Release of vasopressin during suppression of oestrous cycle in rat by zoladex and hypovolemic challenge.

BACKGROUND: The vasopressin (AVP) response to hypovolemia has been compared in intact and chemically castrated rats. This functional ovariectomy was done to confirm the findings in surgical ovariectomy of how gonadal steroids modulate the release of AVP under hypo-volemic challenge. METHODS: Twenty female Sprague Dawley rats were checked for oestrous over two consecutive cycles. The ten control rats were given sub-cutaneous puncture only whereas the experimental were given Zoladex implant. On the fifteenth day all the rats were given intra-peitoneal injection of poly-ehylene glycol. All the rats were de-capitated after an hour. RESULTS: The uterine weight was significantly decreased in experimental group. The plasma AVP level was also significantly decreased in the experimental group. The pituitary AVP level was significantly increased in the experimental group. CONCLUSION: The chemical castration effected the AVP secretion, this proves that the sex steroids modulate the release of AVP secretion inspite of hypo-volemic challenge.

Effect of tamoxifen on pituitary vasopressin level.

BACKGROUND: Estrogens modulate the release of Arginine Vasopressin (AVP). There is an increased level of AVP in plasma and pituitary under osterogen hormones. METHODS: Ten rats were experimental and ten were controls. The ten experimental rats were injected tamoxifen daily subcutaneously for three days in does of 1 mg/kg body weight in 0.1 ml vegetable oil base. The ten control rats were given 0.1 ml of vegetable oil vehicle only subcutaneously. On the morning of the fourth day all the twenty rats were decapitated. Blood was centrifuged at 2500 rev/min for 15 min at 4 degrees C. Plasma was stored at -20 degrees C for assay of AVP. Pituitary gland was removed and homogenized in a test tube containing 1 ml of 0.2 molar acetic acid & stored at -20 degrees C for analysis of pituitary AVP. Uteri of all rats were removed by careful dissection & weighed. RESULTS: Uterine weight and plasma AVP levels were decreased but the pituitary AVP level was unaffected. CONCLUSION: Under Tamoxifen (anti-estrogen) effect the plasma vasopressin decreased but the level in the posterior was not affected. The effect of osterogen on Hypothalamo Pituitary axis (HPA is measurable in the hypothalamus therefore probably anti-oestrogenic effect would operate more at hypothalamic level rather than posterior pituitary. This needs further investigation at the Hypothalamus level.