Résumé
In the subadult Rana tigrina administration of 2 μg luteinizing hormone releasing hormone-acetate/frog six days a week for 4 weeks in April resulted in the formation of medium (in all 8 frogs) and large sized (in 4 out of 8 frogs) yolky oocytes and, concomitant increases in the oviductal mass. The ovarian and oviductal masses showed a 10-fold increase over the control frogs. In untreated frogs the ovaries were transparent and contained first growth phase oocytes only. The oviducts were also infantile. The pituitary sections were stained using antisera raised in rabbit against the β-subunit of human luteinizing hormone and human follicle stimulating hormone. Immunoreactivity, staining intensity, cytoplasmic granulation and, cell, nuclear and cytoplasmic areas of gonadotrophs (B2 cells) increased significantly in luteinizing hormone releasing hormone treated frogs. The above findings suggest that pituitary-ovarian axis in the subadult Rana tigrina is responsive to luteinizing hormone releasing hormone and that long-term treatment with the hormone induces cytomorphological changes in the gonadotrophs which result in the conversion of inactive cells into secretory cells. This is accompanied by precocious vitellogenic growth of oocytes in the subadult frogs.