CARBOHYDRATE-METABOLISM AND HEPATIC ZONATION IN THE ATLANTIC HAGFISH,MYXINE-GLUTINOSA LIVER - EFFECTS OF HORMONES

Viable Atlantic hagfish (Myxine glutinosa) hepatocytes were isolated f rom combined or separated large and small lobes and carbohydrate metab olism was studied. Cells had low levels of glycogen (16-30 mumol.g-1), and low rates of total glucose production (TGP; 0-480 nmol.h-1.g-1 ce lls). Lactate flux to glucose (5.5 nmol.h-1.g-1) and CO2 (76 nmol.h-1. g-1) was lower than reported values for teleosts, with a low percentag e (30%) of the lactate carbon reaching glucose. Insulin significantly increased total glucose production and gluconeogenesis and decreased 6 -phosphofructo 1-kinase (PFK-1) activities and glucose oxidation, whil e glucagon was without effect on any parameter studied. Forskolin sign ificantly increased TGP. Epinephrine (Epi), norepinephrine (NEpi), iso proterenol (Iso), and phenylephrine (Phe) all decreased CO2 production from lactate; propanolol blocked the effects of Epi, NEpi, and Iso. T he large lobe, accounting for 65% of total liver mass, had a higher gl ycogen content and higher CO2 production from lactate compared to the small lobe. Furthermore, enzyme activities in the large lobe were grea ter than in the small lobe, with the exception of glycogen phosphoryla se (GPase) which exhibited smaller %a values in the large lobe. These data indicate the presence of a hormonally-responsive carbohydrate met abolism in hagfish hepatocytes, which is qualitatively and quantitativ ely different between the two liver lobes.