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Hypoglycemic Detection Does Not Occur in the Hepatic Artery or Liver

Findings Consistent With a Portal Vein Glucosensor Locus

From the Departments of Exercise Science (A.L.H., C.M.D.) and Physiology and Biophysics (R.N.B.), University of Southern California, Los Angeles, California.

Address correspondence and reprint requests to Dr. Casey M. Donovan, University of Southern California, Dept. of Exercise Science, PED 107, 3560 S. Watt Way, Los Angeles, CA 90089-0652. E-mail: donovan{at}usc.edu .

Our laboratory has previously demonstrated that hypoglycemic detection occurs in the portal vein, not the liver. To ascertain whether hypoglycemic detection may also occur in the hepatic artery, normoglycemia was established across the liver via a localized hepatic artery glucose infusion. Male mongrel dogs (n = 7) were infused with insulin (5.0 mU · kg^-1 · min^-1) via the jugular vein to induce systemic hypoglycemia. Animals participated in two hyperinsulinemic-hypoglycemic clamp experiments distinguished by the site of glucose infusion. During the liver irrigation protocol, glucose was infused via the hepatic artery (HA protocol) to maintain liver normoglycemia as systemic glucose concentrations were systematically lowered over 260 min (nadir = 2.2 ± 0.01 mmol/l). During control experiments, glucose was infused peripherally (PER protocol) to control reductions in blood glucose. Arterial glucose concentrations were not significantly different at any time between the two protocols (P = 0.73). Hepatic artery and liver glucose concentrations were significantly elevated in the HA versus PER protocol throughout the duration of the progressive hyperinsulinemic-hypoglycemic clamp. During the PER protocol, epinephrine and norepinephrine concentrations increased significantly above basal values (0.53 ± 0.06 and 0.85 ± 0.2 nmol/l, respectively) to plateaus of 4.4 ± 0.86 (P = 0.0001) and 3.6 ± 0.69 nmol/l (P = 0.001), respectively. There were no significant differences between the two protocols in the epinephrine (P = 0.81) and the norepinephrine (P = 0.68) response to hypoglycemia. The current findings indicate that glucosensors important to hypoglycemic detection do not reside in the hepatic artery. Furthermore, these data confirm our previous findings that glucosensors important to hypoglycemic detection are not present in the liver, but are in fact localized to the portal vein.

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