Ultrastructural changes in granulosa cells and plasma steroid levels afteradministration of luteinizing hormone-releasing hormone in the Western painted turtle, Chrysemys picta

In this study we investigated the effects of treatment by luteinizing hormo ne-releasing hormone (LHRH) on the morphology and steroid release of ovaria n tissues in the Western painted turtle, (Chrysemys picta). In Experiment I , four adult female turtles were injected with synthetic mammalian LHRH (i. p., 500 pg/g bodyweight) and four with saline 2-3 weeks prior to ovulation. Granulosa cells from LHRH-treated turtles vs controls contained both preov ulatory follicles (16-20 mm in diameter) and small follicles (0.5-1.00 mm i n diameter) with increased RER, free ribosomes and mitochondria with swolle n cristae. An increase in the amount of cytoskeletal material (microfilamen ts) was observed in granulosa cells of the experimental turtles compared to the controls. Cytoplasmic extensions of the oocyte and granulosa cells wer e longer in the small follicles of treated animals, accounting for the obse rved increase in the thickness of the zona pellucida (ZP) over the controls . In Experiment II, administration of LHRH (i.p.) to 10 turtles during the same period triggered a substantial increase in plasma progesterone and est radiol-17 beta levels over the 10 saline-injected controls. This supports t he idea that in this species, as in mammals, steroidogenic activity in the ovarian follicles are under the control of the hypothalamic-pituitary axis. The ultrastructure and hormonal levels of the experimental animals were ty pical of untreated turtles just prior to ovulation. In this species the dev elopment of follicles and steroidogenesis can be stimulated prematurely by a releasing hormone from a nonreptilian origin. (C) 2001 Harcourt Publisher s Ltd.