Halothane attenuates nitric oxide relaxation of rat aortas by competition for the nitric oxide receptor site on soluble guanylyl cyclase

Effects of General Anesthetics on Regulation of the Peripheral Vasculature

The heart is a passively filling pump in a circulatory system that is connected in series with distensible blood vessels. Therefore, systemic blood pressure and tissue perfusion depend upon adequate peripheral vascular tone as well as myocardial function. Likewise, pharmacologic agents that alter circulatory stability can affect one or both of these components. The generalized depressor effects of general anesthetics have been well known clinically for over 50 years. Moreover, there are many similarities in basic cellular regulatory mechanisms among the different tissue types, and general anesthetics are well known to distribute freely among the perfusion-rich tissues (eg, central nervous system, cardiovascular system, and renal system). Therefore, it is likely that the hemodynamic depression resulting from the systemic administration of anesthetics results from actions on regulatory mechanisms of the peripheral vasculature as well as on the heart. The peripheral vasculature is regulated by extrinsic neural, endothelial, and humoral mechanisms, which interact with each other as well as with intrinsic membrane and intracellular systems within the vascular smooth muscle cell. Different general anesthetics have been found to act on specific mechanisms at each of these levels. However, the large number and complexity of these known mechanisms, as well as the many anesthetic agents, has made it extremely difficult to determine which are significant in terms of the meaningful mechanisms that are responsible for anesthetic action, major side effects, or both. Current knowledge about the effects of general anesthetics on both the extrinsic intrinsic regulatory mechanisms of peripheral vascular control is reviewed.

Albumin resuscitation increases cardiomyocyte contractility and decreases nitric oxide synthase II expression in rat endotoxemia

OBJECTIVE

Hypotension and hypoperfusion during septic shock may contribute to tissue hypoxia and the intramyocardial inflammatory response that results in myocardial dysfunction. Therefore, we hypothesized that crystalloid or colloid resuscitation may alter myocardial dysfunction.

DESIGN

Randomized, controlled, prospective animal study.

SETTING

University animal laboratory.

SUBJECTS

Sprague-Dawley rats (250-300 g, n = 6/group).

INTERVENTIONS

Rats received an intraperitoneal injection of 10 mg/kg lipopolysaccharide or control. One hour later, rats were randomized to intravenous resuscitation and received either 30 mL/kg normal saline, 10 mL/kg 10% pentastarch, 10 mL/kg 5% rat albumin, or no volume.

MEASUREMENTS AND MAIN RESULTS

We measured fractional shortening of cardiomyocytes isolated 5 hrs after lipopolysaccharide or control injection. In separate identical experiments, we measured myocardial interleukin-6, macrophage inhibitory protein-2, and nitric oxide synthase II protein and messenger RNA expression. Control fractional shortening of 24.1 +/- 2.2% was decreased by lipopolysaccharide to 18.8 +/- 1.2% (p <.001). Volume resuscitation after lipopolysaccharide significantly improved fractional shortening (p <.001). In particular, albumin resuscitation increased fractional shortening to 23.5 +/- 0.9%, which was more than either saline (fractional shortening 20.1 +/- 1.7%,p <.01) or pentastarch (fractional shortening 21.4 +/- 0.9%,p <.01). Myocardial macrophage inhibitory protein-2 protein and interleukin-6 and macrophage inhibitory protein-2 messenger RNA expression and neutrophil content were elevated following lipopolysaccharide (p <.05) but were not altered by volume resuscitation. Myocardial nitric oxide synthase II protein and messenger RNA expression increased following lipopolysaccharide (p <.01) and decreased with albumin resuscitation.

CONCLUSIONS

We conclude that following lipopolysaccharide injection, volume resuscitation improves cardiomyocyte fractional shortening. Albumin resuscitation is particularly beneficial in preventing reduced cardiomyocyte contractility, and this benefit may be related to an albumin-induced reduction in nitric oxide synthase II protein and messenger RNA expression following endotoxin injection.

