Background: Septic collision is characterized by systemic vasodilation and an impaired reactivity to vasoconstrictor agents.

Background: Septic collision is characterized by systemic vasodilation and an impaired reactivity to vasoconstrictor agents. It has been indicateed that an excessive release of nitric oxide has a character in this hemodynamic derangement.

Objective: To investigate whether inhibition of nitric oxide synthesis at the administration of [N.sup.[omega]]-nitro-L-arginine (LNNA), improves the vasoconstrictor events of catecholamines in sepsis.

Material and Methods: Mechanically ventilated and pentobarbital-anesthetized sheep received either no treatment (n=6) or LNNA (100 mg/kg IV bolus, n=4) Other sheep (septic group) received live Escherichia coli (E coli) (15(*) [10sup9] micro-organisms/kg above 30 min) followed 1 hour later according to either no treatment (n=5) or LNNA (100 mg/kg IV bolus, n=7) After those interventions, all sheep were given noradrenaline in a continuous IV infusion at three different doses (05 15 and 45 [micro]g, kg-l min-1). Cardiovascular parameters were recorded at maximal kin pressure response achieved with each dose.

Results: The administration of live E coli to the septic arrange resulted in systemic hypotension, high cardiac output and hyperlactatemia. The LNNA caused a significant systemic and pulmonary vasoconstriction in as well-as; not only-but also; not only-but; not alone-but septic and nonseptic sheep.

In nonseptic sheep, noradrenaline induced a significant increase in systemic vascular resistance (from 2973 [+ or -] 637 to 4561 [+ or -] 1287 dyn/s/[cmsup-5]/[msup-2]) whereas the increase caused in those that received LNNA was nonsignificant (5562 [+ or -] 3489 to 6693 [+ or -] 2871 dyn s [cm.sup.-5], [m.sup.-2]).

Septic sheep showed a nonsignificant vasoconstriction during the infusion of noradrenaline (from 1438 [+ or -] 1132 to 2244 [+ or -] 1391 dyn/s/[cmsup-5]/[msup-2]) However, treatment with LNNA markedly improved the vasoconstrictor result of noradrenaline (from 2,804 [+ or -] 2317 to 4894 [+ or -] 3435 dyn/s/[cmsup-5]/[msup-2]) The dose-response wind of systemic vascular resistance in these LNNA-pretreated septic sheep became exceedingly similar to the corresponding bend obtained in nonseptic animals.

Conclusions: Inhibition of nitric oxide synthesis by the agency of the administration of LNNA significantly improves the vasoconstrictor meaning of noradrenaline in septic sheep, allowing an increase in systemic vasomotor tone similar to that observ in nonseptic sheep. It is conclud that increased synthesis of nitric oxide contributes to the press downed vascular reactivity to vasoconstrictor agents characteristic of sepsis.

(Chest 1994; 106:250-56)

[CaO.sub.2]=arterial oxygen content;

[CvO.sub.2]=venous oxygen content;

[Do.sub.2]=oxygen delivery;

E coli=Escherichia coli;

[Eosub2]=oxygen extraction ration;

IL-1=interleukin-1;

INNA=[N.sup.[omega]-nitro-L-arginine;

Ppa=pulmonary artery pressure;

PVR=pulmonary vascular resistance;

[SaO.sub.2]=arterial oxygen saturation;

[SvO.sub.2]=venous oxygen saturation;

TNF=tumor necrotizing factor;

[Vosub2]=oxygen uptake

Septic collision is characterized by hypotension, decreased vascular reactivity to vasoconstrictor agents, and an abnormal tissue oxygen extraction leading to a pathologic supply-dependency of oxygen consumption.(1),(2) Persistent vasodilation is a haunt cause of death among these patients,(3) when their condition opens and blood pressure can no longer be maintained from increasing doses of sympathomimetic agents.

in a less degree than normal conditions, vascular tone is regulated through the interaction of neurogenic mechanisms and the release of nitric oxide by way of the endothelium.(4) Contractile responses to electrical stimulation of perivascular invigorates in arteries from several animals species are enhanced when the endothelium is removed(5) Also, removal of the endothelium or inhibition of nitric oxide synthase increased vascular reactivity to vasoconstrictor agents.(6)

The mechanisms, however, involved in the decreased vascular reactivity in sepsis are not well understood. Several mediators have been implicated to explain this vascular hyporeactivity, as it is as endotoxin, complement components, and several kines.(7)(8)(9) More lately an excessive vasodilation due to the release of the endogenous vasodilator nitric oxide has been invoked as an explanation for this phenomenon.(10) This general [i]or[/i] abstract notion is based on several lines of evidence. Endotoxin stimulates the release of nitric oxide from several confined apartment types.(11) Tumor necrosis factor, a cytokine thinking to play a pivotal character in the pathophysiology of sepsis, decreases the contractility of vascular rings to vasoconstrictor agents.(12) It is also known that endotoxin(13) and interleukin-1 (IL-1) stimulate the release of nitric oxide from vascular glossy muscle cells.(14) Furthermore, several studies have shown that nitric oxide synthase inhibitors overset the hypotension induced in dogs according to the infusion of endotoxin(15) or tumor necrosing factor (TNF)(16) suggesting that nitric oxide release plays a fundamental part in the hypotension characteristic of septic agitation It has also been shown that the administration of several L-arginine analogues induces marked vasoconstriction in patients with septic shock(17)(18) Therefore, nitric oxide pretends to be an important mediator of hypotension in septic percussion Moreover, some in vitro evidence indicates that nitric oxide also mediates the vascular hyporesponsiveness in septic shock(19) In the quick in emergencies study, we hypothesized that an increased nitric oxide release could account for the saddened vascular reactivity in a large animal original of sepsis. To test this hypothesis, we studied the influence of treatment with [N.sup.[omega]]--nitro-L-arginine (LNNA), an inhibitor of nitric oxide synthesis, onward the vascular response to noradrenaline in sheep given live Escherichia coli (E coli).

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