Thyroxine (T₄) promotes cell proliferation and tumor growth in prostate cancer models, but it is unknown if the increase in the triiodothyronine (T₃)/T₄ ratio could attenuate prostate tumor development. We assessed T₃ effects on thyroid response, histology, proliferation, and apoptosis in the prostate of wild-type (WT) and TRAMP (transgenic adenocarcinoma of the mouse prostate) mice. Physiological doses of T₃ were administered in the drinking water (2.5, 5 and 15 µg/100 g body weight) for 6 weeks. None of the doses modified the body weight or serum levels of testosterone, but all of them reduced serum T₄ levels by 50%, and the highest dose increased the T₃/T₄ ratio in TRAMP. In WT, the highest dose of T₃ decreased cyclin D1 levels (immunohistochemistry) but did not modify prostate weight or alter the epithelial morphology. In TRAMP, this dose reduced tumor growth by antiproliferative mechanisms independent of apoptosis, but it did not modify the intraluminal or fibromuscular invasion of tumors. In vitro, in the LNCaP prostate cancer cell line, we found that both T₃ and T₄ increased the number of viable cells (Trypan blue assay), and only T₄ response was fully blocked in the presence of an integrin-binding inhibitor peptide (RGD, arginine-glycine-aspartate). In summary, our data show that the prostate was highly sensitive to physiological T₃ doses and suggest that in vivo, an increase in the T₃/T₄ ratio could be associated with the reduced weight of prostate tumors. Longitudinal studies are required to understand the role of thyroid hormones in prostate cancer progression.

Insulin resistance develops with ageing in humans and rodents. Here, we have studied the evolution of insulin sensitivity with ageing trying to discriminate the role of adiposity from that of ageing in this process. We performed oral glucose tolerance tests and determined overall and tissue-specific glucose utilization under euglycemic-hyper-insulinemic conditions in 3-, 8-, and 24-month-old rats fed ad libitum, and in 8- and 24-month-old rats after 3 months of calorie restriction. Body composition and adipocyte-derived cytokines such as leptin, resistin, and adiponectin were analyzed. Overall insulin sensitivity decreases with ageing. Calorie restriction improves global insulin sensitivity in 8- but not in 24-month-old rats. Insulin-stimulated glucose utilization in adipose tissues decreases in 8 months, while in oxidative muscles it reaches significance only in older rats. Calorie restriction restores adipose tissue insulin sensitivity only in 8-month-old rats and no changes are observed in muscles of 24-month-old rats. Resistin and leptin increase with ageing. Food restriction lowers resistin and increases adiponectin in 8-month-old rats and decreases leptin in both ages. Visceral and total fat increase with ageing and decrease after calorie restriction. We conclude that accretion of visceral fat plays a key role in the development of insulin resistance after sexual maturity, which is reversible by calorie restriction. With aging, accumulation of retroperitoneal and total body fat leads to impaired muscle glucose uptake and to a state of insulin resistance that is difficult to reverse.