Restricted feed intake influences thyroid hormone production and peripheral deiodination in chickens

Thyroid hormones are of major importance in determining metabolic state both in mammals and in birds. Whether or not feed intake itself has an autoregulatory role in adjusting the setpoint of thyroid hormone activity is yet not well understood. The present work investigates the effects of restricted feed intake on the serum levels and on the peripheral metabolism of thyroid hormones. Also, the sensitivity of the pituitary-thyroid axis was looked at by means of thyrotropin releasing hormone provocation test. Several groups of Hunniahybrid chickens aged 2-6 weeks were used. Restriction was made by providing the experimental animals 70 and 85 percent of the amount of food consumed in the ad libitum fed control group. It was found that feed restriction lowers circulating concentration of triiodothyronine probably by inhibiting the activity of liver deiodinase and also decreases the sensitivity of the pituitary-thyroid axis meaning that both central and peripheral regulatory mechanisms of thyroid economy are affected by feed restriction.     

Ligand-induced changes in Oestrogen and thyroid hormone receptor expression in the developing rat cerebellum: A comparative quantitative PCR and Western blot study

Oestrogen (E2) and thyroid hormones (THs) are key regulators of cerebellar development. Recent reports implicate a complex mechanism through which E2 and THs influence the expression levels of each other's receptors (ERs and TRs) to precisely mediate developmental signals and modulate signal strength. We examined the modulating effects of E2 and THs on the expression levels of their receptor mRNAs and proteins in cultured cerebellar cells obtained from 7-day-old rat pups. Cerebellar granule cell cultures were treated with either E2, THs or a combination of these hormones, and resulting receptor expression levels were determined by quantitative PCR and Western blot techniques. The results were compared to non-treated controls and to samples obtained from 14-day-old in situ cerebella. Additionally, we determined the glial effects on the regulation of ER-TR expression levels. The results show that (i) ER and TR expression depends on the combined presence of E2 and THs; (ii) glial cells mediate the hormonal regulation of neuronal ER-TR expression and (iii) loss of tissue integrity results in characteristic changes in ER-TR expression levels. These observations suggest that both E2 and THs, in adequate amounts, are required for the precise orchestration of cerebellar development and that alterations in the ratio of E2/THs may influence signalling mechanisms involved in neurodevelopment. Comparison of data from in vitro and in situ samples revealed a shift in receptor expression levels after loss of tissue integrity, suggesting that such adjusting/regenerative mechanisms may function after cerebellar tissue injury as well.