Concomitant findings of isopropanol and acetone in biospecimens of decedents known not to have been exposed to the alcohol prompted a study to explain its origins. Mixtures of acetone, ADH, and NADH at pHs 7.3 and 8.8 were incubated at 37 degrees C for varying intervals. Reaction products were then analyzed by headspace GC and assured identification made by GC/MS. It was found that isopropanol is produced by reduction of acetone at pH 7.3 (to a lesser extent at pH 8.8), providing evidence for an alternate metabolic route for acetone. A mechanism for this reduction is proposed. Ranges for isopropanol (in mg/dL or mg/100 g) found in unexposed decedents were: blood 1-29; liver 7-59; brain 2-12; kidney 6-26. Thus, the forensic investigator must interpret isopropanol results cautiously, particularly when low concentrations are found.

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Hyperinsulinism, insulin resistance, and decreased number of insulin receptors are characteristic of obesity in both humans and experimental animals. To assess the role of insulin in developing obesity, diazoxide (DZ), an inhibitor of glucose-stimulated insulin secretion, was administered for 8 weeks to 7-week-old female Zucker rats in two concentrations, 50 mg/kg.day (LD-DZ), and 100 mg/kg.day (HD-DZ). The obese and lean rats were divided into three subgroups: diazoxide (DZ), pair-fed (PF), and control (C) groups (n = 6 rats/subgroup-genotype). Diazoxide-treated obese and lean animals showed significantly lower postabsorptive plasma insulin concentrations (P < 0.005) than their respective obese and lean PF and C subgroups. HD-DZ obese rats consumed more calories (P < 0.001), yet gained less weight (P < 0.05) than PF and C rats. The plasma glucose concentrations in the postabsorptive state and during glucose tolerance tests in HD-DZ obese rats were significantly lower than those in PF and C rats (P < 0.01) despite a decrease in their plasma insulin concentrations (P < 0.01), whereas HD-DZ lean rats displayed a diabetic response (P < 0.01). The adipocyte-specific insulin receptor binding was dose-dependently increased in both lean and obese DZ animals (P < 0.01). DZ had a dual effect on insulin metabolism; it decreased insulin secretion and increased insulin receptor binding. This dual effect was associated with improved glucose tolerance and a decrease in weight gain in obese rats.

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In crude receptor preparations (either particulate or soluble) of rat liver membranes, the insulin receptor exhibits complicated binding kinetics (two binding plateaus, half-saturated at approximately 60 pM and 700 pM insulin) and an apparent chromatographic heterogeneity, suggested by the presence of two detectable, soluble insulin-binding components with apparent Stokes radii of 72 A and 38 A. In contrast, the insulin receptor isolated by affinity chromatography exhibits a simple binding isotherm (half-maximal saturation of binding at 700 pM insulin) without evidence for negative cooperativity and behaves as a single component (apparent Stokes radius of 38 A) upon chromatography on Sepharose 6B. The apparent discrepancies between the properties of the unpurified insulin receptor and the affinity-purified receptor can be attributed to the presence in crude preparations of a nonreceptor constituent(s) having properties consistent with those of a membrane glycoprotein. A glycoprotein fraction from such crude soluble membrane preparations, freed from insulin receptor and subsequently partially purified using concanavalin-A-agarose, when combined with affinity-purified insulin receptor, causes both a reappearance of the complicated binding kinetics and an increase in the receptor's apparent Stokes radius from 38 having properties consistent with those of a membrane glycoprotein. MATERIALS AND METHODSPreparation of Soluble Insulin Receptor. Membranes were prepared from male CD-1 albino rats (100-140 g) as described (9) and were extracted,(5 mg of membrane protein per ml of buffer) for 1 hr at 40 with 2% (vol/vol) Triton X-100 in a calcium-free phosphate buffer, pH 7.5, containing: 130 mM NaCl, 5 mM KCI, 1.3 mM MgSO4-7 H20, and 8.6 mM Na2HPO4.After dialysis for 18 hr at 40 against the same buffer containing 0.1% (vol/vol) Triton X-100 (PT buffer), extracts were centrifuged at 150,000 X g for 60 min and the resulting supernatant was used as the source of the soluble insulin receptor. Subsequent experiments with soluble receptor were routinely done in PT buffer. Further purification of the insulin receptor was accomplished by affinity chromatography on insulin/succinyldiaminodipropylamino-Sepharose 4B (0.28 mg of insulin per ml of packed gel) prepared as described (derivative C in ref. 10) and washed with eluting buffer before regeneration with PT buffer. Receptor was eluted with an eluting buffer (0.05 M sodium acetate, pH 6.0/4 M urea/0.1% Triton X-100 in 1 ml fractions which were usually diluted immediately with 1 ml of 0.1 M sodium phosphate, pH 7.0. Insulin-binding fractions were pooled and immediately dialyzed against PT buffer for 18 hrs at 4°. The measurement of the specific binding by both soluble and particulate material of 125I-labeled insulin ug) as well as the preparation of 125I-insulin have been described in detail (1,11). Soluble receptor was measured by using polyethylene glycol [carbowax 6000; firnal conc. 10.4% (wt/vol)] to precipitate the hormone-receptor complex, as described (1). Calci...

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This study compares the receptor for insulin in rat adipocytes with an insulin receptor from transformed AL/N mouse embryo fibroblasts (SVS AL/N). In many respects the receptors from the two tissue sources are very similar. Crude solubilized receptor preparations from both fat cells and SVS AL/N cells exhibit complicated insulin-binding kinetics (two binding plateaus) as well as an apparent chromatographic heterogeneity (Sepharose 6B); each receptor preparation yields two insulin-binding components having apparent Stokes radii of about 7.2 and 3.8 nm. In contrast, the receptors isolated from both cell types by affinity chromatography behave as single chromatographic components (Sepharose 6B) having apparent stokes radii of 3.8 nm and exhibit simple insulin-binding kinetics without evidence for receptor–ligand co-operativity. The isolated receptor from SVS AL/N cells (KD about 1.2 nM) possesses a slightly lower insulin affinity than does the receptor from fat cells (KD about 0.8 nM); nonetheless, the SVS AL/N receptor exhibits an appropriate ligand specificity for insulin and insulin analogues. Receptors from both cell types are similarly sensitive to trypsin and exhibit an identical dependence on pH for insulin binding. Differences in the two receptor preparations are observed in the effect of NaCl and phospholipase C, reagents which augment insulin binding in adipocyte membranes but do not affect the binding by SVS AL/N cell membranes. Additionally, iodoacetamide, N-ethylmaleimide, and ethanol markedly reduce the binding by SVS AL/N membranes, whereas the binding by adipocyte membranes is unaffected. It is concluded that certain differences between the receptors from the two sources may be attributed to differences in the membrane environment in which the receptors reside. However, in view of the many similarities between the two receptor preparations, it is suggested that the same receptor macromolecule may participate in the response of a variety of cell types not only to insulin but also to other insulin-like polypeptides.