Effect of thyroid hormones on gonadotrophin release and biosynthesis using rat pituitary cell cultures.

The effect of thyroid hormones, tri-iodothyronine (T3) and thyroxine (T4) on the gonadotrophin releasing hormone (GnRH)-induced release of LH and FSH has been studied using dispersed rat pituitary cell cultures. Both T3 and T4 significantly inhibited the release of gonadotrophins in the presence of GnRH. Actinomycin D and cycloheximide also inhibited synergistically the release of LH and FSH. The incorporation of labelled amino acids and glucosamine into LH and FSH which was stimulated by GnRH was also inhibited by T3 and T4. Gonadotrophin releasing hormone had no effect on the incorporation of labelled amino acids and glucosamine into total poteins but this incorporation was also significantly inhibited by T3 and T4, the former being the more potent.