George C. Gerritsen

Effect of a New Hypoglycemic Agent, 3,5-Dimethylpyrazole, on Carbohydrate and Free Fatty Acid Metabolism

As a hypoglycemic agent, 3,5-dimethylpyrazole (U-6245) was found to be fifty-four times more potent orally than tolbutamide in glucose-injected, fasted intact rats. U-6245 increased glucose oxidation by intact rats. It lowered plasma free fatty acids but not blood sugar of eviscerate rats and was effective in decreasing the fasting bloodsugar levels of alloxan-diabetic rats which were unresponsive to tolbutamide. U-6245 markedly depressed plasma FFA fifteen minutes to three hours after its administration. The mechanism of hypoglycemic activity of 3,5-dimethylpyrazole is not the same as insulin, sulfonylureas or biguanides in that: (1) It is ineffective in lowering the blood sugar of eviscerates while insulin is. (2) U-6245 is active in alloxan diabetic rats which are unresponsive to tolbutamide. (3) The pyrazole increases glucose oxidation and biguanides do not. Although the mechanism of action of 3,5-dimethylpyrazole is not understood, data are presented which support the hypothesis that its action may depend on its effect on plasma FFA and also on the presence of the liver and/or intestinal tract. Since the pyrazole increases glucose oxidation in intact rats, it appears that at least part of its action may be due to the stimulation of glucose oxidation by the intestinal tract and/or liver.

The Chinese Hamster as a Model for the Study of Diabetes Mellitus

Selection for and against diabetes and subsequent inbreeding of Chinese hamsters started in 1963. Currently there are six inbred sublines that have greater than 85% incidence of glycosuria and two control inbred nondiabetic sublines that are essentially free of glycosuria. At birth, hamsters from inbred sublines are considered prediabetic. There is phenotypic variation between diabetic sublines. Onset time, incidence of ketonuria, blood glucose, plasma insulin, glucagon and glycohydrolase levels vary from subline to subline, but pancreatic insulin and glucagon levels are consistently low and high, respectively, in all diabetic sublines compared with nondiabetics. Experimental breeding data suggest a minimum of two homozygous recessive genes for diabetes. It is not known if the inbred lines are similar diabetic genotypes, but the probability is high that modifier background genes vary from subline to subline. Chinese hamsters have diabetes ranging from mild to severe. Animals weighing 25 g can excrete up to 75 ml of urine containing 3 g of glucose per day. Fasting blood glucose as high as 500 mg/dl and 10 μmol/ml of beta-hydroxybutyrate have been reported. Gluconeogenesis is elevated, and some glycolytic enzymes are decreased in severe diabetes. Low levels of renal acid glycohydrolase enzymes may contribute to glomerular capillary loop basement membrane thickening in diabetic hamsters. Caloric restriction per se or reduction of dietary fat prevented onset of hyperglycemia and hyperinsulinemia in prediabetics. Morphologic changes have been observed in pancreatic islets, kidney, nerve, blood vessels, eyes, brain, and genitourinary systems of diabetic Chinese hamsters. Pathogenesis of diabetes in this animal appears to be related to an increased demand for insulin. Initially there is a positive response to this demand by beta cells, but exhaustion occurs. This is followed by a decrease in beta-cell mass and relative or absolute insulin deficiency.

Metabolic and Underlying Causes of Diabetes Mellitus

It is emphasized that animai models should be used to study specific genotypic or phenotypic expressions associated with diabetes rather than assuming a single animal model can reflect diverse forms of the human disease. Diabetic and normal animals are reviewed on the basis of their usefulness as models of genetic, viral, and chemically induced diabetes, including the often associated immune phenomena. Characteristics of spontaneously diabetic animals with and without obesity are also described with an emphasis on both genetics and metabolic derangements. Recommendations for future animal experimentation include: more longitudinal studies evaluating the role of sex, prenatal environment, diet, and viral or chemical attack on B-cell function; characterization of the immune phenomena associated with B-cell lesions (and insulitis) in diabetic and immunologically incompetent lines; clarification of relationships between obesity and islet-ceil function with emphasis on the role of fuel metabolism, vitamins, and minerals; and, finally, the development of new models with specific genetic aberrations placed in normal or diabetic lines.

Aging Changes in Intervertebral Discs and Spondylosis in Chinese Hamsters

Vertebrae and intervertebral discs of Chinese hamsters, a species of rodents that develop spontaneous diabetes, were investigated for age-linked changes and for the occurrence of spondylosis. Aging changes in the intervertebral discs were similar in diabetic and nondiabetic animals. The incidence of spondylosis was significantly increased and its onset was accelerated in the diabetic animals. The mechanisms operative in the pathogenesis of the lesions and their relation to the human disease are discussed.

Effects of 5-Carboxy-3-Methylisoxazole on Carbohydrate and Fat Metabolism

Summary U-10387 (S-carboxy-3-methyl-isoxazole) was shown to increase glucose-1-C14 oxidation and depress release of FFA by adipose tissue in vitro and depress blood sugar of eviscerate rats. Since 3,5-dimethylisoxazole was inactive on these parameters but did lower FFA and blood sugar of intact rats, it was suggested that the activity of the 3,5-dimethyl compound was due to metabolism to the 5-carboxy derivative. Both compounds were equipotent in the intact animal in lowering FFA and blood sugar. Activities of 5-carboxy-3-methylisoxazole on the fat pad and eviscerate rats are effects similar to those exhibited by insulin.

Development of Tachyphylaxis to the Antilipolytic, Hypoglycemic Agent, 5-Methylpyrazole-3-carboxylic Acid, U-19425.

Summary After 4 days of treatment with U-19425, rats no longer respond to the drug with a decrease in plasma FFA and blood sugar 2 hours after treatment. The initial plasma FFA response to the drug is similar, but pretreated rats escape from antilipolytic effects of U-19425 faster than nonpretreated controls. Tachyphylaxis to 5-methylpyrazole-3-carboxylic acid may be due to a physiological compensatory mechanism which is mediated by the adrenal and/or pituitary glands.