Localization of gonadotrophin-releasing hormone I, bradykinin and their receptors in the ovaries of non-mammalian vertebrates.

GnRH I and its receptors have been demonstrated in the ovaries of various vertebrates, but their physiological significance in reproductive cascade is fragmentary. Bradykinin is a potent GnRH stimulator in the hypothalamus. In the present study, the presence of GnRH I and its receptor, and bradykinin and its receptor in the ovaries of non-mammalian vertebrates were investigated to understand their physiological significance. GnRH I immunoreactivity in the ovaries of fish, frog, reptile and bird were mainly found in the oocyte of early growing follicles and granulosa cells and theca cells of previtellogenic follicles. Vitellogenic follicles showed mild GnRH immunoreactivity. GnRH I-receptor and bradykinin were localized in the same cell types of the ovaries of these vertebrates. The presence of GnRH I, GnRH I-receptor and bradykinin in the ovaries of these vertebrates was confirmed by immunoblotting. The presence of GnRH I mRNA was demonstrated in the ovary of vertebrates using RT-PCR. The ovaries of reptiles and birds showed significantly higher intensity of immunoreactivity for GnRH I-receptor as compared with the fish and amphibian. This may have a correlation with the higher yolk content in the ovary of reptile and bird. These results suggest the possibility of GnRH I and bradykinin as important regulators of follicular development and vitellogenesis in the vertebrate ovary.