Differential response of growing and regressing chicken ovaries to gonadotropic hormones

Abstract Steroid hormone secretion was investigated by growing left and regressing right ovaries from chick embryos under the stimulation of purified equine LH (eLH), equine FSH (eFSH), ovine LH (oLH), and ovine FSH (oFSH) in organ culture. Radioimmunoassay was used to measure the amount of steroid hormone released into the culture medium during 6 hr of incubation at 41°. Stimulation of steroid hormone production by mammalian gonadotropin was dose dependent. Studies on 17β-estradiol (E 2 ) production from the growing left ovary of the 15-day-old embryo showed that steroid biosynthesis was stimulated fourfold over the basal rate of the control ovary by mammalian LH, whereas mammalian FSH could stimulate production by only 2.5-fold. Gonadotropin stimulation of testosterone (T) production by the growing ovary of the 15-day-old embryo showed a pattern similar to E 2 production. The E 2 production of the regressing right ovary was stimulated 3.7-fold by mammalian LH and 3.2-fold by mammalian FSH. Testosterone production by the regressing ovary was stimulated sevenfold above basal level by gonadotropin. By comparing the concentrations of hormone required for the half-maximum effect (ED 50 ) for oLH, eLH, and eFSH, we found that the regressing ovary required 5 times more hormone for the same stimulating effect observed in the growing ovary. The regressing ovary required 10 times more oFSH than the growing ovary to achieve the same degree of stimulation. The results indicated that the regressing ovary has lower response to gonadotropic hormone stimulation than the growing ovary and embryonic chicken ovary receptors are more sensitive to LH-like activity than FSH-like activity. Furthermore, the right ovary, although regressing, still maintains this ability to discriminate between LH or FSH structure.