Inducible Nitric Oxide Synthase in the Rat Testis: Evidence for Potential Roles in Both Normal Function and Inflammation-Mediated Infertility1

Abstract

In vitro data have indicated that nitric oxide (NO) inhibits Leydig cell testosterone production, suggesting that NO may play a role in the suppression of steroidogenesis and spermatogenic function during inflammation. Consequently, we investigated expression of the inflammation-inducible isoform of NO synthase (iNOS) in the inflamed adult rat testis and the ability of a broad-spectrum inhibitor of NO production, L-nitro-L-arginine methyl ester, to prevent Leydig cell dysfunction during inflammation. Unexpectedly, immunohistochemical and mRNA data established that iNOS is expressed constitutively in Leydig cells and in a stage-specific manner in Sertoli, peritubular, and spermatogenic cells in the normal testis. Expression was increased in a dose-dependent manner in all these cell types during lipopolysaccharide (LPS)-induced inflammation. In noninflamed testes, treatment with the NO synthase inhibitor reduced testicular interstitial fluid formation and testosterone production without any effect on serum LH levels. Administration of the inhibitor did not prevent the suppression of testicular interstitial fluid and testosterone production that occurs within 6 h after LPS treatment. Collectively, these data indicate a novel role for iNOS in autocrine or paracrine regulation of the testicular vasculature, Leydig cell steroidogenesis, and spermatogenesis in the normal testis. The data suggest that increased NO is not the major cause of acute Leydig cell dysfunction in the LPS-treated inflammation model, although a role for NO in this process cannot be excluded, particularly at other time points. Moreover, up-regulation of iNOS may contribute to the seminiferous epithelium damage caused by LPS-induced inflammation.

Expression of Constitutive Endothelial, Neuronal and Inducible Nitric Oxide Synthase in the Testis and Epididymis of Horse

“…In addition, it has been reported that normal human spermatozoa exhibit eNOS immunostaining that correlates with sperm motility [16], and nNOS immunoreactivity has also been detected in normal rat epididymis [8]. The finding that iNOS was expressed in normal tissue as well as inflamed tissue in the rat testis suggests a unique role for NOS in the male reproductive organs [17].…”

Cytokine profiles in the testes of rats treated with lipopolysaccharide reveal localized suppression of inflammatory responses

“…More recently, we have proposed an alternative hypothesis that inflammatory responses in the testis are modified by deviation from the production of key proinflammatory cytokines, such as interleukin (IL)-1␤ and tumor necrosis factor (TNF)-␣, toward immunoregulatory, immunosuppressive, or anti-inflammatory cytokine production (27). This possibility was first suggested by observations that isolated rat testicular macrophages have a reduced capacity to produce IL-1␤ and TNF-␣ in vitro compared with macrophages from other tissues (25,32,33) and exhibit immunosuppressive characteristics in vivo (3,48).…”

“…The aim of the present study was to examine both proinflammatory and regulatory cytokine production profiles in the whole rat testis in vivo by using our well-characterized LPSinduced inflammation model (19,20,48,49). This model mimics the human response to inflammation and infection of the male reproductive tract, leading to suppression of the hypothalamic-pituitary axis, reduction in androgen production by the Leydig cells, and disruption of the developing germ cells that correlates with the severity of the inflammation (49).…”

“…This model mimics the human response to inflammation and infection of the male reproductive tract, leading to suppression of the hypothalamic-pituitary axis, reduction in androgen production by the Leydig cells, and disruption of the developing germ cells that correlates with the severity of the inflammation (49). We previously have shown that this inhibition of testis function is accompanied by a transcriptional upregulation of the inflammatory mediators IL-1␤ (21), monocyte chemoattractant protein-1 (20), and inducible nitric oxide synthase (48). However, the resident macrophages of the testis appear not to participate in the inflammatory response, and the result is a minor, transient infiltration of circulating monocytes with little or no neutrophil or lymphocyte recruitment (49).…”

Mechanisms of Inhibin Signal Transduction

“…Three additional activin-related p subunits (PC and /3E in mammals and PD in Xenopus laevis) also have been identified but do not appear to play a role in FSH regulation (Hotten er al, 1995;Oda et al, 1995;Fang et al, 1996Fang et al, ,1997Loveland ef al, 1996;Schmitt et al, 1996;O'Bryan et al, 2000;Lau et al, 2000). To date, only one a subunit has been reported.…”