Insulin inhibits glucagon-induced glycogenolysis in perivenous hepatocytes specifically.
Hepatocytes form the hepatic acinus as the unit of microcirculation. Following the bloodstream, at least 2 different zones can be discerned: the periportal and perivenous zones. Two types of hepatocytes, periportal hepatocytes (PPHs) and perivenous hepatocytes (PVHs), have been thought to be functionally heterogeneous, with PPHs being predominantly gluconeogenic and PVHs being glycolytic. We therefore investigated the region-specific functional effects of insulin on glycogen synthesis, glycolysis, glycogenolysis, and gluconeogenesis in isolated PPHs and PVHs prepared by using the digitonin-collagenase method. Glycogen synthesis from 5 to 20 mmol/L glucose did not differ between the PPHs and PVHs of fed rats during 60 minutes of incubation. Lactate release induced by 5 to 20 mmol/L glucose was 3 times greater from PVHs than from PPHs (P <.01). The addition of insulin did not accelerate either glycogen synthesis or lactate release during 60 minutes of incubation. Insulin did not inhibit glucose release from gluconeogenic substrates with or without 0.2 nmol/L glucagon in either the PPHs or the PVHs of fasting rats. Insulin antagonized the 0.1 nmol/L glucagon-induced increase in glucose release from the PVHs of fed rats during 30 minutes of incubation (to 56.1% +/- 7.2%, P <.01) but not that from the PPHs (to 81.8% +/- 7.3%, P =.10). Thus the antagonizing effect was greater in PVHs than in PPHs (P <.01). Insulin binding did not differ between the PPHs and PVHs of fed rats. It was confirmed that PVHs are actually glycolytic. An acute metabolic effect of insulin was observed only in antagonizing glucagon-induced glycogenolysis in PVHs specifically. The specific effect of insulin on PVHs might depend on the differences in intracellular characteristics between PPHs and PVHs rather than hormone binding.
Ikezawa
Y
Y
Third Department of Internal Medicine, Yamagata University School of Medicine, Japan.
Yamatani
K
K
Ohnuma
H
H
Igarashi
M
M
Daimon
M
M
Manaka
H
H
Sasaki
H
H
D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005934:Glucagon / Q000494:pharmacology; D005943:Gluconeogenesis / Q000187:drug effects; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D019344:Lactic Acid / Q000378:metabolism; D008112:Liver Glycogen / Q000378:metabolism*; D008297:Male; D008833:Microcirculation / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar
D007328:Insulin; D008112:Liver Glycogen; D019344:Lactic Acid; D005934:Glucagon