A method to study preovulatory surges of gonadotropins

The aim of this study was to describe and validate a method to evaluate the preovulatory surges of gonadotropins in rats submitted to anesthesia and implantation of a jugular vein cannula in the morning of proestrus and to withdrawal of serial blood samples in the afternoon of the same day. In experiment I, to choose an adequate anesthetic, cycling female rats were anesthetized in the morning of proestrus (10:00-11:00 h) with tribromoethanol, ketamine/xylazine or tiletamine/zolazepam and a Silastic cannula was implanted into the jugular vein. Blood samples (0.6 ml) were withdrawn hourly between 12:00 and 18:00 h of the same day and, on estrus morning, the rats were decapitated and the number of ova was counted. The preovulatory gonadotropin surges as well as ovulation occurred in rats anesthetized with tribromoethanol, while they were prevented by ketamine/xylazine or tiletamine/zolazepam. To investigate if the jugular cannulation under tribromoethanol anesthesia and serial blood sampling performed in experiment I altered the magnitude of the gonadotropin surges and the number of ova, intact rats (control) or rats anesthetized with tribromoethanol followed or not by jugular vein cannulation were decapitated at 16:00 h of proestrus and in the morning of estrus. The magnitude of preovulatory gonadotropin surges and the number of ova were not different among groups. Thus, since neither tribromoethanol nor surgical procedures or serial blood sampling altered the preovulatory gonadotropin surges or the ovulation process, this method seems to be suitable for this sort of study in rats.