Two oestrous cycles. Ten days insulin treatment reduced ovarian leptin expression of rat

OBJECTIVE: Previous studies have reported a role for insulin in leptin secretion from rat ovarian cells although the time dependent effect of insulin has yet to be obtained. The study aim is to determine the time dependent effect of insulin on leptin staining intensity in the rat ovary.

METHODS: Normally cycling rats were investigated in a spontaneous cycle (control, n=6), one cycle with insulin treatment 2U/day for 5 days (D5) (n=6), and 2 cycles with insulin treatment 2 U/day for 10 days (D10) (n=6) in the Department of Histology and Embryology, Celal Bayar University, Manisa, Turkey, from May 2004 to August 2004. Histological structures and leptin staining of the ovarian cells were investigated with immuno- histochemical technique and evaluated by a semi-quantitative scoring system.

RESULTS: Number of follicles and stromal cells decreased with longer insulin treatment. No leptin staining was observed in granulosa cells of all groups. Staining intensity and H-score of the controls, D5 and D10 groups were (+++)/204, (++)/80 and (+)/9.5 for theca externa cells; (+++)/289.5, (++)/126 and (+)/65 for stroma; (++)/140, (++)/70 and (+)/21 for corpus luteum. The difference between H-scores of control and D10 groups was statistically significant in all tissue types (p<0.01).

CONCLUSION: Insulin treatment for 10 days (2 estrous cycles) reduced leptin-staining intensity in various tissues of the rat ovary and decreased follicle development in a time dependent manner.