Differential Metabolism of Pregnenolone by Testicular Homogenates of Humans and Two Species of Macaques

J. J. A. M. Weusten; M. P. M. E. van der Wouw; A. G. H. Smals; J. A. Hofman; P. W. C. Kloppenborg; Th. J. Benraad

doi:10.1055/s-2007-1004987

Hormone and Metabolic Research, Table of Contents

Horm Metab Res 1990; 22(12): 619-621
DOI: 10.1055/s-2007-1004987

Originals Basic

Differential Metabolism of Pregnenolone by Testicular Homogenates of Humans and Two Species of Macaques

Lack of Synthesis of the Human Sex Pheromone Precursor 5,16-Androstadien-3β-ol in Nonhuman PrimatesJ. J. A. M. Weusten, M. P. M. E. van der Wouw¹ , A. G. H. Smals, J. A. Hofman, P. W. C. Kloppenborg, Th. J. Benraad¹

Department of Medicine, Division of Endocrinology, St. Radboud Hospital, University of Nijmegen, Nijmegen, The Netherlands
¹Department of Experimental and Chemical Endocrinology, St. Radboud Hospital, University of Nijmegen, Nijmegen, The Netherlands

Abstract

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Summary

In previous reports we described the early time sequence in in vitro [4-¹⁴C] pregnenolone metabolism in human and rat testicular homogenates and, apart from a difference in the preferred route of the conversion of pregnenolone to testosterone, we demonstrated the presence of Δ16-synthetase activity in human but not in rat testes.

In the study of testicular function higher monkeys are increasingly used as a model for human reproduction. The availability of testes from 2 different species of macaques (rhesus and crab eating monkeys) enabled us to compare the in vitro metabolism of pregnenolone in these testes with human testes. The pattern obtained in both monkey species were very similar, but completely different from those found in man. The Δ4 pathway was the preferred route for the conversion of pregnenolone to testosterone in the monkeys tested, the Δ5 pathway in the humans. Δ16-Synthetase activity, a prerequisite for the synthesis of the sex pheromone precursors 5,16-androstadien-3β-ol and 4,16-androstadien-3-one, was clearly measurable in the human but not in the monkey testicular homogenates. So far, man and boar are the only species harbouring Δ16-synthetase activity in their testes. These in vitro data indicate that the nonhuman primates studied are not suitable models for the study of human testicular function.

Key words

Testicular Homogenates - Human - Monkey - Pregnenolone Metabolism - Δ16-Androstenes

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