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Abstract

Variation in the end products of androgen biosynthesis and metabolism during postnatal differentiation of rat Leydig cells 
Ge,Renshan; Hardy,Matthew P.
Endocrinology 139(9): 3787-3795
Publication date: 1998


The amount of testosterone (T) secreted by Leydig cells is determined bya balance between T biosynthetic and metabolizing enzyme activities. Ithas been established that 5-androstan-3,17ß-diol (3-DIOL) isthe predominant androgen secreted by the testes of immaturerats during days 20-40 postpartum, whereas T is the majorandrogen by day 56. However, the underlying changes in T biosyntheticand metabolizing enzymes during Leydig cell development andtheir magnitudes have remained unclear. The aim of the presentstudy was to define the developmental trends for T biosyntheticand metabolizing enzymes in Leydig cells at three distinct stagesof pubertal differentiation: mesenchymal-like progenitors onday 21, immature Leydig cells on day 35, and adult Leydig cellson day 90. Production rates for precursor androgen (androstenedione),T, and 5-reduced androgens [androsterone (AO) and 3-DIOL] weremeasured in progenitor, immature, and adult Leydig cells inspent medium after 3 h in vitro. Steady state messenger RNA(mRNA) levels and enzyme activities of biosynthetic and metabolizingenzymes were measured in fractions of freshly isolated cellsat each of the three stages. Unexpectedly, progenitor cellsproduced significant amounts of androgen, with basal levelsof total androgens (androstenedione, AO, T, and 3-DIOL) 14 timeshigher than those of T alone. However, compared with immatureand adult Leydig cells, the capacity for steroidogenesis waslower in progenitor cells, with a LH-stimulated production ratefor total androgens of 84.33 ± 8.74 ng/10 cells·3h (mean ± SE) vs. 330.13 ± 44.19 in immature Leydigcells and 523.23 ± 67.29 in adult Leydig cells. The predominantandrogen produced by progenitor, immature, and adult Leydigcells differed, with AO being released by progenitor cells (72.08± 9.02% of total androgens), 3-DIOL by immature Leydig cells(73.33 ± 14.52%), and T by adult Leydig cells (74.38 ±14.73%). Further examination indicated that changes in the predominantandrogen resulted from differential gene expression of T biosyntheticand metabolizing enzymes. Low levels of type III 17ß-hydroxysteroiddehydrogenase (17ßHSD) mRNA and enzyme activity were presentin progenitor cells compared with immature and adult Leydigcells. In contrast, levels of type I 5-reductase (5R) and 3-hydroxysteroiddehydrogenase (3HSD) mRNA and enzyme activities were dramaticallylower in adult Leydig cells compared with those in progenitorand immature Leydig cells. Several T biosynthetic enzymes attainedequivalent levels in immature and adult Leydig cells, but T wasrapidly metabolized in the former to 3-DIOL by high 5R and 3HSDactivities, which were greatly reduced in the latter. Therefore,declines in 5R and 3HSD activities are hypothesized to be amajor cause of the ascendancy of T as the predominant androgenend product produced by adult Leydig cells. These results indicatethat steroidogenic enzyme gene expression is not induced simultaneously,but through sequential changes in T biosynthetic and metabolizingenzyme activities, resulting in different androgen end productsbeing secreted by Leydig cells during pubertal development.