Hypothalamic regulation of the pituitary-thyroid axis in the tilapia Oreochromis mossambicus

Electrolytic lesioning of the preoptic area resulted in an increase in plasma thyroxine (T4) and reverse triiodothyronine (rT3) 10 days later; plasma triiodothyronine (T3) levels were not affected, so that there was also a significant decrease in the T3:T4, but not rT3:T4, ratios. No significant changes in T4, T3, or rT3 levels were observed in fish with lesions in either the anterior or posterior portions of the lateral tuberal nucleus. The pituitary contents of growth hormone and the two prolactins were not affected by any lesion. This indicates that the preoptic area may play a role in the inhibitory regulation of the pituitary-thyroid axis in Oreochromis mossambicus, presumably by way of effects on thyrotropin secretion.