Ciglitazone reverses cAMP-induced post-insulin receptor resistance in rat adipocytes in vitro.

Ciglitazone (cig), a thiazolidine-dione, lowers glucose and insulin levels in animal models of diabetes type II but not in controls. Since catecholamines given to rat adipocytes in vitro induce insulin resistance similar to that seen in type II diabetes in vivo, we measured the effect of cig on mono-A14-[125I]insulin binding and 3-O-methyl-D-glucose transport (GT) in isolated rat adipocytes treated with isoprenaline (iso, 10 microM). Cig (less than or equal to 5 microM) reversed (ED50 10 nM) the inhibitory effect of iso on insulin stimulation of GT. It had no effect on either basal or insulin stimulated GT. Furthermore, cig did not influence insulin binding either in the presence or absence of iso, which indicates that cig acts only on a post-insulin receptor level. Cig also reversed the inhibition of GT by both forskolin, a cyclase activator and RO20-1724, an imidazolidine phosphodiesterase inhibitor but not that of db-cAMP. It thus seems that cig does not act within the cAMP system but only neutralizes its inhibitory effect on the insulin stimulation of GT.

Catecholamine-induced insulin resistance of glucose transport in isolated rat adipocytes.

The effects of pre-incubation with isoprenaline and noradrenaline on insulin binding and insulin stimulation of D-glucose transport in isolated rat adipocytes are reported. (1) Pre-incubation of the cells with isoprenaline (0.1-10 microM) in Krebs-Ringer-Hepes [4-(2-hydroxyethyl)-1-piperazine-ethanesulphonic acid] buffer (30 min, 37 degrees C) at D-glucose concentrations of 16 mM, in which normal ATP levels were maintained, caused a rightward-shift in sensitivity of D-glucose transport to insulin stimulation by 50% and a decrease in maximal responsiveness by 30% (2) [A14-125I]insulin binding was reduced significantly by 35% at insulin concentrations less than 100 mu-units/ml and Scatchard analysis showed that this consisted mainly of a decrease in high-affinity binding. (3) Pre-incubation with catecholamines under the same conditions but at low glucose concentrations (0-5 mM) caused a fall in intracellular ATP levels of 65 and 45% respectively. (4) The fall in ATP additionally lowered insulin binding by 50% at all insulin concentrations and a parallel shift of the binding curves in the Scatchard plot showed that this was due to a decrease in the number of receptors. (5) At low and high ATP concentrations the insulin stimulation of D-glucose transport was inhibited to a similar extent. (6) Pre-incubation with catecholamines thus inhibited insulin stimulation of D-glucose transport in rat adipocytes mainly by a decrease in high-affinity binding of insulin, which was not mediated by low ATP levels. This mechanism may play a role in the pathogenesis of catecholamine-induced insulin resistance in vivo.

Effect of the bispyridinium compounds HGG12, HGG42, and obidoxime on synaptic transmission and NAD(P)H-fluorescence in the superior cervical ganglion of the rat in vitro.

Postganglionic compound action potential (AP) and intracellular NAD(P)H-fluorescence were recorded simultaneously in the perifused superior cervical ganglion of the rat (SCG) to study the effects of the bispyridinium oximes HGG12, HGG42 and obidoxime. HGG12 and HGG42 inhibit the compound action potential (AP) (ID50: 70 microM) and the reductive part of NAD(P)H changes (ID50: 75 microM) recorded upon stimulation of the SCG, while obidoxime has no ganglion blocking effects in concentrations up to 1 mM. The effects of inhibitors of cholinergic transmission were also studied in order to understand the mechanisms of action of the oximes. Hexamethonium (C6) and atropine, competitive inhibitors of receptors of nicotinic and muscarinic cholinergic transmission respectively, were found to block synaptic transmission (C6 ID50:150 microM, atropine ID50: 70 microM) and the reductive part of the NAD(P)H response (C6 ID50: 70 microM, atropine ID50: 50 microM) in a quantitatively similar way. Comparison of the ganglionic action of HGG12 and HGG42 with that of the inhibitory agents characterises them as inhibitors of receptors of nicotinic ganglionic transmission. Furthermore at concentrations of about 10 microM, HGG12 behaves like atropine and leads to an increase in AP and reductive fluorescence response. It is therefore probable that HGG12 has in addition an affinity for ganglionic muscarinic receptors which HGG42 does not have.