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.

[Discovery and development of tamsulosin hydrochloride, a new alpha 1-adrenoceptor antagonist].

Benign prostatic hyperplasia (BPH) is an age-related disorder characterized by urinary outlet obstruction. This obstruction is due to both mechanical compression of the urethra by the hypertrophied prostate and to functional contraction of the prostate and urethra by sympathetic stimulation. We invented a novel compound tamsulosin hydrochloride, a sulphamoylphenethylamine derivative which possesses potent and selective alpha a-antagonism, and showed that this compound selectively reduced the intra-urethral pressure in the prostatic segment of the urethra in vivo. We also found that the alpha 1-adrenoceptor plays an important functional role in the prostate and urethra. For clinical use, a control release formulation was developed. This formulation did not induce orthostatic hypotension and could be administered at a fixed dose. A placebo-controlled double-blind dose finding study resulted in 0.2 mg/d as the optimal dose. This formulation significantly improved urinary outlet obstruction without affecting blood pressure as compared with placebo in P-III study, and was approved in 1993 for use in the treatment of bladder outlet obstruction associated with BPH. Tamsulosin hydrochloride is the first alpha 1-antagonist which improves bladder outlet obstruction associated with BPH without affecting blood pressure, and the treatment can be initiated and maintained at a fixed dose. Recently, the alpha 1-adrenoceptor subtypes alpha 1A, alpha 1B and alpha 1C were identified. The alpha 1C subtype is predominant and plays an important role in the human prostate. Tamsulosin hydrochloride shows high selectivity for this subtype, further supporting the clinical findings that tamsulosin hydrochloride improves bladder outlet obstruction associated with BPH with no effect on the cardiovascular system.

Disposition and metabolism of indeloxazine hydrochloride, a cerebral activator, in rats.

1. The disposition and metabolism of indeloxazine hydrochloride ((+/-)-2-[(inden-7-yloxy)methyl]morpholine hydrochloride) were studied in male Sprague-Dawley rats. 2. After oral administration of 14C-indeloxazine hydrochloride, the plasma concentration of total radioactivity reached a maximum at 15 min and declined with an apparent half-life of 2.2 h in the first 6 h period and declined more slowly thereafter. Unchanged drug in the plasma represented 13.5%, 5.9% and 0.4% of the total radioactivity at 15 min, 1 h and 6 h respectively after administration and levels decayed with a half-life of 0.9 h. 3. After oral and i.v. administration of the labelled compound, the urinary and faecal excretion of radioactivity in 72 h were 61-65% and 31-36% of the dose, respectively. Biliary excretion in bile duct-cannulated animals amounted to 49% of the dose in 72 h. 4. Seven metabolites have been isolated from the plasma or urine and characterized by i.r., n.m.r. and mass spectrometry. They were derived through dihydrodiol formation in the indene ring, hydroxylation of the indene ring and N-acetylation, oxidation and oxidative degradation of the morpholine ring. Some metabolites were excreted as their glucuronic acid or glucose conjugates. The major metabolite appeared to the trans-indandiol analogue of indeloxazine. 5. Possible metabolic pathways of degradation of the morpholine ring are discussed.

New sulfamoylphenethylamines, potent alpha 1-adrenoceptor antagonists.

The (+)-isomer of amosulalol, a combined alpha- and beta-adrenoceptor antagonist, was one log unit order more potent and less potent than the (-)-isomer in blocking alpha 1- and beta 1-adrenoceptors, respectively, in anaesthetized rats. Nine newly synthesized desoxy compounds derived from amosulalol and its analogues were found to possess potent alpha 1-adrenoceptor blocking activity and to be practically devoid of beta 1-adrenoceptor blocking activity. Among the desoxy derivatives, YM-12617 was more potent than prazosin in blocking alpha 1-adrenoceptors in anaesthetized rats and in reducing blood pressure, total peripheral resistance and left ventricular work in anaesthetized dogs.