Effect of gonadotropin (FSH + LH) and thyrotropin (TSH) administered with or without endotoxin at the age of three weeks on the response capacity of the thyroid gland in adult rats

At the age of three weeks the experimental animals received either thyrotropin (TSH), or gonadotropin (FSH + LH), or endotoxin (LPS) alone or in combination. The effectivity of the treatments was evaluated at the age of two months (with or without further hormone treatment). Contrastingly to neonatal TSH treatment, TSH treatment at the age of three weeks did not give rise to imprinting. In female animals, however, TSH treatment increased the sensitivity to the related gonadotropin hormone. At the age of three weeks gonadotropin treatment--on its own--did not cause damages to the TSH receptors of the thyroid gland. While in previous experiments neonatal endotoxin treatment damaged considerably the thyroxin production of the adult thyroid gland, after treatments at the age of three weeks no similar effect could be observed. The treatment, however, decreased the sensitivity of the receptors to TSH. In female animals simultaneous administration of endotoxin and TSH led, even without further hormone treatment, to constant increase in T4 level (the increase could also be detected in the adult animal). Imprinting, however, did not develop. In male animals simultaneous administration of endotoxin and gonadotroph hormone decreased considerably the T4 baseline level, and further TSH or gonadotropin treatment was unable to enhance T4 production.