Normative reproductive indices for male and female adult Sprague-Dawley rats

The Sprague-Dawley rat is traditionally used as the experimental model for the study of contraceptive agents and reproductive toxicants. Until recentl y, the normative values used to compare hormone levels after drug exposure were based on the values generated by radioimmunoassay methods developed 30 years ago. To ascertain normative reproductive indices for adult female an d male Sprague-Dawley rats over a 6-month age period, we measured luteinizi ng hormone, testosterone, anal estradiol using commercially available kits that employ updated assay techniques. In addition, sperm indices were corre lated with reproductive hormones over the same time period. Animals were ki lled at 107, 128, 156, 212, and 268 days of age irrespective (for females) of cycle stage. Serum LH levels did not change with increasing age; however , the female rats had significantly higher LH values than did the males at comparable ages (p < 0.001). Testosterone levels and sperm parameters did n ot significantly change with increasing age. Estradiol levels were signific antly higher in 107-day-old female rats than they were in female rats in al l older age groups (p < 0.01). The values reported can be used in designing and interpreting data generated in ongoing, long term toxicological and co ntraceptive studies using the rat animal model. (C) 1999 Elsevier Science I nc. All rights reserved.