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Rates of bovine photoreceptor gene transcription, as measured by nuclear run-on assays, exhibit gene-specific patterns of regulation. Here we investigate initiation and elongation in nuclear run-on assays with the use of sarkosyl to further understand the nature of these gene-specific elements. Opsin transcription, alone among several genes tested, proved sarkosyl-sensitive. This sensitivity is maximal in adult retinas, with inhibition first detected in mid-third trimester fetal retinas. Therefore, opsin transcription appears to involve different regulatory elements in adult and fetal retinas, implying a fetal to adult switch in the control of opsin gene expression. Although this regulatory switch is initially activated at a time when the fetal outer nuclear layer of the retina first achieves adult-like morphology, further maturation of opsin regulation takes place postpartum since levels of sarkosyl sensitivity are almost 5-fold greater in adult retinas compared to the 7.5 month fetus. We also show that the sarkosyl-induced reduction of opsin transcription is not due to prevention of de novo RNA polymerase II initiation in the run-on reaction, suggesting the detergent alters a positive-acting, postinitiation component of the transcriptional apparatus. Since levels of opsin transcription with sarkosyl are similar to those of the other visual transduction genes with or without sarkosyl, this detergent-sensitive transcriptional component appears to account for the singularly high, gene-specific rate of opsin transcription in retinal photoreceptor cells.

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The impact of small differences in selenium exposure during the first year of life was investigated in male Wistar rats. Forty-five rats were evaluated in two experiments. Rats were provided diets that contained sucrose as the sole carbohydrate to induce an elevation in blood triglycerides, cholesterol, glucose, and insulin. In each experiment one-half the rats received 0.1 mg Se/kg and the other half 0.2 mg Se/kg diet. Both levels of selenium supported normal activity of the marker for selenium sufficiency erythrocyte glutathione peroxidase. In experiment 1 rats were maintained in galvanized cages and in experiment 2 they were housed in stainless steel cages. In both experiments rats provided 0.2 mg Se/kg diet had fewer acellular degenerating capillaries and a higher ratio of pericyte to endothelial cells in the capillary wall than those fed 0.1 mg/kg as well as fewer vessels over the optic disc head. In the second experiment, the height of the central choroid was also greater in rats exposed to the higher level of selenium suggesting that the element protected the capillaries in this region from degeneration. In contrast to vascular tissue, the retinal parenchymal tissue was unaffected by the level of selenium exposure. These results are consistent with the hypothesis that the microvasculature has a unique requirement for selenium.

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This paper evaluates the effect of small differences in selenium exposure, within the safe range, on the glomerular vascular tufts of rats fed high-sucrose diets. In the first experiment male Wistar rats were housed in galvanized cages and were provided sucrose-based diets to induce a mild chronic insult to the microcirculation. One group of rats received the diet prepared to contain 0.10 mg Se/kg and another group 0.21 mg Se/kg. To assure that the galvanized metal cages were not influencing the results of the experiment this protocol was repeated in a second experiment wherein rats were housed in stainless steel cages. The levels of Se used supported normal activity of the long-term indicator of Se sufficiency, erythrocyte glutathione peroxidase. In both experiments rats fed diets containing 0.21 mg Se/kg had larger Bowman's capsules (P < 0.01) and vascular tufts (P < 0.01). Vascular tufts from these rats also contained a higher proportion of open capillary lumen (P < 0.01), contained less cytoplasmic and extracellular material (P < 0.001), and had larger nuclei (P < 0.001) than those fed 0.10 mg Se/kg. A third study was designed to determine if the selenium-dependent differences in nuclear size were indicative of this being a site of incorporation. Year-old rats subjected to the same protocol as those in the second experiment were given 75Se, by injection into the femoral vein, to label the sites of incorporation. Glomeruli were purified and subjected to subcellular fractionation. Ninety percent of the radioactivity was associated with the crude nuclear fraction. Purification of the crude nuclear fraction demonstrated that the radioactivity was associated with the nuclei.

