Intratesticular injection of glycerol as a model for studying the quantitative relationship between spermatogenic damage and serum FSH

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Abstract
Intratesticular injection of glycerol (1,2,3-trihydroxypropane) was evaluated as an experimental approach for studying the relationship between spermatogenic activity, i.e. relative proportion of euspermatogenic and aspermatogenic tubules in the testis, and serum concentrations of FSH. Adult rats received a single intratesticular injection of either 400 μl distilled water or five different doses of glycerol, ranging from 25 to 400 μl, and were killed after 1 or 4 weeks respectively. Injection of glycerol caused focal destruction, so that the same testes contained intact tubules, tubules with spermatogonia and Sertoli cells only, and tubules devoid of cellular material. There was a close correlation (r=−0·896) between the frequency of intact tubules and the dose of glycerol, and a similarly strong correlation (r= −0·908) between acellular tubules and the dose of glycerol. A correlation existed between FSH and euspermatogenic tubules (r= −0·758, n=122) and, conversely, between FSH and acellular tubules (r=0·820, n=122), while the correlation for tubules containing spermatogonia and Sertoli cells was only marginal (r=− 0·055). The exact relationship between FSH and spermatogenic activity in the testis was used to estimate the minimal amount of spermatogenic tissue necessary for maintaining normal serum concentrations of FSH. Only the disruption of spermatogenesis in more than 30% of seminiferous tubules in each testis caused increased serum concentrations of FSH. Serum concentrations of FSH reached the range found in castrated rats when less than 1 % of tubules were intact. These findings demonstrate (1) that a single intratesticular injection of glycerol is suitable for the study of the relationship between spermatogenic activity in the testis and FSH and (2) that a quantitative relationship exists between the extent of spermatogenic damage and serum concentrations of FSH. The observation that, in the rat, serum FSH has a diagnostic value for the extent of spermatogenic damage may be of importance for clinical evalution of testicular disorders. J. Endocr. (1987) 115, 83–90