Glyceride metabolism in the myopathic hamster

Lipogenic potential of liver from morbidly obese patients with and without non-insulin-dependent diabetes

Intra-abdominal liver biopsies were obtained during surgery from fasted obese patients with non-insulin-dependent diabetes mellitus (NIDDM), obese normoglycemic controls, and lean controls. Lipid synthesis was studied in freshly isolated hepatocytes and liver homogenates from the three groups of subjects. Incorporation of 3H2O into the lipids of hepatocytes was determined in the absence and presence of insulin (0.1 mumol/L). The activities of five enzymes involved in fatty acid synthesis, and the incorporation of 14C-glycerol-3-phosphate into lipids were determined in liver homogenates. Basal lipid synthesis by hepatocytes was not different in the three groups of patients. Insulin stimulated lipogenesis by 8% +/- 30% in the lean controls, 33% +/- 8% in the obese controls and 17% +/- 6% in the NIDDM patients. No significant differences in the activities of the five enzymes that are involved in de novo fatty acid synthesis among the three groups of patients were observed. Similarly, incorporation of 14C-glycerol-3-phosphate by liver homogenates, in the presence of saturating or submaximal concentrations of fatty acids, did not differ among the three groups. These results show that under the experimental conditions of this study, including the fasted state of the patients, the basal capacity of liver of NIDDM patients to synthesize fatty acids or glycerides is the same as that of liver from obese and lean controls. Thus, it is likely that an increase in fatty acid flux into a liver with normal lipogenic potential may contribute to the increased synthesis of triglycerides by the liver of these patients in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of exercise on lipogenic enzyme activity and glyceride synthesis by liver homogenates of diabetic rats

The purpose of this study was to determine if exercise ameliorates the elevated levels of triglycerides in diabetic rats and also to determine if the capacity of liver to synthesize glycerides correlates with changes in plasma triglyceride levels. Forty female rats were divided into four groups: sedentary control, sedentary diabetic, exercised control, and exercised diabetic. Diabetes was induced by intravenous injection of alloxan (40 mg/kg), and control rats were sham-dosed with physiologic saline. All rats remained sedentary in their cages for the first week after the injections. The exercised groups were exercised for seven consecutive days for 2 h/d at 20 m/min (0 grade). All rats were killed 24 hours after the last exercise bout. Blood glucose levels were significantly higher in the diabetic group than the nondiabetic counterparts, but exercise did not affect glucose levels in either the diabetic or nondiabetic groups. Exercise, however, significantly lowered plasma triglyceride and free fatty acid levels in both diabetic and nondiabetic rats. The activities of the five enzymes involved in fatty acid synthesis were all depressed in the diabetic rats compared to controls, and exercise had no effect on the activities of the enzymes. The capacity of liver to synthesize total lipids, diglycerides, or triglycerides was not different in the diabetic rats from that of nondiabetic rats, and exercise did not change that. Only phospholipid synthesis from glycerol-3-phosphate was affected by diabetes. It is concluded that exercise ameliorates the elevations in plasma triglyceride levels that result from diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)

Disorders of lipid metabolism in muscle

At rest and during sustained exercise, lipids are the main source of energy for muscle. Free fatty acids become available to muscle from plasma free fatty acids and triglycerides, and from intracellular triglycride lipid droplets. Transport of long-chain fatty acyl groups into the mitochondria requires esterification and de-esterification with carnitine by the "twin" enzymes carnitine palmityltransferase (CPT) I and II, bound to the outer and inner faces of the inner mitochondrial membrane. Carnitine deficiency occurs in two clinical syndromes. (1) In the myopathic form, there is weakness; muscle biopsy shows excessive accumulation of lipid droplets; and the carnitine concentration is markedly decreased in muscle but normal in plasma. (2) In the systemic form, there are weakness and recurrent episodes of hepatic encephalopathy; muscle biopsy shows lipid storage; and the carnitine concentration is decreased in muscle, liver, and plasma. The etiology of carnitine deficiency is not known in either the myopathic or the systemic form, but administration of carnitine or corticosteroids has been beneficial in some patients. "Secondary" carnitine deficiency may occur in patients with malnutrition, liver disease, chronic hemodialysis, and, possibly, mitochondrial disorders. CPT deficiency causes recurrent myoglobinuria, usually precipitated by prolonged exercise or fasting. Muscle biopsy may be normal or show varying degrees of lipid storage. Genetic transmission is probably autosomal recessive, but the great male predominance (20/21) remains unexplained. In many cases, lipid storage myopathy is not accompanied by carnitine or CPT deficiency, and the biochemical error remains to be identified.

The distribution of lipoprotein lipase (clearing factor lipase) activity in the adiposal, muscular and lung tissues of ten animal species

1. The lipoprotein lipase activity of white adipose tissue from a variety of sites, muscular tissue from the heart, limb and diaphragm and lung tissue was determined in samples from nine mammalian and one avian species. 2. The effect of 24 hr starvation on these activities was studied in five of the mammalian and the avian species.