Extra‐pancreatic action of glibenclamide in man: reduction in vitro of the inhibitory effect of glucagon and epinephrine on the hepatic key glycolytic enzymes phosphofructokinase (PFK) and pyruvate kinase (PK)

Abstract

Human liver slices (surgery biopsies) were preincubated with glucagon or epinephrine for 10 min at 37 degrees C in Krebs-Henseleit solution at pH 7.4, in the absence or presence of glibenclamide, and then homogenized and assayed for phosphofructokinase (PFK) and pyruvate kinase (PK) activity at subsaturating, near physiological, substrate concentrations (suitable for detecting regulatory effects). Preincubation with 10 microM glucagon (n = 7) or 10 microM epinephrine (n = 7) resulted in a reduction of PFK activity of 25% (P less than 0.02) and 29% (P less than 0.05), respectively. Addition of 2 microM glibenclamide in the preincubation mixture reduced the inhibitory effect of glucagon by 99% (P less than 0.05) and that of epinephrine by 70% (P less than 0.01). Likewise, 10 microM glucagon (n = 6) or 10 microM epinephrine (n = 4) reduced PK activity by 40% (P less than 0.01) and 46% (P less than 0.01), respectively. Addition of 2 microM glibenclamide significantly reduced the inhibitory effect of glucagon by 77% (P less than 0.05) and that of epinephrine by 33% (P less than 0.05). In the absence of the hormones, glibenclamide was without effect. Thus, glibenclamide opposes the inhibitory effect of glucagon and epinephrine on two key hepatic glycolytic enzymes. Since the inhibition of key glycolytic enzymes favours gluconeogenesis, the observed action of glibenclamide, if it occurs also in vivo, might reduce the glucagon- and epinephrine-stimulated gluconeogenesis, and could be regarded as an insulin-like action.