Effect of des-Gly¹⁰-(im-Bzl-D-his⁶)LHRH-ethylamide on hypophysial gonadotrophs and ovary of the juvenile frog Rana cyanophlyctis (Schn.)

Abstract

The effects of synthetic luteinizing hormone-releasing hormone (LHRH) (0.01 and 0.1 μg) agonist on pituitary and ovary were studied in the juvenile frog Rana cyanophlyctis with respect to their body weights. Injections (ip) were given 6 days a week for 30 days and frogs were sacrificed on the 31st day. The pituitary sections were stained with AB-PAS-OG technique. The staining intensity, cytoplasmic granulations, and length of hypophysial gonadotrophs (B₂ cells) were increased (P < 0.05) due to LHRH treatment. In controls, the B₂ cells were small and faintly stained. Treatment with LHRH (0.01 or 0.1 μ g) once a day or twice a day (0.01 μg) to frogs weighing less than 6 g body weight had no effect on gonadosomatic index (GSI) or size frequency distribution of oocytes even though gonadotrophs were hypertrophied and hyperactive. Whereas administration of LHRH (0.01 or 0.1 μg) once a day to frogs weighing around 8 g caused a significant (p < 0.05) increase in ovary weight, GSI, and diameter of the largest oocytes. Further, oocytes were recruited to second growth phase (i.e., incorporation of yolk in oocytes) due to LHRH treatment. The above findings suggest that synthetic LHRH agonist has the stimulatory effect on oocyte growth and recruitment of vitellogenic oocytes in juvenile frogs weighing around 8 g. The LHRH induces precocious maturity by incorporating yolk in oocytes. The pituitary responsiveness to LHRH agonist is also evident in juvenile frogs. The ovarian receptivity/responsiveness to endogenous gonadotrophins seems to progressively increase with the increase in the body weight of the juvenile frogs.