sodium-nitrite and zaprinast

The free radical peroxynitrite (ONOO-) is formed in biological systems from the reaction of nitric oxide (NO) with superoxide (O2-) and can react with protein and nonprotein thiol groups to produce tissue injury. However, these pathologic actions of (ONOO-) may have been overemphasized, in that (ONOO-) has vasorelaxant properties through activation of soluble guanylate cyclase; inhibits leukocyte-endothelial cell interactions; and reduces ischemia-reperfusion injury in the heart, lung, and liver. It has been reported that tolerance develops to the vasodilator actions of (ONOO-) and that (ONOO-) impairs vascular function. However, little, if anything, is known about responses to (ONOO-) in the hindlimb circulation of the cat. To better understand the effects of (ONOO-) on responses to vasoactive agonists and the mechanism by which (ONOO-) induces vasodilation, the effects of short-term exposure to (ONOO-) were investigated under constant-flow conditions in the hindlimb vascular bed of the cat. In these studies, direct intraarterial injections of (ONOO-) produced dose-dependent decreases in hindquarters perfusion pressure. The vasodilator responses to (ONOO-) were rapid in onset, were short in duration, and could be repeated without exhibiting tachyphylaxis. Vasodilator responses to (ONOO-) were not changed in the presence of inhibitors of nitric-oxide synthase, cyclooxygenase, or K+-ATP (adenosine triphosphate-sensitive potassium) channels. Furthermore, responses to (ONOO-) were enhanced in duration by the type 5-cGMP (cyclic guanosine monophosphate) phosphodiesterase inhibitor zaprinast, whereas rolipram, a type 4-cGMP phosphodiesterase inhibitor, was without effect. Repeated administration of (ONOO-) had no significant effect on responses to vasoconstrictor or to vasodilator agents including acetylcholine. These results show that (ONOO-) has significant vasodilator activity in the hindlimb vascular bed of the cat and suggest that the response is mediated by a cGMP- dependent mechanism. The results of experiments with repeated injections of (ONOO-) indicate that (ONOO-) does not impair vasoconstrictor and endothelium-dependent or endothelium-independent vasodilator responses. Furthermore, tolerance did not develop with repeated short-term exposure to (ONOO-). Moreover, the results of experiments with inhibitors suggest that responses to (ONOO-) are not dependent on K-ATP (adenosine triphosphate-sensitive potassium) channel activation, increased NOS activi

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; Adamantane; Animals; Cats; Female; Hindlimb; Male; Meclofenamic Acid; Morpholines; NG-Nitroarginine Methyl Ester; Nitrates; Nitric Oxide Donors; Perfusion; Peroxynitrous Acid; Phosphodiesterase Inhibitors; Potassium Channel Blockers; Purinones; Regional Blood Flow; Rolipram; Sodium Nitrite; Splanchnic Circulation; Vascular Resistance; Vasoconstrictor Agents; Vasodilator Agents

Guanylate cyclase activity in human erythrocytes is investigated by evaluating the intracellular guanosine 3',5'-cyclic monophosphate (cGMP) content in the presence of various agents that exert specific effects on soluble or particulate guanylate cyclase. The increase in the intraerythrocyte cGMP content by the soluble guanylate cyclase activators nitroprusside and NaNO2 suggests the presence of this enzyme in human erythrocytes. The effects of four different atrial natriuretic peptide (ANP) fragments on the intraerythrocyte cGMP content is also studied. ANP II and ANP III increase the intraerythrocyte cGMP content, whereas ANP I and des-Ser5,des-Ser6-ANP III are ineffective. Thus our data show that human erythrocytes possess particulate guanylate cyclase together with the soluble enzyme. The ANP fragments ANP II and ANP III also activate the erythrocyte Na+/H+ exchange. Nitroprusside, M & B 22948 (an inhibitor of cGMP phosphodiesterase), and the cGMP analogues dibutyryl cGMP and 8-bromoguanosine 3',5'-cyclic monophosphate also increase the erythrocyte Na+/H+ exchange rate. The latter data also suggest that the erythrocyte Na+/H+ exchange is regulated by cGMP.

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; 8-Bromo Cyclic Adenosine Monophosphate; Adenosine Triphosphate; Atrial Natriuretic Factor; Calcimycin; Cyclic GMP; Enzyme Activation; Erythrocytes; Guanylate Cyclase; Hemoglobins; Homeostasis; Humans; Kinetics; Manganese; Methemoglobin; Nitroprusside; Peptide Fragments; Phosphodiesterase Inhibitors; Purinones; Sodium Nitrite; Sodium-Hydrogen Exchangers

Antianaphylactic properties have been attributed to cyclic nucleotide phosphodiesterase inhibitors through increase of cyclic AMP levels, according to the concept that increases in cyclic AMP reduce release and increases in cyclic GMP enhance release. However, Coulson et al. [3] showed that the inhibition of histamine release from human lung is correlated to the inhibition of cyclic GMP hydrolysis. We studied the effect of specific inhibitors of cyclic AMP and cyclic GMP hydrolysis on the antigen-induced mediator release from rat mass cells and human basophils and on airways relaxation [4]. The results suggested that the modulation of mediator release was different from one cell type to the other, enhancement of cyclic AMP levels leading to the inhibition of release from basophils, while cyclic GMP appears to be predominantly involved in mast cells. The present paper shows that high concentrations of sodium nitrite, a stimulating agent of guanylate cyclase, inhibit histamine release from rat mast cells in the presence or absence of M&B 22948, a selective cyclic GMP phosphodiesterase inhibitor.

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; Animals; Antigens; Aza Compounds; Histamine Release; Hypersensitivity; In Vitro Techniques; Male; Mast Cells; Nitrites; Purinones; Rats; Rats, Inbred Strains; Sodium Nitrite