Problem: In addition to having an indirect effect on the T-cell development by controlling the production of ovarian steroids, an accumulating body of evidence suggest that GnRH analogue (GnRH-A) administration may exert a thymopoietic regulatory effect that is not mediated by ovarian hormones.
Method of study: In non-ovariectomized (non-OVX) and OVX adult female AO rats treated s.c. with GnRH-A or saline (controls), over 14 days, were estimated the thymic cellularity and thymocyte expression of CD4/CD8/TCRαβ by stereological analysis and three-color flow cytometry, respectively.
Results: GnRH-A in both groups of rats diminished the thymic cellularity. In non-OVX rats GnRH-A increased the relative numbers of immature cells (CD4-8-TCRαβ−, CD4-8-TCRαβlow and CD4+8-TCRαβlow), and reduced those of positively selected CD4+8+TCRαβhigh and mature (CD4-8+TCRαβhigh, CD4+8-TCRαβhigh) cells, suggesting decelerated expression of TCRαβ followed by less efficient positive selection and further maturation of the selected cells. Differently, in OVX rats GnRH-A decreased the percentage of immature (CD4-8-TCRαβ−, CD4+8+ TCRαβ−) cells and increased those of all TCRαβhigh subsets, suggesting an increased rate of early thymocyte differentiation, more efficient positive selection and further maturation of the selected cells.
Conclusions: The effect of GnRH-A administration is affected by the presence of ovarian steroids.