Effect of gonadotropin (FSH-LH) and thyrotropin (TSH) treatment in adolescence on TSH-sensitivity in adult rats

Hormonal imprinting is characteristic of the neonatal age, in which the receptor of the target cell matures, i.e. acquires its adult binding capacity, and cellular response becomes established in presence of the adequate hormone. The normal course of imprinting may be altered by certain molecules (related hormones, hormone analogons) which are able to bind to the receptor of the adequate hormone. The chemically related gonadotropic and thyrotropic hormones may overlap on each other's receptors not only in the perinatal age, but also in the early adulthood, and this overlap of the binding may give rise to an imprinting-like effect. An example of this phenomenon was observed in the present study, in which rats of seven weeks of age treated with gonadotropin showed a significant decrease in thyroidic response to TSH, and exposure to TSH failed to increase their basic thyroxine concentration to the normal (control) level. This depressive effect of gonadotropin was slightly reduced in the presence of LPS (endotoxin), causing membrane perturbation, while pretreatment with LPS and TSH accounted for an increased sensitivity to TSH in later phases of the rat's life. These experimental observations support the possibility of a special form of imprinting in adolescence.