Necturus Testis and Reproduction 67 



ylase and aromatase activity and cytochrome P-450 content. These func- 

 tional parameters were then correlated, by means of electron micros- 

 copy, with the morphology of the Leydig cells present in the two 

 regions. In this way a direct comparison could be made concerning the 

 morphological appearance of Leydig cells, associated with different 

 stages of the spermatogenetic cycle, and their capacity for aromatization. 

 The results of the assays for 17 a-hydroxylase and aromatase in 

 microsomes prepared from the different regions of N. lewisi testes are 

 summarized in Table I. Under our assay conditions, 17 a-hydroxy- 

 progesterone is the sole product synthesized from the substrate, [ 3 H]- 

 progesterone. In all experiments both estrone and estradiol- 17 f3 are 

 products of aromatization using either [ 3 H] 19-Hydroxyandrostenedione 

 or [ 3 H] androstenedione as substrates for this enzyme. Previously we 

 localized these steroidogenic enzymes in fully developed glandular tissue 

 comprised of highly differentiated Leydig cells (Callard et al. 1980). In 

 N. lewisi, however, due to the temporal formation of the glandular 

 tissue, we have been able to show that the activity of these enzymes is 

 related to the degree of differentiation of the Leydig cells. Similar 

 results have been demonstrated in the testis of N. maculosus at the same 

 stage of the breeding cycle (Pudney et al. 1983). Thus, in both species 

 the enzymes increased in activity progressively from the least mature 

 anterior segment of the testis, containing poorly developed Leydig cells, 

 to the posterior segment possessing the glandular tissue comprised of 

 fully differentiated Leydig cells. Cytochrome P-450, which is the cata- 

 lytic component of each of the steroidogenic enzymes studied here, was 

 also measured in microsomes prepared from each of the testicular seg- 

 ments. Differences in cytochrome P-450 concentration in these regions 

 was also found to closely reflect the observed changes in activity of 

 these enzymes (Table I). 



DISCUSSION 



In his study of N. maculosus, Humphrey (1921) stated that the 

 glandular tissue developed not only by hypertrophy of the Leydig cells, 

 but also by mitotic activity of these cells. The present study on N. lewisi 

 (and also observations on N. maculosus) did not demonstrate mitotic 

 figures in the glandular tissue, at any state in its formation. These con- 

 flicting observations are difficult to reconcile, unless the mitoses of the 

 differentiating Leydig cells are so transient they can only be detected 

 during extremely short periods of the breeding season, not examined in 

 our investigations. 



It would be pertinent to discuss briefly, at this stage, the derivation 

 of the interlobular Leydig cells present in the testis of N. lewisi. This is 

 an important issue since it has long been accepted in some anamniote 

 classes, such as teleosts and urodele amphibians, that definitive Leydig 



