Immunohistochemical evidence that follicle-stimulating hormone and luteinizing hormone reside in separate cells in the chicken pituitary

As is the case in other tetrapod species, the chicken gonadotropins LH and FSH consist of a common or subunit and a hormone-specific beta subunit. Gon adotrophs containing LH were shown earlier to be distributed throughout bot h the caudal and cephalic lobes of the chicken anterior pituitary, but the cellular distribution of FSH in avian species is still uncertain. The purpo se of this study was to determine the cellular distribution of FSH-containi ng chicken gonadotrophs by use of FSH-specific monoclonal antibodies (mAbs) . Three new mAbs toward chicken FSH were proven hormone specific by immunod etection of purified hormones on dot blots and by dual-label immunohistoche mistry (IHC) on sagittal sections of chicken pituitaries. A rabbit antibody was used to detect chicken LH. Results showed that LH-containing gonadotrophs were densely distributed thr oughout the anterior pituitary, whereas gonadotrophs containing FSH were mu ch less numerous; in addition, while also present in both lobes, FSH-positi ve cells were largely absent from the outer margin of the gland. Dual-label IHC revealed that LH and FSH reside almost exclusively in separate gonadot rophs. The identity of FSH-containing cells was further confirmed through u se of an antibody to the chicken or subunit, which showed that FSH immunore activity was always colocalized with the a subunit. Our results suggest the possibility that production and secretion of LH and FSH may be regulated differently in chickens than in most other species st udied to date.