Sensitivity of central chemoreceptors controlling blood glucose and body temperature during glucose deprivation.

Abstract

1. The rise in blood glucose and the fall in body temperature which follows the injection of a glucose analogue, 2-deoxy-D-glucose (2-DG) into the lateral cerebral ventricle (I.C.V) of unanaesthetized rats were studied and found to be dose-dependent. These 2-DG induced responses are elicited by the impairment of glucose metabolism within central "glucoreceptors'. 2. 2DG induced hyperglycaemia and hypothermia were completely prevented and even the converse effects occurred when fivefold equimolar amounts of D-fructose were simultaneously injected I.C.V.; fructose, at equimolar doses, did not modify the effects of 2-DG. 3. D-xylose and D-ribose, even at high doses, did not influence 2-DG hyperglycaemia, but increased slightly the 2-DG induced hypothermia. This suggests that the pentose phosphate pathway is unable to support the metabolism within the glucoreceptors. 4. Pyruvate suppressed the 2-DG induced hyperglycaemia with a marked delay, while acetate (as ethyl ester) and a mixture of malate plus oxaloacetate did not prevent 2-DG induced effects. These results may be accounted for by the low dosage used. 5. Acetoacetate and 3-hydroxybutyrate did not prevent 2-DG hypothermia and hyperglycaemia. 6. An effective prevention of the 2-DG induced hyperglycaemia and hypothermia was achieved with fumarate and glutamate, indicating that the stimulation of the Krebs cycle within "glucoreceptors' removes the glucoprivic effects. 7. The results indicate that prevention of 2-DG induced effects occurred only with alternate source of metabolic fuel which can support high respiratory rates in brain tissue. It is concluded that central chemoreceptors are not specifically responsive to glucose, or hexoses, but to the rate of oxidative metabolism.