Biotin enhances glucose-stimulated insulin secretion in the isolated perfused pancreas of the rat.

The effects of biotin on insulin secretion in pair-fed control rats and biotin-deficient rats were investigated using the method of isolated pancreas perfusion. Isolated pancreas perfusion was performed using 20 mM glucose, 10 mM arginine, and 20 mM glucose plus various concentrations of biotin (20 mM glucose + biotin solution) as stimulants of insulin secretion. The insulin response to 20 mM glucose in biotin-deficient rats was approximately 22% of that seen in control rats. The level of the insulin response to 10 mM arginine was also significantly lower in biotin-deficient rats than in control rats. These results indicate that insulin release from the pancreas was disturbed in biotin-deficient rats. The insulin responses to 20 mM glucose + 1 mM biotin in biotin-deficient and control rats increased to 165% and 185%, respectively, of that to 20 mM glucose. These biotin-induced increases in glucose-stimulated insulin release were evident within the first few minutes of the infusion. An enhancement of the arginine-induced insulin response in control rats was not found when arginine and biotin was administered. These results suggest that biotin may play an important role in the mechanism by which glucose stimulates insulin secretion from the beta cells of the pancreatic islets.

A high biotin diet improves the impaired glucose tolerance of long-term spontaneously hyperglycemic rats with non-insulin-dependent diabetes mellitus.

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat, serving as a spontaneously diabetic model with non-insulin-dependent diabetes mellitus (NIDDM), exhibits impaired glucose tolerance (IGT) at about 16 weeks of age. In this study, we investigated whether or not biotin, a water-soluble vitamin, improved the IGT of OLETF rats. To this end, we administered diets containing one of three levels of biotin, a high-biotin diet (BH), a normal-biotin diet (BN) and a basal-biotin diet (BB), to OLETF rats up to 24 weeks of age. An oral glucose tolerance test (OGTT) was performed four times between 13 and 22 weeks of age. The administration of a BH corrected the IGT of OLETF rats. Upon further investigation, we found that insulin secretion in the OLETF-BH rats was decreased to a significant extent, signaling that the hyperinsulinemia typical to the OLETF-BH rats had clearly improved. Body weights were significantly lower in the OLETF-BH group than in the other OLETF groups, even though the OLETF-BH rats showed a significantly higher average daily food intake. The body weight gain of the OLETF-BH rats followed the same tendency as the control-LETO (Long Evans Tokushima Otsuka) rats (LETO-BB and LETO-BN). These results demonstrate that a high-level biotin diet can improve the glucose handicap in NIDDM rats.

Biochemical consequences of biotin deficiency in osteogenic disorder shionogi rats.

The biological consequences of biotin deficiency in rats were investigated using osteogenic disorder Shionogi rats which have a hereditary defect in ascorbic acid synthesizing ability. Decrease of liver ascorbic acid content and fasting plasma glucose and an increase of plasma non-esterified fatty acid (NEFA) appeared in biotin deficient rats fed a diet containing 200 mg ascorbic acid per 100 g diet, compared with the pair fed control. On the other hand, in the case of rats fed a diet containing 500 mg ascorbic acid, although the clinical features of biotin deficiency developed, the ascorbic acid contents of liver and adrenal gland increased in comparison with those of AsA 200 mg groups, and the alterations of plasma levels of glucose and NEFA were improved partially in glucose and greatly in NEFA, respectively. This suggests that ascorbic acid may be consumed in the improvement of the metabolic impairments induced by biotin deficiency.

Effect of pindolol, a beta-adrenoceptor blocking agent, on lipid metabolism.

Pindolol, a beta-adrenoceptor blocking agent, was administered to rats to determine the effects of the drug on lipid and lipoprotein in plasma and tissues. The drug caused significant reductions in plasma triglyceride, free fatty acid and very low density lipoprotein. As for lipoprotein lipase activity, the drug produced varying effects; an increase in the heart and a reduction in the adipose tissue. No significant changes in plasma cholesterol, low density lipoprotein and high density lipoprotein cholesterol were observed. The disturbance of growth was noted following pindolol treatment.

Formation of a vasopressor substance in the incubated serum of patients with various hypertensive diseases.

A vasoactive substance was produced in serum when incubated at 37 degrees C. This substance differed from other known vasoactive agents. It was a phospholipid and caused an elevation in blood pressure by its direct vasoconstriction. This pressor substance increased in the incubated sera of patients with essential hypertension and in spontaneously hypertensive rats. But it was significantly low in humans and dogs in anephric states. These results suggest that the pressor substance participates in the pressor mechanism of essential hypertension and its production is closely related to the kidney.

