Bioassay of thyrotropin in chicks with simultaneous estimation of gonadotropin

Abstract

Simultaneous determinations of thyrotropin and gonadotropin content of anterior pituitary extracts and anterior pituitary glands was made utilizing White Leghorn cockerels 12–24 hr after hatching. The uptake of 32P per milligram wet weight of thyroids or testes provided an excellent end point for estimation of hormone activity. A 5-hr treatment with hormone coupled with a 1-hr uptake of 0.3 μCi to 1.0 μCi of 32P proved to be an effective procedure. An exposure to 32P for as little as 15 min was adequate for thyroid responses, but this interval was not satisfactory for differential testes reactions. Excellent estimations of activity were obtained with milliunits of thyrotropin especially with a 3 × 3 factorial assay design. Marked differences were noted in thyrotropic and gonadotropic titers when National Institutes of Health thyrotropin (NIH-TSH) was compared with Nutritional Biochemicals Co. thyrotropin (NBC-TSH) and with Sigma Chemical Co. thyrotropin (Sigma-TSH). Pretreatment with thiourea improved the precision of the assay but responses to TSH were much lower. Assays for the thyrotropic activity of NIH-LH and NIH-FSH preparations demonstrated that appreciable TSH activity was present in the LH but not in the FSH. The relative amounts of thyrotropin present in the two gonadotropin preparations agreed closely with the estimations stated in the NIH specifications for the two hormones. Anterior pituitary glands of 28-day-old and 62-day-old cockerels contained equivalent amounts of thyrotropic activity per milligram of gland. The pituitaries of the younger birds, however, had a gonadotropin titer which was twice as great as that of the older cockerels.