Shock/Sepsis/Trauma/Critical care
Hemorrhagic Shock-Induced Vascular Hyporeactivity in the Rat: Relationship to Gene Expression of Nitric Oxide Synthase, Endothelin-1, and Select Cytokines in Corresponding Organs

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Background

Our previous work observed that vascular hyporeactivity to norepinephrine (NE) developed after hemorrhage and the response was not the same in the 4 arteries examined. To evaluate possible mechanisms involved, the present study investigated the gene expression of iNOS, eNOS, IL-1β, IL-6, TNF-α, and endothelin-1 in the corresponding organs, and the roles of nitric oxide (NO) and endothelin (ET).

Materials and methods

LAnesthetized rats (n = 7/time point/group) were hemorrhaged to a mean arterial pressure of 50 mmHg for 60 min. The vascular reactivity of the superior mesenteric (SMA), celiac (CA), left renal (LRA), and left femoral arteries (LFA) to NE was measured at baseline, at the end of the hypotensive period (E), and at 1, 2, and 4 h later in the three groups (hemorrhage, hemorrhage+NG-nitro-l-arginine methyl ester (l-NAME), an NO synthase inhibitor, or hemorrhage+PD142893, an ET receptor antagonist). Gene expression in ileum, left kidney, liver, and skeletal muscle was determined by quantitative RT-PCR at these times.

Results

Vascular reactivity of SMA, CA, LRA, and LFA to NE decreased as much as 98% over 4 h compared with baseline. This loss of responsiveness in CA and LFA was more severe than in SMA and LRA. Gene expression of iNOS, eNOS, IL-1β, IL-6, TNF-α, and endothelin-1 in the corresponding organs of select vasculatures increased markedly over baseline levels and the fold increase in mRNA levels of these enzymes and mediators in liver and skeletal muscle was higher than in ileum and left kidney. For example, at 4 h, iNOS expression was over 16-fold higher than baseline in liver and skeletal muscle, but 5- and 7-fold higher in ileum and kidney, respectively. l-NAME or PD142893 partially attenuated the decreased vascular reactivity induced by hemorrhagic shock and attenuated the changes in gene expression observed.

Conclusion

These findings suggest that the differential expression of NOS, cytokines, and endothelin-1 in different organs are associated with the development of vascular hyporeactivity after hemorrhagic shock and may account, at least in part, for the vascular bed diversity observed.

Introduction

Studies have shown that the vascular reactivity to vasoconstrictors and vasodilators can be reduced greatly after severe trauma or shock [1, 2, 3, 4, 5, 6, 7]. Many factors, including desensitized adrenoceptors [1, 8], nitric oxide (NO) [3, 7, 9, 10, 11, 12, 13], endogenous opioid peptides [4, 14], inflammatory cytokines such as TNFα [15, 16] and IL-1 [17] have been proposed to be involved in the development of vascular hyporeactivity during shock. This vascular hyporeactivity may also play an important role in the development and the outcome of the shock state, and can interfere with the therapy of shock by reducing the effectiveness of vasoactive agents [1]. It has been suggested that the low- or non-response of many patients to some vasoactive agents in the late stage of critical disease may be related to vascular hyporeactivity [1]. Consequently, it is very important to elucidate the mechanism responsible for this vascular hyporeactivity and the role of modulating factors.

Our previous work has shown that the degree of vascular hyporeactivity after hemorrhagic shock was not the same in the 4 vascular beds examined. The loss of vascular reactivity to NE in the celiac (CA) and left femoral arteries (LFA) was more severe than in the superior mesenteric artery (SMA) and left renal artery (LRA), and NO and ET-1 inhibition improved the response to NE [3]. However, the mechanism(s) involved remain to be elucidated. The present study tested the hypotheses that the vascular bed diversity in vascular hyporeactivity to NE induced by hemorrhagic shock was associated with differential gene expression of iNOS, eNOS, IL-1β, IL-6, TNF-α, and ET-1 in the corresponding organs, and that NO or ET inhibition would improve vascular reactivity by down-regulating the gene expression of these factors.

Section snippets

Animals and surgery

This study was approved by the Research Council and by the Animal Care and Use Committee of the U.S. Army Institute of Surgical Research. The experiments were performed in adherence to the National Institute of Health Guidelines on the Use of Laboratory Animals. Ninety-one male Sprague Dawley rats (Harlan, Indianapolis, IN), weighing 406 ± 44 g, were fasted 12 h but allowed water ad libitum before the experiment. On the day of experiment, rats were first anesthetized with 2 to 3% isoflurane and

Changes in vascular reactivity of SMA, LRA, CA, and LFA

Vascular reactivity to NE in the four observed arteries was decreased significantly (P < 0.01) after hemorrhagic shock (Table 2). SMA reactivity was reduced 40.9, 55.8, 69.9, and 86.1% at the end of the hypotensive period (E) and 1, 2, and 4 h later, respectively, compared with baseline. LRA reactivity was reduced 43.3, 64.9, 83.4, and 91.4%, respectively, during these times, while CA reactivity was reduced 56.8, 68.4, 88.0, and 97.0%, respectively, and LFA reactivity was reduced 69.9, 76.6,

Discussion

Although vascular hyporeactivity following various kinds of shock has been well documented [1, 2, 3, 5, 6], many of these studies only investigated overall vascular reactivity based on the changes in MAP, or the responsiveness of a single blood vessel in vitro [1, 16]. In addition, little is known about the diversity of vascular hyporeactivity in different vascular beds after shock. Our previous work found that hemorrhagic shock-induced vascular hyporeactivity to NE was not the same in the four

Acknowledgments

Presented in part at the Resuscitation in Science Symposium, American Heart Association Meeting, November 8, 2003, Orlando, FL.

This work was performed while the author (L.-M.L.) held a National Research Council Research Associateship Award at the U.S. Army Institute of Surgical Research.

We thank Dr. Phillip D. Bowman and Dr. Baiteng Zhao for their technical assistance with RT-PCR.

The opinions or assertations contained herein are the private views of the authors and are not to be construed as

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