Testes of vitamin A-deficient Wistar rats before and after vitamin A replacement, of rats irradiated in utero, and of control rats were investigated by in vivo #{176}'P magnetic resonance (MR) spectroscopy. The testicular phosphomonoester/ATP (PM/ATP) ratio ranged from 0.79 ± 0.05 for testes that contained only interstitial tissue and Sertoli cells to 1.64 ± 0.04 for testes in which spermatocytes were the most advanced cell types present. When new generations of spermatids entered the

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... us epithelium, this ratio decreased. The testicular phosphodiester/ATP (PD/ATP) ratio amounted to 0.16 ± 0.06 for testes in which Sertoli cells, spermatogonla, or spermatocytes were the most advanced cell type present. When new generations of spermatids entered the seminiferous epithelium, the PD/ATP ratio rapidly increased and finally reached a value of 0.71 ± 0.06 for fully developed testes. Taken together, specific patterns of the PM/ATP ratio, the PD/ATP ratio, and pH were obtained that were correlated to the presence of spermatogonia, spermatocytes, round spermatids, and elongated spermatids or to the absence of spermatogenic cells, Hence, a good impression of the status of the seminiferous epithelium in the rat can be obtained by in vivo 'P MR spectroscopy.