Na+-K+-ATPase pumping activity is not directly linked to myo-inositol levels after sorbinil treatment in lenses of diabetic rats.

Changes in tissue levels of sorbitol, myo-inositol, and Na+-K+-ATPase enzyme activity have been implicated in the development of diabetic complications in animal models of the disease and in humans. The ability of the aldose reductase inhibitor sorbinil to reverse the hyperglycemia-induced changes in these lenticular metabolite and enzyme-activity levels in the streptozocin-induced diabetic rat was examined to determine what, if any, relationship exists between these changes. Two weeks of untreated diabetes did not change ouabain-inhibitable ATPase enzyme activity assayed in lens homogenates but did result in a decrease in the Na+-K+-ATPase transport activity as measured by 86Rb uptake in the intact lens. This was accompanied by a 100-fold increase in the levels of sorbitol and significant decreases in the levels of myo-inositol, ATP, and glutathione in the lens. Whereas all of these changes could be reversed by sorbinil treatment, the dose required for restoration of the depleted myo-inositol level (ED50 greater than 20 mg.kg-1.day-1) was much higher than the dose required to reverse the other changes (ED50 range 2-5 mg.kg-1.day-1). These results suggest that the restoration of lenticular Na+ -K+ -ATPase activity is not secondary to a normalization of myo-inositol levels and may provide evidence that the two parameters are not strictly associated in diabetic tissues.

Effects of the aldose reductase inhibitor sorbinil on the isolated cultured rat lens.

The isolated cultured rat lens has been used to examine the effects of the aldose reductase inhibitor sorbinil on lenticular polyol accumulation and sugar cataract formation. Lenses incubated in medium containing 35 mmol/L glucose accumulated sorbitol over a seven-day period without the appearance of overt opacities. Sorbitol accumulation was inhibited in a dose response fashion by sorbinil with an IC50 of 3.1 X 10(-6) mol/L. In lenses incubated in the presence of 29.5 mmol/L xylose, xylitol accumulation was accompanied by an increase in the water content of the lens and the development of a classical sugar cataract. All of these effects could be prevented by the addition of sorbinil to the culture medium. Complete inhibition of cataract formation required greater than an 80% inhibition of the xylitol accumulation. Reversal of a preformed xylose cataract by sorbinil could be achieved if the inhibitor was added at the stage of cortical opacities (20 h). Cataract progression proceeded normally over the next 48 hours and then the lens slowly began to clear. The rate of the reversal was dependent on the dose of sorbinil.

Synthesis an accumulation of putative neurotransmitters by cultured neural crest cells.

The events mediating the differentiation of embryonic neural crest cells into several types of neurons are incompletely understood. In order to probe one aspect of this differentiation, we have examined the capacity of cultured quail trunk neural crest cells to synthesize, from radioactive precursors, and store several putative neurotransmitter compounds. These neural crest cultures develop the capacity to synthesize and accumulate acetylcholine and the catecholamines norepinephrine and dopamine. In contrast, detectable but relatively little synthesis and accumulation of 5-hydroxytryptamine gamma-aminobutyric acid, or octopamine from the appropriate radiolabeled precursors were observed. The capacity for synthesis and accumulation of radiolabeled acetylcholine and catecholamines is very low or absent at 2 days in vitro. Between 3 and 7 days in vitro, there is a marked rise in both catecholamine and acetylcholine accumulation in the cultures. These findings suggest that, under the particular conditions used in these experiments, the development of neurotransmitter biosynthesis in trunk neural crest cells ijs restricted and resembles, at least partially, the pattern observed in vivo. The development of this capacity to synthesize and store radiolabeled acetylcholine and catecholamines from the appropriate radioactive precursors coincides closely with the development of the activities of the synthetic enzymes choline acetyltransferase and dopamine beta-hydroxylase reported by others.