Measurement of rat LH with a double-antibody solid-phase radioimmunoassay: effect of LH-RH and of testosterone oenanthate in castrated animals

Abstract

A double-antibody solid-phase radioimmunoassay for the measurement of rat LH was described. The use of a solid-phase method for the second incubation resulted in a considerable saving of time as compared to the conventional double-antibody method. The sensitivity and accuracy of the method were not affected by this modification. It was found that there was a cross-reaction between the NIAMD-anti-rat-LH-serum-1 used and NIAMD-rat-FSH-RP-1. This indicates that the test system does not specifically measure rat LH but gonadotrophic activity. The RIA was tested under different experimental conditions. In male rats, the effect of castration and of subsequent treatment with testosterone oenanthate upon serum LH, and upon the weight of the seminal vesicles, the ventral prostate, and the levator ani, was examined. Serum LH rose rapidly after castration and reached 2 to 4 weeks after orchidectomy a maximum (8-9 fold increase). Subsequent treatment with testosterone oenanthate caused a rapid decrease of serum LH. The accessory sex organs showed reciprocal changes of weight. In oophorectomized rats whose pituitaries had been blocked with oestradiol monobenzoate and progesterone, a linear log-dose response of plasma LH was found after administration of various doses of synthetic LH-RH.