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

Abstract

1. 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 ovulatpry cycle; and gonadal steroidogenesis. 2. 2. Here the authors report the early and late effects of pinealectomy (Px) and sham-pinealectomy (SPx) on the estrous cycle periodicity, plasma LH, FSH and urinary 6-sulphatoxymelatonin (6-SMT) excretion in female rats. 3. 3. Female Wistar rats (3–4 months of age) were maintained on 12/12 L/D cycle. Orbital venous plexus blood and urine samples were collected from the same rat during the estrus phase before surgery, 4–7 and 55–60 days post surgery. 4. 4. Daily vaginal smears were taken to monitor the estrous cycle and they showed a time dependent increase in the estrus stage duration in Px rats (estrus stage: 1 day in control; 3–4 days after 45 days Px). 5. 5. The decrease of gonadotropins at early post Px was due to surgical stress. 6. 6. 6-SMT levels were significantly lower at 4–7 days post SPx, but at 55–60d post surgery these levels returned to control values, which indicate pineal gland integrity. The reduction in urinary 6-SMT may be attributed to a possible high level of plasma corticosterone occurring after surgical manipulations. 7. 7. 6-SMT levels in Px 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 gland.