Cyclic AMP elevating agents synergize with inflammatory cytokines to induce an inducible type of nitric oxide synthase in cultured vascular smooth muscle cells

In vivo and ex vivo analysis of tubule function

Analysis of tubule function with in vivo and ex vivo approaches has been instrumental in revealing renal physiology. This work allows assignment of functional significance to known gene products expressed along the nephron, primary of which are proteins involved in electrolyte transport and regulation of these transporters. Not only we have learned much about the key roles played by these transport proteins and their proper regulation in normal physiology but also the combination of contemporary molecular biology and molecular genetics with in vivo and ex vivo analysis opened a new era of discovery informative about the root causes of many renal diseases. The power of in vivo and ex vivo analysis of tubule function is that it preserves the native setting and control of the tubule and proteins within tubule cells enabling them to be investigated in a "real-life" environment with a high degree of precision. In vivo and ex vivo analysis of tubule function continues to provide a powerful experimental outlet for testing, evaluating, and understanding physiology in the context of the novel information provided by sequencing of the human genome and contemporary genetic screening. These tools will continue to be a mainstay in renal laboratories as this discovery process continues and as we continue to identify new gene products functionally compromised in renal disease.

Vascular β-adrenoceptor function in hypertension and in ageing

Functional β-adrenoceptors (β-AR) have been identified and characterized in blood vessels under in vivo conditions as well as in vascular smooth muscle cells (SMC) grown in culture. Agonist occupancy of β-AR activates adenylyl cyclase (AC) via the stimulatory guanine nucleotide-binding protein (Gs) and leads to elevations in intracellular adenosine 3',5'-cyclic monophosphate levels (cAMP). Increased cAMP activates the cAMP-dependent protein kinase (PKA), with subsequent phosphorylation of various target proteins. This β-AR pathway interacts with several other intracellular signalling pathways via cross-talk, so that activation by β-AR agonists may also modulate other second messengers and protein kinases. SMC β-AR play an important role in SMC function. In intact blood vessels they mediate SMC relaxation by various intracellular mechanisms, ultimately causing a decrease in intracellular Ca2+ levels. In cultured SMC, activation of the β-AR pathway results in inhibition of cellular proliferation, the development of SMC polyploidy, and SMC apoptosis. Blood vessels from hypertensive animals are characterized by an increase in SMC cell mass, a greater incidence of SMC polyploidy in the aorta, and an impairment in the β-agonist-mediated SMC relaxation. Some of these changes may result from an attenuation of β-AR function due to agonist-induced receptor desensitization caused by the uncoupling of receptors from the Gs-AC system. The phosphorylated β-AR may in turn trigger new signals and activate different intracellular pathways. However, the details of these mechanisms are still unresolved. Since functional β-AR play such a prominent and multi-faceted role in SMC function, it is important to understand how these diverse physiological effects are mediated by this receptor system, and how they contribute to the development of hypertension. With ageing, a decrease in β-AR-Gs-AC coupling is observed, and this is implicated in the reduced responsiveness of SMC. The similarities in SMC β-AR functional changes in hypertension and in ageing suggest that the underlying mechanisms are also analogous.Key words: smooth muscle, β-adrenoceptors, cyclic AMP, protein kinase A, cell proliferation, polyploidy, relaxation, apoptosis, hypertension, ageing.

Effects of a novel guanylyl cyclase inhibitor on the vascular actions of nitric oxide and peroxynitrite in immunostimulated smooth muscle cells and in endotoxic shock

OBJECTIVE

Nitric oxide (NO), produced by the inducible isoform of NO synthase (NOS) in circulatory shock exerts cytotoxic and vasodilator effects. Part of these effects are mediated by formation of peroxynitrite, a toxic oxidant produced by the rapid reaction of NO and superoxide. Other parts of the vascular actions of NO in shock are thought to be mediated by the action of NO on the soluble guanylyl cyclase (GC) in the smooth muscle and subsequent decrease in the intracellular calcium levels. Using 1H-(1,2,4)oxadiazolo(4,3-alpha)quinoxalin-1 -one (ODQ), a potent inhibitor of GC, we studied the role of GC activation in the NO- and peroxynitrite-related vascular alterations.

DESIGN

In vitro: Controlled experiment using cultured rat aortic smooth muscle cells. In vivo: Prospective, randomized, controlled animal study.

SETTING

Experimental laboratory.

SUBJECTS

Male Wistar rats and male Swiss mice.

INTERVENTIONS

In vitro: a) Stimulation of rat aortic smooth muscle cells with bacterial lipopolysaccharide (LPS) and gamma-interferon, measurement of the production of nitrite and nitrate (breakdown products of NO), and suppression of mitochondrial respiration for 24 to 48 hrs, in the presence or absence of ODQ; and b) in norepinephrine-precontracted endothelium-denuded thoracic aortic rings, exposure to LPS (10 ng/mL) in the presence or absence of ODQ. In vivo: Rats treated in vivo with LPS (10 mg/kg iv for 3 hrs) and mice challenged with 60 mg/kg LPS ip, in the presence or absence of ODQ.

MEASUREMENTS AND MAIN RESULTS

Stimulation of rat aortic smooth muscle cells with bacterial LPS and gamma-interferon induced the production of nitrite and nitrate (breakdown products of NO) and suppression of mitochondrial respiration for 24 to 48 hrs. The amount of NO produced was slightly enhanced with ODQ (10-100 EM), whereas the suppression of mitochondrial respiration was not affected by ODQ (1-100 microM). ODQ did not affect the degree of suppression of mitochondrial respiration in response to NO donor agents or to peroxynitrite. Exposure to LPS (10 ng/mL) for 6 hrs caused a time-dependent relaxation of norepinephrine-precontracted endothelium-denuded thoracic aortic rings. This response was caused by the expression of inducible NOS and could be blocked by pharmacologic inhibitors of NOS such as N(G)-methylL-arginine. ODQ (1 microM) prevented the LPS-induced loss of vascular tone in this experimental system. Similar to the in vitro responses, there was a significant suppression of the norepinephrine-induced contractions in ex vivo experiments, in which rings were taken from animals treated in vivo with LPS (10 mg/kg for 3 hrs). ODQ treatment in vitro (1 microM) caused a complete restoration of the contractile responses. In mice challenged with 60 mg/kg LPS ip, ODQ (20 mg/kg), given either as a pretreatment or as a 4-hr posttreatment, improved survival at 24-144 hrs.

CONCLUSION

These studies indicate that GC activation does not contribute to NO- or peroxynitrite-induced cytotoxicity but does contribute to the vascular hyporeactivity induced by endotoxin in vitro and in vivo. GC inhibition alone is sufficient to influence survival in a murine model of severe sepsis.

Nitric oxide and shock

Shock can be defined as the failure of the circulatory system to provide necessary cellular nutrients, including oxygen, and to remove metabolic wastes. Although it is now recognized that more than 100 different forms of shock exist, this recognition is more a reflection of the widespread use of the term to describe a variety of disease states. For the purpose of this monograph, we concentrate on various forms of cardiovascular shock, in particular, shock that may be linked to inappropriate vasodilation from overproduction of the endogenous vasodilator, nitric oxide. Some forms of shock have been extensively studied, and convincing evidence exists for the role of nitric oxide. Other disease states have been less well characterized in terms of their association with excess nitric oxide production. Available evidence of a role for nitric oxide is discussed in the hope of stimulating the interest of investigators to explore these areas more thoroughly.