To elucidate the loci for the putative
glucoreceptors responding to
hypoglycemia we introduced 'brain' and 'liver' clamps. Systemic
hypoglycemia was induced by
insulin infusion while the area of interest (ie. forebrain, hindbrain, portal-hepatic region) was maintained euglycemic via local
glucose irrigation. Utilizing this approach, there appear to be no
glucoreceptors residing exclusively in either the forebrain or hindbrain which are essential for the sympathoadrenal response to
hypoglycemia. This is true for both moderate and severe
hypoglycemic conditions. The possibility of a redundant glucoreceptor system within the brain, as suggested by a subsequent study, remains to be confirmed. The portal-hepatic
glucoreceptors appear essential to engendering the full counterregulatory response. Establishing euglycemia across the portal-hepatic region inhibits the sympathoadrenal response to moderate
hypoglycemia by over 40%. Further, despite prevailing
hypoglycemia and significant elevations in counter-regulatory
hormones, the liver demonstrated net
glucose extraction during the liver clamp, suggestive of overriding neural input to the liver. Thus, the hepatic afferents appear to be very important for the counterregulatory response to
hypoglycemia.