Response to deep hypoglycemia does not involve glucoreceptors in carotid perfused tissue

In the present study we examined whether the magnified hormonal counter-regulatory response seen during deep hypoglycemia (40 mg/dl) could be attenuated by supplying the forebrain with glucose furnished through carotid infusion. Two protocols were performed in conscious dogs. In the first protocol we infused glucose bilaterally into the carotid circulation to produce a forebrain glycemia of 55 +/- 1 mg/dl (as reflected in the jugular vein), whereas systemic glycemia declined to 39 +/- 2 mg/dl. In the second protocol as a control we infused glucose into the systemic circulation at a rate matched to protocol 1 so that both systemic and jugular plasma glucose concentrations were equivalent to the systemic glucose concentrations in protocol 1 (jugular, 41 +/- 3 mg/dl; systemic, 40 +/- 2 mg/dl; P greater than 0.9). In spite of a substantial difference in forebrain glycemia (55 mg/dl compared with 41 mg/dl) there were no differences in the counter-regulatory responses of catecholamines or glucagon. In addition, through the use of radiolabeled microspheres, we defined the precise regions of the forebrain irrigated during bilateral intracarotid glucose infusions. The concentration of microspheres was high in the forebrain but very low in the hindbrain. Our results indicate that glucoreceptor cells in tissues perfused by carotid arteries may play a tautological role in the sympathetic response to hypoglycemia and imply that glucose-sensitive receptors must also be located elsewhere in the central nervous system or in the periphery.