Using the vitamin A depletion-replacement rat model to obtain testicular synchrony, we examined the reproducibility and degree of synchronization obtained by two different protocols. In the original protocol (A), synchrony was achieved by use of retinol alone. In protocol B, retinoic acid was used during the final days of vitamin A depletion as a supplement to retinol. With protocol A, a total of 56 rats were analyzed by an adaptation of a previously published method for quantifying synchrony. Animals treated by protocol A demonstrated a reproducible degree of synchrony although variability was high among individual animals. A smaller group of animals treated with protocol B demonstrated a lower degree of synchrony. In contrast, the midpoint of synchrony (point in the cycle at which 50% of the stages are more advanced and 50% are less advanced) was a more constant value and was not different between the two treatments. The midpoints of synchrony obtained from both protocols were used to calculate a cycle duration of 300 h for our strain of Sprague-Dawley rats. Our results indicate that while the use of either protocol can reproducibly provide testicular synchrony, protocol A results in a higher degree of synchrony. The ability to synchronize testes to selected stages provides sufficient experimental material for the study of the molecular and cellular events of spermatogenesis.
