Ultracytochemical localization of guanylate cyclase in the oviduct of estrogen-stimulated rat

CO as a cellular signaling molecule

Many biological functions of heme oxygenase (HO), such as cytoprotection against oxidative stress, vasodilation, neurotransmission in the central or peripheral nervous systems, and anti-inflammatory, anti-apoptotic, or anti-proliferative potential, have been attributed to its enzymatic byproduct carbon monoxide (CO), although roles for biliverdin/bilirubin and iron have also been proposed. In addition to these well-characterized effects, recent findings reveal that HO-derived CO may act as an oxygen sensor and circadian modulator of heme biosynthesis. In lymphocytes, CO may participate in regulatory T cell function. A number of the known signaling effects of CO depend on stimulation of soluble guanylate cyclase and/or activation of mitogen-activated protein kinases (MAPK). Furthermore, modulation of caveolin-1 status may serve as an essential component of certain aspects of CO action, such as growth control. In this review, we summarize recent findings of the beneficial or detrimental effects of endogenous CO with an emphasis on the signaling pathways and downstream targets that trigger the action of this gas.

Ultracytochemical and biochemical evidence for guanylate cyclase in guinea pig testis

Guanylate cyclase activity has been studied biochemically and cytochemically in guinea pig testis. The results of the biochemical assays indicate an equal distribution of this enzyme between the soluble and particulate fractions, which have a different sensitivity to adenosine triphosphate. The cytochemical results demonstrate that the reaction product of guanylate cyclase is detectable in the interstitial capillary endothelial cells and, in the seminiferous epithelium, mainly at the level of the adjacent surfaces of Sertoli and germ cells of the intermediate and adluminal compartments. Guanylate cyclase activity appears at the level of pachytene spermatocytes and persists throughout subsequent stages of development. The distribution in the seminiferous epithelium seems to indicate that guanylate cyclase is involved in the interrelationships between Sertoli and germ cells during gamete differentiation.