of fluorodeoxyglucose, deoxyglucose, glucose, methylglucose, mannose, galactose, mannitol, and iodoantipyrine across the cerebral capillary endothelium in newborn Wistar rats. Cerebral blood flow, glucose consumption, and the blood–brain permeabilities of the hexoses were 25–50% of the adult values but the ratios between the permeabilities of the individual hexoses were similar to the ratios observed in adult rats. The mannitol clearance into brain was considerably higher than in adult rats (about 10-fold), indicating a higher endothelial permeability to small polar nonelectrolytes. The brain water content was higher in newborn than in adult rats and was associated with a higher steady-state distribution of labeled methylglucose between brain and blood. Hexose concentrations were determined relative to whole blood because the apparent erythrocyte membrane permeability to glucose was as high as in humans and thus considerably higher than in adult rats. The half-saturation concentration of glucose transport across the blood–brain barrier was considerably higher than in adult rats, about threefold, suggesting that net blood–brain glucose transfer is less sensitive to blood glucose fluctuation in newborn than in adult rats.

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