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Injury to microvessels caused by the chronic consumption of sucrose can be prevented by selenium (Se). The objective of this study was to determine the temporal sequence of changes in serum triglycerides, total cholesterol, glucose, and insulin induced by sucrose and their relationship to Se status and microvascular injury. Two groups of 24 Wistar rats were fed ad libitum diets in which the entire carbohydrate was either corn starch or sucrose. Two other groups were fed identical diets supplemented with 0.1 micrograms Se/g. At 6, 8, and 10 mo, eight rats from each group were fasted for 12 h and had blood taken. Rats were then given a glucose tolerance test and killed, and their retinal microvessels were evaluated for injury. After 6 mo, sucrose-fed rats had elevated triglycerides and total cholesterol. Abnormal glucose clearance and hyperinsulemia developed after 8 mo. Evidence of microvascular injury became apparent after 10 mo. These changes did not occur in rats provided the starch-based diets, and microvascular injury did not develop in the sucrose-fed rats provided supplemental Se. Glutathione peroxidase activity was normal in all groups throughout the 10-mo experiment. These results chronicle the sucrose-induced systemic insult and show that the protective effect of Se does not occur by diminishing this insult to the microvessels.

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The purpose of the present study was to examine the effects on cataractogenesis of daily sc administration of the Ca2+ antagonist drug verapamil to diabetic rats. Streptozotocin-induced diabetic rats were given verapamil half-way through the 8-week experimental period or during the full 8 weeks of diabetes. Verapamil administration had no effect on the high blood glucose values, low circulating insulin levels, or elevated triglyceride and cholesterol concentrations in the diabetic rats. Untreated diabetic rats had a 90% incidence of cataracts. Four weeks of verapamil administration reduced this incidence to 41%, and a full 8 weeks of drug treatment further lowered the incidence to 20%. Diltiazem, another Ca2+ antagonist, lowered the incidence of cataracts in the diabetic rats to a similar extent. Verapamil administration to the diabetic animals also partially protected against the presence of retinal microangiopathy in the diabetic animals. Lenticular hydration and lipid accumulation were only indirectly related to cataractogenesis in the diabetic rats and its protection by verapamil treatment. Lenticular electrolyte imbalance, particularly Ca2+, in the diabetic animals was closely correlated with cataract formation, and verapamil significantly reduced the alterations in these ion concentrations. The present results demonstrate the efficacy of verapamil as a protective agent against cataractogenesis and some retinal damage in diabetic animals. Most importantly, this occurs in the absence of any change in the glycemic status of the diabetic animals. The findings strongly support a role for lenticular Ca2+ imbalance in cataract development in diabetes and provide initial evidence to suggest its clinical use in the diabetic population at risk for blindness.

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The effects on cardiac function of feeding a diet high in sucrose to male Wistar rats over an extended period of time (15 months) was examined. This diet produced a diabetic condition which resembled noninsulin dependent diabetes mellitus. Resting hyperglycemia, high circulating insulin and triglyceride levels were observed in these animals. Further, the sucrose fed animals were overweight in comparison to chow fed control animals. Contractile protein Ca2+-ATPase activity was measured as a biochemical estimate of cardiac contractile function. Myosin and actomyosin Ca2+-ATPase activities of isolated myofibrillar fractions from hearts of experimental animals were depressed in comparison to chow fed control rats. Myosin K+-EDTA activity was also altered. The results demonstrate for the first time a defect in contractile protein Ca2+-ATPase activity in rat hearts using a model of noninsulin dependent diabetes mellitus. As the animals were euthyroid, thyroid hormone alterations in these animals were unlikely to influence the results. The results also demonstrate that insulin could not be a direct factor associated with cardiac pathology in diabetes. Instead, cardiac dysfunction may be associated with other, as yet undefined, metabolic abnormalities which accompany the diabetic state.

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