Influence of type II 5' deiodinase on TSH content in diabetic rats

The Predictive Role of Thyroid Hormone Levels for Early Diabetic Retinal Changes in Experimental Rat and Human Diabetes

Purpose

In diabetic subjects, early visual functional alterations such as color vision deficiencies (CVDs) are known to precede clinically apparent diabetic retinopathy. Prominent photoreceptor outer segment degeneration and an increase in the number of retinal dual cones (co-expressing S- and M-opsins simultaneously) have been described in diabetic rat models, suggesting a connection with the development of CVDs. As cone opsin expression is controlled by thyroid hormones, we investigated the diabetic retina in association with thyroid hormone alterations.

Methods

In rat models of type 1 and 2 diabetes, dual cones were labeled by immunohistochemistry, and their numbers were analyzed in relation to free triiodothyronine (fT3) and free thyroxine (fT4) levels. Quantification of dual cones was also performed in human postmortem retinas. Additionally, a cross-sectional case–control study was performed where thyroid hormone levels were measured and color vision was assessed with Lanthony desaturated D15 discs.

Results

A higher number of dual cones was detectable in diabetic rats, correlating with fT4 levels. Dual cones were also present in postmortem human retinas, with higher numbers in the three diabetic retinas. As expected, age was strongly associated with CVDs in human patients, and the presence of diabetes also increased the risk. However, the current study failed to detect any effect of thyroid hormones on the development of CVDs.

Conclusions

Our results point toward the involvement of thyroid homeostasis in the opsin expression changes in diabetic rats and human samples. The evaluation of the possible clinical consequences warrants further research.

Effects of hormone replacement therapy with vitamin C and E supplementation on plasma thyroid hormone levels in postmenopausal women with Type 2 diabetes

Recent studies have shown that hormone replacement therapy (HRT) can exert regulatory affects on lipid and glucose homeostasis. It has been demonstrated that hyperglycemia also involving the formation of lipid peroxides, exert several biological effects that may contribute to the onset and progression of thyroid and kidney abnormalities of postmenopausal women Type 2 diabetes. Therefore, the aim of our study was to evaluate the effect of HRT, vitamin C and E (VCE) treatments on some plasma biochemical and hematological parameters and plasma thyroid hormone levels in postmenopausal women with or without diabetes. Oral HRT and VCE supplementation were compared with no HRT treatment in 40 non-diabetic postmenopausal women and 40 postmenopausal women with Type 2 diabetes mellitus, in a 6-week randomized prospective study. In the 20 women with diabetes who received oral HRT and the 20 women with diabetes who received HRT plus VCE, there was a significant fall in urea, uric acid, creatinine, total bilirubin, conjugated bilirubin, AST, ALT, LDH values. There was no significant change in red blood cell counts, total protein, albumin, sodium, potassium, hematocrit, hemoglobin and free thyrotoxine and triiodothyronine values in postmenopausal women with diabetes or treated with oral HRT and VCE. In conclusion, daily VCE and HRT administrations seem to produce significant improvement on biochemical parameters in the blood of postmenopausal women with Type 2 diabetes. The HRT and VCE supplementations may strengthen the antioxidant defense system and they may play a role in preventing kidney and liver diseases of postmenopausal women with Type 2 diabetes.

Changes in aortic endothelial gene expressions and relaxation responses following chronic short-term insulin treatment in diabetic rats

The purpose of the present study was to examine the relationship between the changes in the expressions of several mRNAs and changes in endothelial function in streptozotocin-induced diabetic and chronic short-term insulin-treated rats. Aortas from later-stage (10 week) diabetics, but not those from their insulin-treated counterparts, showed an impaired endothelial function. We found that the mRNA expressions for 30 genes were significantly upregulated, while those for 13 other genes were downregulated in aortic endothelial cells from diabetes. In later-stage diabetes, chronic insulin treatment ameliorated the endothelial dysfunction and normalized the expressions for 20 out of the 43 genes altered in diabetes. Further, 12 of the remaining 23 genes were altered by high-dose insulin treatment in the controls. In early-stage (1 week) diabetic aortas, which did not show impaired endothelial function, expression changes were shown by only 12/30 and 5/13 of the genes up- or downregulated, respectively, in later-stage diabetes. Thus, in the diabetic aortas endothelial gene expressions and function exhibited time-related changes, and several gene expressions and endothelial function were normalized by insulin treatment. The hyperinsulinemia caused by this treatment may oppose the alterations in some gene expressions and the endothelial proliferation (cell growth-related gene expressions) that occur in established diabetes.