Isoforms of Nitric Oxide Synthase in the Pig Testis

Nitric oxide is a biologically active molecule involved in the regulation of main functions of the body and is produced in different cellular types by the action of molecular isoforms of the enzyme nitric oxide synthase (NOS). The presence of the isoforms defined as neuronal, testicular, endothelial and inducible has been studied in the testis of adult pigs by means of immunohistochemical techniques. Western blot analysis and a biochemical quantitative method were also performed to confirm the morphological data and to assess nitric oxide tissue activity. The NOS isoforms were contained in interstitial (Leydig), sustentacular (Sertoli), and macrophage cells, as well as in spermatogonia and spermatids. Positive Leydig cells were numerous, isolated or grouped in clusters and differed in staining intensity. Testicular extracts were found to contain four types of proteins whose molecular weight was very similar to those of the NOS isoforms. The biochemical measurement of the NO2 tissue content gave the result of 155.25 ± 21.9 nmol/mg. On the basis of a detailed bibliographic review, the findings here obtained led us to hypothesize that a) the sources of nitric oxide in the pig testis are numerous, and b) the oxide could be involved in the regulation of the following testicular functions: steroidogenesis, vasodilatation, peristalsis/permeability of seminiferous tubules and development/apoptosis of germ cells.