The boar testis: the most versatile steroid producing organ known

A review of the remarkable production of steroids by the testes of the boar is presented, with the principal aims of highlighting the achievements of the Leydig cells and, at the same time, pointing to the considerable deficiencies in our understanding of its biological relevance. The onset of gonadal steroidogenesis at an early stage of sex differentiation and the pattern of pre- and postnatal secretion of steroids are outlined. This is followed by a list of steroids identified in extracts of the boar testis, with emphasis on those that can reasonably be assumed to be secretory products of the Leydig cells. For example, the high concentrations of 16-unsaturated C19 and sulphoconjugated compounds are noted. Next, an impressive list of steroids found in venous blood from the boar testis is given; among them are the 16-unsaturated steroids, the oestrogens and dehydroepiandrosterone, all mainly in the form of sulphates. However, the list also includes some less likely members, such as 11-OH and 19-OH androgens as well as 5alpha-reduced steroids. Lastly, the high concentrations of steroids reported in testicular lymph, especially sulphates, are mentioned. Although roles for testosterone are uncontested, and even for the pheromone-like C19 steroids, there is little that can be said with assurance about the other compounds listed. Some speculations are made on their possible contributions to the reproductive physiology of the boar. This is done to provoke interest and, perhaps, even action towards reaching a more complete understanding of the biological significance of the steroidogenic powers of porcine Leydig cells.