Role of plasma insulin concentration in regulating glucose and lipid metabolism in lean and obese Zucker rats.

OBJECTIVE: To determine the role of plasma insulin concentration in regulating glucose and lipid metabolism in insulin-resistant obese Zucker rats and to compare obese rats with lean controls with respect to changes in insulin sensitivity. DESIGN: Animal study of lean and obese rats with or without insulin sensitizer, YM268. ANIMALS: Nine week old male lean (Fa/-) and obese (fa/fa) Zucker rats. MEASUREMENTS: Plasma glucose, insulin, triglyceride (TG), non-esterified fatty acid (NEFA), cholesterol at baseline and after 14 d, the dose of YM268 for exhibiting a 30% decrease in each parameter (ED30). RESULTS: Insulin, TG, and NEFA concentrations were approximately 2-6 times higher in obese rats. YM268 had no effect on glucose but decreased insulin in lean and obese rats with ED30 of 3.0 and 2.9 mg/kg. YM268 also reduced TG and NEFA in lean and obese rats (ED30 (mg/kg): lean; 4.1 (TG), 5.0 (NEFA), obese; 2.1, 3.0]. A significant correlation of either TG or NEFA level to insulin was established in lean and obese rats. CONCLUSION: Plasma TG and NEFA, but not cholesterol concentration, are dependent on plasma insulin in lean and obese Zucker rats, and insulin sensitivity with respect to TG and NEFA metabolism in obese rats may not be different from that in lean rats.

Insulin sensitizer YM268 ameliorates insulin resistance by normalizing the decreased content of GLUT4 in adipose tissue of obese Zucker rats.

Genetically obese Zucker rats exhibit mild hyperglycaemia and hyperinsulinaemia suggesting the existence of peripheral insulin resistance. We have examined the effects of YM268, an analogue of thiazolidinedione, on the content and translocation of a glucose transporter (GLUT4) in epididymal adipose tissue in 11-week-old obese and lean Zucker rats. The administration of YM268 at a dose of 10 mg/kg for 2 weeks ameliorated hyperglycaemia, hyperinsulinaemia, and impaired glucose tolerance after glucose load in obese rats. The GLUT4 content per fat pad in obese rats was reduced to 36% of that in lean littermates. Obese rats treated with YM268 increased GLUT4 concentrations in their fat pads from a basal value of 36% up to 191% of the level in lean rats. Furthermore, in adipocytes prepared from obese rats, an increase in the ratio of GLUT4 in plasma membrane to the total amount of GLUT4 (PM-GLUT4 ratio) induced by the submaximal concentration of insulin (0.3 nmol/l) was significantly attenuated compared with that in lean rats. But the maximum effect of insulin (3 nmol/l) was not attenuated. Meanwhile, YM268 had no significant effect on the attenuated PM-GLUT4 ratio in response to insulin in obese rats. These data suggested that one of the mechanisms by which YM268 improved insulin resistance in obese Zucker rats was to normalize the decreased GLUT4 content in the adipose tissue.

Effects of acylcarnitine-transferase inhibitors on adenine nucleotide metabolism and ischemic tissue injury in isolated perfused rat heart.

The ability of irreversible acylcarnitine-transferase inhibitors, sodium 2[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate (POCA) and 2-tetradecyl-glycidic acid (TDGA), to reduce myocardial ischemic injury was studied in Langendorff-perfused hearts exposed to ischemia (zero mmHg) followed by aerobic reperfusion (60 mmHg). Rat hearts were pretreated with either POCA (15 mg/kg) or TDGA (5 mg/kg) s.c. 120 min before the perfusion. Treated hearts showed a decreased release of creatine kinase and lactate on reperfusion after 30 min ischemia. POCA-treated hearts showed significantly higher ATP concentrations than control hearts on reperfusion. POCA also improved the maximum recovery of the pressure-rate product but with a significant delay. During the ischemic period, though, POCA decreased the ATP concentration at a rate three times that of controls during the first 10 min. No further reductions were observed for up to 30 min of ischemia. TDGA also showed a reduction of ATP. Thus, the observation that POCA stimulated ATP synthesis and reduced creatine kinase release on reperfusion after ischemia suggests that this agent provides some protection to the ischemic myocardium. However, during ischemia, it is likely that the depletion of ATP concentration induced by POCA resulted in delayed recovery of mechanical function on reperfusion.

Effects of nicardipine on ischemic mechanical failure and tissue injury in isolated perfused rat heart.

