Streptozotocin-induced diabetes lowers retinol-binding protein and transthyretin concentrations in rats.

Retinol-binding protein (RBP) and transthyretin (TTR) in the plasma, liver and kidney, retinol in plasma, and total vitamin A in the liver were measured in rats 6 weeks after diabetes mellitus had been induced by streptozotocin (STZ). The diabetic rats gained 83% less weight despite consuming 45% more feed than the non-diabetic controls. Plasma and kidney concentrations of RBP and TTR were significantly lower in diabetic than in the non-diabetic control rats. Unlike the retinol carrier proteins, plasma albumin concentrations remained unaffected. Plasma concentrations of retinol were decreased while its hepatic levels increased in the diabetic animals. The depressed circulatory levels of retinol may reflect an altered metabolism of its transport proteins.

Streptozotocin-induced diabetes in rats is associated with impaired metabolic availability of vitamin A (retinol).

Using streptozotocin-induced diabetic Wistar rats, studies were carried out to examine the metabolic availability of vitamin A in the plasma, liver and the retina of the eye. Control and diabetic rats were fed ad lib. on a semi-purified diet either with or without (basal) vitamin A supplementation, or pair-fed on the basal diet for 4 weeks. Despite the fact that diabetic rats consumed 48% more feed, they had lower plasma concentrations of retinol (P < 0.003). The decrease in plasma retinol concentration was a response to diabetes (or diabetes-induced trauma), since neither pair-feeding (P < 0.01) nor vitamin A supplementation altered this effect (P < 0.05). Furthermore, the hepatic concentrations of the vitamin in these animals remained elevated and this increase was greater in the supplemented diabetic group (P < 0.001). Decreases in 11-cis retinal (a component of rhodopsin) concentrations in the retina were also observed in diabetic animals. The increased hepatic and the decreased plasma and retina vitamin A levels suggest a defect in the transport of the vitamin from the liver.

Strain variation in vitamin A (retinol) status of streptozotocin-induced diabetic rats.

Decreased plasma concentrations of vitamin A (retinol) and retinol-binding protein have been previously identified in human subjects with type I diabetes mellitus. The present study was undertaken to investigate the effects of streptozotocin-induced diabetes in rats of three different strains including Wistar Furth, Sprague Dawley and Wistar, on plasma and liver concentrations of vitamin A. The diabetic animals gained less weight than nondiabetic controls even though they ate 50% more food. The hepatic vitamin A concentration was increased at three weeks after the onset of diabetes in all three strains of rats but the magnitude of increase was greater in Wistar than either Wistar Furth or Sprague Dawley rats. This increased storage of vitamin A in diabetic animals most likely is due to increased food intake. The plasma concentrations of vitamin A, on the other hand, remained unaffected in Wistar Furth and decreased moderately (P < 0.02) in Sprague Dawley but severely (P < 0.0001) in Wistar rats. The fact that the plasma vitamin A levels in diabetic Wistar and Sprague Dawley rats were markedly reduced despite their increased hepatic store suggest an impairment in the transport of vitamin A from the liver. The circulatory levels of vitamin A in Wistar rats are more sensitive to the diabetic state, which is in agreement with those observations seen in diabetic patients. Because of this similarity, it is reasonable to suggest that Wistar should be the choice of rat strain for future experimental studies involving vitamin A and diabetes relationships.

Intestinal absorption of vitamin A in streptozotocin-induced diabetic rats.

Diabetes mellitus is known to be associated with enhanced intestinal absorption of lipids. A validated in vitro technique was used to examine the uptake of (3H) retinol (a lipid soluble vitamin) into the jejunum and ileum of streptozotocin (STZ)-induced diabetic rats. In addition, availability of vitamin A in the plasma and liver of diabetics which were pair-fed to non-diabetic control rats was investigated. The relationship between the duration of incubation and retinol uptake was curvilinear in both the jejunum and the ileum, but no difference in intestinal uptake was observed between the two groups of animals. A linear relationship was noted between the concentration of retinol and uptake into both the jejunum and ileum. There was no difference in the uptake of retinol between the diabetic and control animals. The hepatic concentration of vitamin A also remained unaffected by diabetes as indicated by similar values found between pair-fed diabetic and non-diabetic control rats. Unlike the liver, plasma retinol level was decreased in the diabetic animals; this effect does not appear to be caused by any change in the intestinal absorption of the vitamin.