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Biology of Reproduction, Vol 23, 461-479, Copyright © 1980 by Society for the Study of Reproduction

Estrogen Synthesis in Leydig Cells: Structural-Functional Correlations in Necturus Testis

GLORIA V. CALLARD 1, JACOB A. CANICK 1, , and JEFFREY PUDNEY 2

1 Department of Obstetrics and Gynecology, Laboratory of Human Reproduction and Reproductive Biology, Harvard Medical School, Boston, Massachusetts 02115
2 Department of Anatomy, University of Massachusetts Medical School, Worcester, Massachusetts 01606


The intratesticular site of estrogen biosynthesis is still somewhat controversial. Since the testis of the urodele amphibian Necturus maculosus has exceptionally high aromatase activity and is organized into a distinct glandular region that can be readily separated from another component made up mainly of seminiferous lobules, a study was undertaken to correlate function and structure of these two regions. When microsomal preparations were incubated with radiolabeled substrates, two key enzymes in estrogen biosynthesis, aromatase and 17agr-hydroxylase, were found to be concentrated in the glandular tissue. Also, spectral measurements showed that cytochrome P-450 species that bind androstenedione and progesterone, respective steroidal substrates for aromatase and 17agr-hydroxylase, were distributed between the two zones in ratios similar to their steroidogenic activities. The relative yields of radioimmunoassayable estrogen and androgen from cultured cells derived from each zone was further evidence fot the higher steroidogenic capacity of the glandular tissue.

Observations with the electron microscope indicate that active steroid synthesis in the glandular tissue could be attributed solely to numerous, highly differentiated Leydig cells, which are characterized by enormous volumes of smooth endoplasmic reticulum and mitochondria with tubular cristae. The presence of structural heterogeneities in the cell population in this region further suggests there may be functional differences among the various Leydig cell types. Although differentiating Leydig cells were seen surrounding the seminiferous lobules, they had little smooth endoplasmic reticulum. Based on structural features, it is improbable that differentiating Leydig cells, Sertoli cells, or elements other than differentiated Leydig cells in either the glandular or lobular tissues are steroidogenically active.

The functional significance of testicular estrogen is still unknown. Because of the uniquely high Leydig cell aromatase activity, the specialized anatomy of the urodele testis, and an annual cycle in which temporal changes are protracted, we conclude that Necturus is a useful animal model for further investigation of this problem.

 Submitted on April 9, 1980
Accepted on June 17, 1980




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