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Abstract

Paracrine modulation of androgen synthesis in rat Leydig cells by nitric oxide (PDF) (HTML) 
Weissman,Ben-Avi; Niu,Enmei; Ge,Renshan; Sottas,Chantal M.; Holmes,Michael; Hutson,James C.; Hardy,Matthew P.
Journal of Andrology 26(3): 369-378
Publication date: 2005

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The free radical nitric oxide (NO), generated through the oxidationof L-arginine to L-citrulline by NO synthases (NOSs), has beenshown to inhibit steroidogenic pathways. NOS isoforms are knownto be present in rat and human testes. Our study examined thesensitivity of Leydig cells to NO and determined whether NOSactivity resides in Leydig cells or in another cell type suchas the testicular macrophage. The results showed a low levelof L-[C]arginine conversion in purified rat Leydig cell homogenates.Administration of the NOS inhibitor L-N-nitro-arginine methylester (L-NAME), or the calcium chelator ethylenebis (oxyethylenenitrilo)tetraaceticacid (EGTA), had no effect on L-[C]citrulline accumulation.Increased intracellular Ca concentrations that were inducedby a calcium ionophore, or the addition of luteinizing hormone(LH), failed to affect NO formation in intact cells that werecultured in vitro. Introduction of a high concentration ofthe NO precursor L-arginine did not decrease testosterone (T)production, and NOS inhibitors did not increase T biosynthesis.However, exposing Leydig cells to low concentrations of theNO donor S-nitrosoglutathione (GSNO) induced a dramatic blockadeof T production under basal and LH-stimulated conditions. DNAarray assays showed a low level of expression of endothelialNOS (eNOS), while the neuronal and inducible isoforms of NOS(nNOS and iNOS) were below detection levels. Reverse transcriptase-polymerasechain reaction (RT-PCR) analyses confirmed these findings anddemonstrated the presence of high iNOS messenger RNA (mRNA)levels in activated testicular macrophages that produced largeamounts of NO. These data suggest that, while T productionin rat Leydig cells is highly sensitive to NO and an endogenousNO-generating system is not present in these cells, NOS activityis more likely to reside in activated testicular macrophages.

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