Factsheet 17: Gonadotroph; Aigul Ichshanova, Dinela Rushani

Factsheet 17: Gonadotroph; Aigul Ichshanova, Dinela Rushani

Proudman JA, Vandesande F, Berghman LR.Immunohistochemical Evidence That Follicle-Stimulating Hormone and Luteinizing Hormone Reside in Separate Cells in the Chicken Pituitary, Biology of Reproduction, 1999, 60, 1324-1328

Objective: The purpose of the study was to determine the localization of FSH and LH in chicken anterior pituitary gland. They did not have a stated hypothesis because the cellular distribution of FSH in avian species was unknown.

Assumptions: Cells that contained the α subunit, but were not FSH-ir (immunoreactive), were assumed to be LH gonadotrophs or thyrotrophs. There were no immunostained cells in the cephalic lobe of the pituitary where thyrotrophs are exclusively located. Therefore, it was reasonably assumed that mAbs did not cross-react with TSH.

Methods: The three independently derived mAbs (5B8G11, 16E4B6, and 20 A6B5) and rabbit pAb against LH were tested for specificity using spots with purified FSH and purified LH on the nitrocellulose disk, respectively. Two techniques were used to locate the gonadotrophs: chromogenic and dual-label immunostaining of sagittal sections of chicken pituitaries. Localization of gonadotrophs was determined in chicken of different ages (4 weeks old and >70 weeks old)and different reproductive stages (juvenile broilers versus egg-laying hens). The sample size in each case was 3.

Results: Immunostaining of sagittal sections of chicken anterior pituitary showed that FSH-ir gonadotrophs are less numerous than LH-ir gonadotrophs. They are largely absent from the outer margin of the pituitary whileLH-ir gonadotrophs are distributed throughout the anterior pituitary. Finding the localization of gonadotrophs fulfilled the stated purpose of the paper. Dual-label immunohistochemistry showed for the first time that chicken LH and FSH reside in separate population of gonadotrophs in the anterior pituitary gland. However, cells that contained both hormones were also observed, but this occurred infrequently.

Discussion: The interpretations of the results logically arose from the data and did not merely repeat them. The IHC results clearly demonstrate that the majority of gonadotrophs contain either FSH or LH. This suggests that the production and secretion of these hormones may be regulated differently in chickens than in most other species, in which most of the gonadotrophs contain both hormones. The authors recommend the chicken as an excellent model for studying the differential regulation of gonadotropin secretion. They also discussed the possibility that the blood supply to the outer cortex of the gland may differ from that of the cells in the interior of the gland which might lead to preferential depletion of FSH in one area.

The abstract briefly and accurately summarized the article, including the key methods and results.

Overall opinion: We found the paper to be well-organized. The proven specificity of the antibodies they used is of critical importance to the validity of the conclusion. We liked the fact that they used two different ways (chromogenic and immunofluorescent staining) that yielded the same results. They also tested other factors, such as age and reproductive stage. The sample size was acceptable considering the low variability in the results. We think several parallel sagittal sections should have been used to better understand localizations of gonadotrophs. In addition, they concluded that the production of hormones in separate cells is not a function of age, reproductive state and strain. However, they did not test for different strains of chickens. In general the research was welldesigned, and they provided novel evidence about the cellular organizationof avian pituitary gland.