Using a Langendorff rat heart preparation, we examined effects of nicardipine, a calcium channel blocker, on different stages of ischemic damage, characterized by a development of contracture and leakage of intracellular enzymes. Maximum recoveries of heart rate (HR) and peak left ventricular pressure-HR product after 20 min ischemia were attenuated by about 25% compared with those before ischemia. When nicardipine (0.1 mumol) was added to the perfusate 5 min prior to ischemia, this mechanical failure recovered completely to the pre-ischemic level. Although a significant increase in left ventricular end-diastolic pressure was observed in hearts exposed to 30 min ischemia, the amount of creatine kinase (CK) released during re-flow after 30 min ischemia was not enhanced by contracture but was proportional to the duration of ischemia (compared with that of 20 min ischemia). Nicardipine reduced CK leakage by 25% after 30 min ischemia but did not alter either ATP levels or coronary flow. The beneficial effects of nicardipine on ischemic damage are probably related to inhibition of calcium influx (Terai et al: Biochem Pharmacol 30: 375, 1981), which may accompany reperfusion of ischemic myocardium.

Selective binding of YM-09151-2, a new potent neuroleptic, to D2-dopaminergic receptors.

Effects of YM-09151-2 and five other neuroleptics (haloperidol, spiperone, chlorpromazine, sulpiride and clozapine) on the binding of [3H]-ligands to nine different receptors (alpha 1-adrenergic, alpha 2-adrenergic, beta-adrenergic, muscarinic, D2-dopaminergic, H1-histaminergic, 5HT1-serotonergic, 5HT2-serotonergic and opiate receptors) and on dopamine-sensitive adenylate cyclase were determined using brain membranes in the rat, guinea-pig and dog. The affinity of YM-09151-2 for D2-receptors with a Ki value of 0.1 nM was more than 1000-times higher than that for the other receptors and dopamine-sensitive adenylate cyclase, and it was the greatest among the neuroleptics tested.

Dopamine receptor system involving adenylate cyclase in canine caudate nucleus.

Two distinct dopamine binding sites, referred to as D1 and D2, exist in canine caudate nucleus, as characterized by [3H]dopamine binding to the synaptic membrane fraction. D1 has the low affinity for dopamine with the dissociation constant of a few micromolar, whereas the affinity for D2 is about two orders of magnitude greater. Classical neuroleptics such as haloperidol and chlorpromazine have no selectivity in the inhibition of D1 and D2 binding, whereas a number of 2-methoxy benzamide derivatives which have been synthesized in our laboratories exhibit rather different selectivity. Correlation between the selectivity of those benzamide derivatives for the two sites and the inhibition of apomorphine-induced stereotypy in rats suggests that D1 is more responsible for the stereotypy. Photoaffinity labeling of D1 and D2 with [3H]dopamine demonstrates that the two sites are distinct entities. In the D1 system, the adenylate cyclase which is responsive to Gpp(NH)p can be dissociable by the treatment with GTP-Sepharose into a guanine nucleotide binding unit and a catalytic unit which is insensitive to Gpp(NH)p. The catalytic unit restores the responsiveness to Gpp(NH)p after preincubation with the nucleotide binding unit. Furthermore, endogenous cAMP-dependent phosphorylation of two particular proteins (protein Ia and Ib) is shown, which may be at least partly responsible for stereotypy and dopamine turnover in the caudate nucleus.

Neuroleptic properties of cis-N-(1-benzyl-2-methylpyrrolidin-3-yl)-5-chloro-2-methoxy-4-methylaminobenzamide (YM-09151-2) with selective antidopaminergic activity.

A new benzamide, cis-N-(1-benzyl-2-methylpyrrolidin - 3 - yl) - 5 - chloro - 2 - methoxy - 4 - methylaminobenzamide (YM-09151-2) exhibited more potent and longer-lasting inhibitory effects on apomorphine-induced behaviours (stereotyped behaviour, emesis and hypothermia), and methamphetamine-induced stereotyped behaviour, conditioned avoidance response and open field behaviour, conditioned avoidance response and open field behaviour than either structurally similar benzamides (YM-0850 and sulpiride) or classical neuroleptics [chlorpromazine (CPZ) and haloperidol(HPD)]. Such inhibitory effects of YM-09151-2 relative to cataleptogenicity were greater than those of CPz and HPD. In contrast, sulpiride elicited few of the neuroleptic effects described above. YM-09151-2, a potent inhibitor for dopamine-sensitive adenylate cyclase (Ki: 3.0 nM) reduced, in a selective manner, the binding of [3H]dopamine to the dopamine D1 receptor (Ki:4.8 nm) associated with adenylate cyclase rather than to the dopamine D2 receptor (Ki: 0.98 microM) independent of adenylate cyclase. Sulpiride, on the contrary, inhibited only the binding to the dopamine D2 receptor, CPZ and HPD antagonized [3H]dopamine nonselectively at the two distinct dopaminergic receptors. These results suggest that YM-09151-2 is a potent and long-lasting neuroleptic with a highly selective blocking action on the dopamine D1 receptor.