Stage-synchronized seminiferous epithelium in rats after manipulation of retinol levels.

Optimal conditions for obtaining stage-synchronization of the seminiferous epithelium were investigated. In this study, 147 rats were subjected to protocols in which vitamin A deficiency was induced by feeding a diet without retinol (R-ol) or retinoic acid (RA), followed by maintenance on a diet containing RA and supplementation of R-ol by injection and diet. An acceptable degree of stage synchronization and recovery of the seminiferous epithelium was observed in 90 (61%) of the 147 rats. The effects on synchrony of variations in the protocol, including the degree of deficiency before RA maintenance, the dose and duration of RA maintenance, and the manner of injection of R-ol, were tested. Initiation of maintenance on RA when a medium degree of deficiency was achieved (4-12 g of weight loss, 3-6 days without growth) resulted in a more reliable (80% of the rats) induction of synchrony than did initiation of maintenance on RA at either a less (70% synchronized rats) or more severe (50-60% synchronized rats) deficiency. Maintenance on food containing 10 mg/kg RA gave better and more reliable synchrony (70%) than maintenance on food containing 5 mg/kg RA (less than 40%). Although the duration of this maintenance did not influence the degree of synchrony, the reliability was lower when maintenance was continued for a month or more (54%). During the interval from 33 to 128 days after resupplementation, the degree of synchronization decreased, as did the predictability of the stages, while the restoration of spermatogenesis increased. Linear regression, performed on the location of the median point of synchronization, indicated that spermatogenesis progressed at a rate of 12.4 days per cycle. The median stage of synchronization, predicted by this regression line, differed by an average of 8% of the cycle from the actual location in individual rats. Extrapolation of the regression line indicated that spermatogenesis was reinitiated in mid-to-late stage VII.