Linear Relationship Exists Between Plasma Testosterone Level And Acute Pain Reaction Time In Male Rat

The choice of experimental animal in pain research over the years has been based on weight and in most cases taken little cognizance of the role played by sex hormones and reproductive stage of the experimental animal. This study was carried out to know the ideal quality upon which the choice of experimental animal in pain research should be based whether weight age or sex and the role played by sex/gonadal hormones in the perception of pain. Eight male prepubertal (about 4 weeks old) rats of Wistar strain were used to evaluate pain reaction time using both tail flick and hot plate model of evaluation and blood samples taken to determine the plasma testosterone concentration in all the animals before the tests. The same sets of animals were kept for the next 4 weeks under the same conditions. The experiment was repeated and pain reaction time was also evaluated in the pubertal 8 weeks old rats with blood samples collected to determine the plasma testosterone level. The results showed a significant (p<.01) increase in pain reaction time with corresponding significant (p<.01) increase in plasma testosterone level in both models of evaluation. The pubertal rats tolerated well the stimuli and subsequent increase in pain reaction time. Therefore age and sex remained important factors of consideration in the choice of animal in pain experiments.