Putative mediators of insulin action: regulation of pyruvate dehydrogenase and adenylate cyclase activities.

Abstract

Recent evidence suggests that certain actions of insulin may be mediated by the selective generation of chemically undefined intracellular substances. Incubation of rat liver particulate fraction with low concentrations of insulin enhances the release into the supernatant of a substance that stimulates mitochondrial pyruvate dehydrogenase. Higher concentrations of insulin release less stimulating activity. It is possible to resolve activities that stimulate and inhibit pyruvate dehydrogenase by differential ethanol extraction of the supernatant solutions. The elaboration of both factors is dependent upon the presence of insulin in a dose-dependent manner. Moreover, fractions that contain the pyruvate dehydrogenase-inhibiting activity also inhibit adipocyte basal and hormonally stimulated adenylate cyclase. The production of this adenylate cyclase inhibitory activity is also stimulated by insulin. Cyclase inhibition is virtually abolished when the nonhydrolyzable ATP analog, 5'-adenylyl imidodiphosphate, is included in the assay. These results indicate that the bimodal effects of insulin on certain functions may be ascribed to the generation of at least two distinct chemical substances that show opposing activities, which may operate by regulating phosphorylation reactions.

Insulin mediators in man: effects of glucose ingestion and insulin resistance

“…The lack of increase in the serum pH 1.3 IPG in the present study could thus be due to an insufficient increase in the extracellular insulin concentration, suggesting differential sensitivities of different IPG generating/releasing systems to insulin. Earlier it was shown in rat liver particulate fractions that the PDH activator increased in the presence of a low concentration of insulin while the adenylate cyclase inhibitor did not change at the same insulin concentration [10]. These findings support the idea of differential sensitivities of different IPGs to insulin.…”

“…To study the bioactivity of the PDH inhibitor, the same procedure as above was used, except that the mediator volume was equivalent to 2 m mol/ l) were added during the preincubation step. This increased PDH activity and facilitated detection of the inhibitor [10].…”

“…The PDH activating fraction has been shown also to contain an inhibitor of PDH [10,11]. The two separate activities are resolvable by ethanol treatment, the activator being ethanol insoluble and the inhibitor being ethanol soluble [10].…”

“…The two separate activities are resolvable by ethanol treatment, the activator being ethanol insoluble and the inhibitor being ethanol soluble [10]. Therefore, 100 m l aliquots of the pH 2.0 IPG were lyophilized, and extracted twice with 1 ml absolute ethanol.…”

Insulin-stimulating protein from human plasma. Chemical characteristics and biological activity

“…These enzymes include pyruvate dehydrogenase [12 -151, CAMP-dependent protein lunase [16], glycogen synthase [16], acetyl-CoA carboxylase 1171, adenylate cyclase [18], low-K,,, phosphodiesterase [19, 201 and CaZ +/MgZ +-ATPase [21]. However, the nature of the insulin mediator(s) is poorly understood.…”