John C. Kapeghian

Determination of Ascorbic Acid and Dehydroascorbic Acid in Blood Plasma Samples

Abstract Following the stabilization of the plasma samples with HClO4 and EDTA, the samples could be directly analyzed by HPLC using electrochemical detection and reversed-phase columns. The accuracy and precision of the method was evaluated using plasma samples spiked with ascorbic acid (10 μg/ml) and the results were also compared to the classical colorimetric procedure. Dehydroascorbic (5 μg/ml) was determined in plasma samples using UV detection following derivatization at room temperature for 45 minutes with o-phenylenediamine.

Selected physical and biochemical parameters in the streptozotocin-treated guinea pig: insights into the diabetic guinea pig model.

Since evidence suggests that ascorbic acid deficits may provoke certain diabetic complications, it becomes necessary to develop a diabetic animal model which, like man, is unable to synthesize this vitamin. To this end, the present study monitored the diabetogenic effects of streptozotocin (STZ, 150 mg/kg) in the male guinea pig, a species rarely used in diabetes research. Over a 3-week period, body weight and relative food intake were lower in the STZ group compared to controls. The mean daily water intake and urine volume of the STZ group after 1 week were 175 and 270% of their initial pretreatment values, respectively, while control values were unchanged. The STZ group also exhibited a persistent glycosuria throughout the study. At the end of 3 weeks, aldehyde fuchsin staining of pancreatic beta cell granules (an index of stored insulin) was 58% lower in the STZ group compared to controls. Plasma C-peptide (indicator of insulin secretion) was expressed in human equivalents (mean +/- SEM). C-peptide was reduced in the STZ group (103 +/- 65 pg/ml) compared to controls (549 +/- 96 pg/ml); however, no change in plasma glucose was observed. Plasma ascorbic acid levels also were lower for STZ animals (150 +/- 26 micrograms%) versus controls (410 +/- 28 micrograms%). This study 1) demonstrates a diabetic syndrome in the STZ-treated guinea pig based on a reduced growth rate, beta cell dysfunction, polydipsia, polyuria and glycosuria, and 2) suggests the usefulness of this diabetic model in studies of pathologic mechanisms influenced by ascorbic acid.

Effects of streptozotocin in the male guinea pig: A potential animal model for studying diabetes

The effects of acutely administered streptozotocin in the male guinea pig were studied for a period of 18 days following treatment. A single intracardiac injection of streptozotocin (150 mg/kg) was administered on Day 0. On Day 2, plasma glucose concentrations were not significantly different from control levels. On Day 7 and 18, an oral glucose tolerance test was performed with streptozotocin-treated animals receiving an acute injection of either insulin (18 U/kg, i.m.) or saline 90 minutes prior to glucose loading. On Day 7, streptozotocin-treated animals receiving saline had significantly elevated plasma and urine glucose concentrations at 3 hours after glucose loading when compared to controls. Streptozotocin-treated animals receiving insulin however, had significantly lower plasma glucose concentrations at 3 hours while urinary glucose was equal to control values. The second glucose tolerance test performed on Day 18 yielded similar results. Necropsies were performed on animals that died after Day 6. Lesions found in the streptozotocin-treated animals included: small and irregular pancreatic islets, pyknotic nuclei and degranulation of beta cells, renal proximal tubule swelling and vacuolization, adrenal cortical hyperplasia, hepatocyte vacuolization, and visceral fat atrophy. Animals surviving until Day 18 were sacrificed and found to have significantly elevated kidney and adrenal weights compared to controls. These changes illustrate the effectiveness of streptozotocin in the acute chemical induction of diabetes in an animal model (guinea pig) which, like humans, requires a dietary source of ascorbic acid.

Alteration of the disruptive effect of fenfluramine on food consumption in the rat by repeated post-session administration of d-amphetamine

The purpose of this study was to determine whether repeated treatment (15 days) with d-amphetamine (AMP) or fenfluramine (FEN), administered after a daily 3 h feeding session (e. g. post-session), would result in tolerance or crosstolerance to the decrement in food consumption induced by treatment with either drug before feeding (e. g. pre-session). Groups of male rats were treated IP with 0.5 ml saline, 1.0, 2.0, or 4.0 mg/kg AMP, or 2.5, 5.0, or 10.0 mg/kg FEN prior to a 3 h feeding session. For the next 15 sessions, the respective groups were treated post-session with saline (0.5 ml), AMP (4.0 mg/kg), or FEN (10 mg/kg). Following the 15 day postsession phase, each group again received this pre-session treatment. The initial pre-session treatment with all dosages of these two drugs produced a significant decrease in food consumption. Tolerance to the food intake suppressant effect of FEN, but not AMP, resulted from repeated post-session treatment with the same agent. Repeated post-session treatment with AMP resulted in a significant decrement in the suppressant activity of FEN on food intake, whereas the corresponding post-session treatments with FEN did not alter the pre-session effects of AMP, except for an enhancement seen with higher AMP doses.

Effects of ammonia on selected hepatic microsomal enzyme activity in mice

Atmospheric ammonia (NH/sub 3/) is produced by a number of industrial sources however it is the biological action of urease-containing bacteria upon urine and fecal waste products that is responsible for producing NH/sub 3/ in laboratory animal facilities. Since NH/sub 3/ is a primary irritant, studies emphasizing the pulmonary toxicity of both acute and repeated exposures have appeared. Since the mouse has proven to be a sensitive animal model for use in NH/sub 3/ toxicity studies and work in the rat has produced only minimal microsomal changes, the present study was undertaken to determine whether acute or repeated exposure to NH/sub 3/ gas inhibits selected microsomal enzyme activity in the mouse.

A compact multichamber gas inhalation exposure system for mice.

A multi-unit, dynamic flow, inhalation exposure system which is capable of accommodating 12 mice per unit has been described. Components of the system include a mixing board, one or more glass distributing tubes, and detachable glass chamber tubes. The flow of a specified concentration of test gas exits from the mixing board, enters a distributing tube, and is then distributed equally to 12 chamber tubes housing one mouse each. Advantages includes quick equilibration time (10 min), relatively low flow rates (20 l/min per distributing tube), ease of disassembly for cleaning, compact size, modest expense and minimal temperature, pressure and physico-chemical effects.