Carnitine depletion as a probable cause of hyperlipidemia in uremic patients on maintenance hemodialysis.

The mechanism of te development of hemodialysis hyperlipidemia was investigated in uremic patients on maintenance hemodialysis. Hemodialysis treatment lost large amounts of carnitine from blood into the dialysate fluid, resulting in the reduction in serum concentration of carnitine. After the treatments were repeated for more than 12 months, the serum concentration of carnitine reduced markedly and the serum triglyceride level increased significantly. In contrast, in patients who had been supplemented with commercial amino acids solution, the serum concentrations of carnitine and lipid were within normal ranges and remained unchanged even after repeated hemodialysis treatments. Carnitine administration also reduced the serum triglyceride level to or towards normal. The results suggest that carnitine depletion induced by hemodialysis treatments has a probable causal relationship to hyperlipidemia in uremic patients on long-term maintenance hemodialysis and that supplementation of carnitine or amino acids prevents carnitine depletion and improves hemodialysis hyperlipidemia.

Effect of aging on lipid and carnitine metabolism.

In healthy subjects aged 20 to 50 years, the urinary excretion of carnitine and its serum concentration increased rapidly and markedly after synthetic beta 1-24 ACTH-Z was injected. Their serum triglyceride levels changed inversely. In contrast, healthy subjects older than 70 and patients aged 45 to 50 with atherosclerosis exhibited lower and delayed changes of carnitine excretion and serum concentrations of carnitine and lipid after ACTH injection. When the aged subjects and the atherosclerotic patients were administered with triiodothyronine prior to ACTH, their metabolic responses to ACTH improved towards normal. The results suggest that the aging process impairs the homeostatic regulation of serum lipid through a "lipid-carnitine" system and that thyroid hormone plays a contributory role in the activation of this system.

Lipid-lowering effect of carnitine in patients with type-IV hyperlipoproteinaemia.

Serum-lipid concentrations were determined in patients with type-IV hyperlipoproteinaemia treated with 900 mg/day oral DL-carnitine chloride. Serum-triglyceride was significantly reduced and concentrations continued to decline as carnitine administration continued. Total and esterified cholesterol concentrations did not change. Intravenous infusion of carnitine produced the same effects. The results suggest that carnitine is of value in the therapy of type-IV hyperliproteinaemia. Increased oxidation of free fatty acids in the tissues seems to account for the effects of carnitine on serum-lipid concentrations.

Urinary excretion of carnitine in patients with hyperthyroidism and hypothyroidism: augmentation by thyroid hormone.

Urinary excretion of carnitine and serum concentrations of carnitine, triglyceride, and free fatty acids were measured in 54 hyperthyroid and 13 hypothyroid patients, and the results were compared with those of normal subjects. In hyperthyroid patients urinary excretion of carnitine was highly increased above that of the control subjects. On adequate treatment with antithyroid drug, carnitine excretion was reduced to the normal range, and serum lipids changed in parallel. In contrast, carnitine excretion was markedly reduced in hypothyroid patients. After substitution therapy with thyroid hormones the excretion increased in these patients. This change was associated with a marked reduction of serum triglyceride. There was an inverse correlation between urinary excretion of carnitine and serum triglyceride concentration. Carnitine excretion was significantly correlated with serum thyroxine concentration in hyper- and hypothyroid patients. The results suggest that thyroid hormones play an important role in carnitine metabolism, which in turn influences serum triglyceride metabolism.

Urinary excretion of carnitine in man.

A convenient assay procedure for urinary carnitine is described. Urinary excretion of carnitine is determined in human subjects in various experimental states. Average excretions by this procedure were 59.3+/-3.3 mg. per day in men and 44.1+/-2.9 mg. per day in women. Carnitine excretion had a wide variation in women during the menstrual cycle and reached a maximum at the time of ovulation, but the excretion was relatively constant in men. Marked increases in carnitine excretion were observed in the states with increased lipolysis induced by fasting or ACTH injection. This finding suggests that lipid mobilization might be reflected in the excretion of carnitine in urine.

Separation and determination of carnitine and its esters in human serum.

A colorimetric method for the determination of carnitine and its derivatives is described. Free carnitine, acetylcarnitine and palmitoylcarnitine were extracted with chloroform-methanol. After evaporation, the residue was dissolved in n-butanol and water; palmitoylcarnitine in the organic phase, and free carnitine and acetylcarnitine by passing the aqueous phase through a column of Amberlite CG-120 (H+). Separated carnitine derivatives were hydrolyzed to free carnitine which was followed by the Amberlite column chromatography. After eluting with 2N NH4OH solution, the samples were esterified and determined colorimetrically.