Modulation of estrous cycle and LH, FSH and melatonin levels by pinealectomy and sham-pinealectomy in female rats

1. The pineal has been shown to have a role in controlling reproduction of polyestrus mammals (like humans and laboratory rodents). It influences the age of sexual maturation; the timing of the ovulatory cycle; and gonadal st eroidogenesis. 2. Here the authors report the early and late effects of pinealectomy (Px) and sham-pinealectomy (SPx) on the estrous cycle periodicity, plasma LH, FS H and urinary 6-sulphatoxymelatonin (6-SMT) excretion in female rats. 3. Female Wistar rats (3-4 months of age) were maintained on 12/12 L/D cycl e. Orbital venous plexus blood and urine samples were collected from the sa me rat during the estrus phase before surgery, 4-7 and 55-60 days post surg ery. 4. Daily vaginal smears were taken to monitor the estrous cycle and they sh owed a time dependent increase in the estrus stage duration in Pr rats (est rus stage: 1 day in control; 3-4 days after 45 days pr). 5. The decrease of gonadotropins at early post Pr was due to surgical stres s. 6. 6-SMT levels were significantly lower at 4-7 days post SPx, but at 55-60 d post surgery these levels returned to control values, which indicate pine al gland integrity. The reduction in urinary 6-SMT may be attributed to a p ossible high level of plasma corticosterone occurring after surgical manipu lations. 7. 6-SMT levels in Pr rats were extremely lower at 4-7 and 55-60 days post surgery, but not null, confirming the surgical removal of the pineal gland and indicating the synthesis of melatonin in sites other than the pineal gl and.