Changes in blood glucose concentration in the carotid body-sinus modify brain glucose retention
To test whether blood glucose concentration in the carotid body-sinus may influence the amount of glucose retained by the brain, the isolated carotid sinus was perfused with glucose-rich blood or glucose-poor blood from a second animal. The circulation of the right carotid body-sinus was temporarily isolated in rat A, and perfused with blood coming from rat B. Blood glucose in rat B was modified by injections of glucose or insulin. Changes in glucose retention by the brain were measured in rat A. When the isolated carotid body-sinus in rat A was perfused with hyperglycemic blood (16.7 mM), brain glucose retention in rat A decreased significantly from 0.14 +/- 0.02 mumol/g/min (t = 0) to 0.08 +/- 0.01 mumol/g/min at 4 min after the beginning of perfusion. In contrast, the perfusion of the isolated carotid body-sinus of rat A with hypoglycemic blood (2.7 mM) from rat B, had the opposite effect. Brain glucose retention in rat A increased (0.23 +/- 0.03 mumol/g/min) at t = 4 min in comparison to control values (0.13 +/- 0.01 mumol/g/min). Chemoreceptor activity was also manipulated by the injection of cyanide (NaCN) in rat B, under these conditions, brain glucose retention in rat A increased from 0.13 +/- 0.01 mumol/g/min to 0.28 +/- 0.03 mumol/g/min between 4 to 8 min after the beginning of perfusion. These results indicate that chemosensory activity within the carotid body-sinus, superfused in vivo with different glucose concentrations, modify glucose retention by the brain.
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