Anesthesia alters NO-mediated functional hyperemia

Many properties of nitric oxide, NO, (localization, diffusiveness, half-life, vasodilatory affects) have supported its potential role in mediating the link between local cerebral activity and blood flow. However, evidence that both supports and refutes a role for NO in functional hyperemia have been presented. The present study employed multiple nitric oxide synthase inhibitors, two anesthetic regimes and laser-Doppler flowmetry to test the hypothesis that NO is critically involved in mediating the functional hyperemic response within rodent whisker-barrel cortex (WBC). In urethane anesthetized animals, functional hyperemic responses were obtained both before and after 1 mg/kg atropine infusion, 30 mg/kg i.v. L-NAME (N-Nitro-L-arginine methylester) infusion, 30 mg/kg L-NA (N-Nitro-L-arginine) infusion or 25 mg/kg 7-NI (7-nitroindazole). L-NAME was also tested in a group of animals pretreated with halothane before urethane anesthesia. Neither the magnitude of the blood flow response nor its time course was altered by NO blockade or atropine administration when compared to pre-infusion controls in urethane anesthetized rats. In contrast, animals that were pretreated with halothane exhibited a 33% inhibition of functional hyperemia after L-NAME administration. Taken together, these data do not support a primary role for NO in rat WBC functional hyperemia and suggest that previous reports of inhibition may have been secondary to the anesthesia employed.

Desflurane, compared to halothane, augments phenylephrine-induced contraction in isolated rat aorta smooth muscle

PURPOSE

The mechanism responsible for the mediation of hypertension in response to increased desflurane levels is unclear. This study compared the effect of desflurane and halothane on phenylephrine (PE)-induced contraction in rat aorta ring and the effect of desflurane in the presence and absence of nitric oxide (NO) synthase activity.

METHODS

Endothelium-free rat aorta rings were exposed serially to 10(-7) M, 10(-6) M and 10(-5) M PE alone and subsequently in the presence of 2 MAC desflurane and halothane. Secondly, endothelium-free preparations were exposed to 10(-6) M PE serially in the presence of 0, 1, 2 and 3 MAC desflurane and halothane. Thirdly, using an endothelium-intact preparation, the effect of desflurane on PE-induced contraction was examined, in the presence or absence of NG-nitro-L-arginine (L-NNA), an inhibitor of constitutive and inducible NO synthase.

RESULTS

Contraction amplitudes secondary to 10(-6) and 10(-5) M PE in endothelium-free preparations were increased by 74% and 36% respectively (P <0.05) in the presence of 2 MAC desflurane compared to controls. In endothelium-free preparations, contraction amplitudes secondary to 10(-6) M PE were increased in the presence of 1 and 2 MAC desflurane by 32% and 18% respectively (P <0.05) and reduced by 16% in the presence of 3 MAC halothane (P <0.05). In endothelium-intact preparations an expected absolute increase in contraction amplitude occurred in the presence of L-NNA but the desflurane effect was detectable both in the presence and absence of L-NNA.

CONCLUSION

Our results suggest that desflurane may have a local vasoconstrictive effect independent of endothelium and NO synthase activity. The mechanism remains to be determined.

Aminoguanidine does not influence tissue extravasation of albumin in endotoxaemic rats

BACKGROUND

It is generally maintained that protein and fluid are lost from the circulation under septic conditions. The role played by an increased production of nitric oxide, by the inducible nitric oxide synthase (iNOS), in this process is unclear.

METHODS

Chloralose anaesthetised male Wistar rats received E. coli lipopolysaccharide (LPS), 3 mg kg(-1) i.v., and were studied for 5 h. Mean arterial pressure (MAP) and heart rate (HR) were monitored and haematocrit (Hct) was determined intermittently. Tissue plasma volume and tissue clearances of radiolabelled albumin over the last 2 h of the experiment were determined by a double-isotope method. In 8 rats, 2 h after LPS, aminoguanidine, an iNOS selective blocker, was given i.v. at a dose of 5 mg kg(-1). This was followed by a continuous infusion for the duration of the experiment; altogether 20 mg kg(-1) was administered. In the control group (n=8), a corresponding volume of saline was infused.

RESULTS

Aminoguanidine did not significantly influence Hct, MAP and HR, as evidenced by inter-group comparisons (Mann-Whitney test). Tissue plasma clearances of albumin and tissue plasma volume were similar in both groups.

CONCLUSION

Aminoguanidine at 20 mg kg(-1) did not reverse the haemodynamic changes induced by LPS. Neither did the drug affect the tissue plasma clearance of albumin or the tissue plasma volume.