Performance of closed-loop resuscitation in a pig model of haemorrhagic shock with fluid alone or in combination with norepinephrine, a pilot study

We evaluated the performance of a new device to control the administration of fluid alone or co-administration of fluid and norepinephrine in a pig model of haemorrhagic shock in two sets of experiments. In the first one, resuscitation was guided using continuous arterial pressure measurements (three groups: resuscitation with fluid by a physician, CL resuscitation with fluid, and CL resuscitation with fluid and norepinephrine). In the second one, resuscitation was guided using discontinuous arterial pressure measurements (three groups: CL resuscitation with fluid alone, CL resuscitation with fluid and moderate dose norepinephrine, and CL resuscitation with fluid and a high dose of norepinephrine). Pigs were resuscitated for 1 h. In the first set of experiments, proportion of time spent in the target area of 78-88 mmHg of systolic arterial pressure was not statistically different between the three groups: manual, 71.2% (39.1-80.1); CL with fluid, 87.8% (68.3-97.4); and CL with fluid and norepinephrine, 78.1% (59.2-83.6), p = 0.151. In the second set of experiments, performance of CL resuscitation with fluid or with combination of fluid and high or moderate dose of norepinephrine was not significantly different (p = 0.543 for time in target). Pigs resuscitated with norepinephrine required less fluid and had less haemodilution than pigs resuscitated with fluid alone. Performance of CL resuscitation using continuous arterial pressure measurement was not significantly different than optimised manual treatment by a dedicated physician. Performance of CL resuscitation was reduced with discontinuous arterial pressure measurements in comparison with continuous arterial pressure measurements.

Performance of closed-loop resuscitation of haemorrhagic shock with fluid alone or in combination with norepinephrine: an experimental study

Background

Closed-loop resuscitation can improve personalization of care, decrease workload and bring expert knowledge in isolated areas. We have developed a new device to control the administration of fluid or simultaneous co-administration of fluid and norepinephrine using arterial pressure.

Method

We evaluated the performance of our prototype in a rodent model of haemorrhagic shock. After haemorrhagic shock, rats were randomized to five experimental groups: three were resuscitated with fluid and two with co-administration of fluid and norepinephrine. Among groups resuscitated with fluid, one was resuscitated by a physician and two were resuscitated according to two different closed-loop algorithms. Among groups resuscitated with fluid and norepinephrine, one was resuscitated by a physician and the other one by the closed-loop device. The precision of arterial pressure during the resuscitation period was assessed using rising time, time passed in the target area and performance error calculations.

Results

Groups resuscitated with fluid had similar performances and passed as much time in the target area of 80–90 mmHg as the manual group [manual: 76.8% (67.9–78.2), closed-loop: 64.6% (45.7–72.9) and 80.9% (59.1–85.3)]. Rats resuscitated with fluid and norepinephrine using closed-loop passed similar time in target area than manual group [closed-loop: 74.4% (58.4–84.5) vs. manual: 60.1% (46.1–72.4)] but had shorter rising time to reach target area [160 s (106–187) vs. 434 s (254–1081)] than those resuscitated by a physician. Rats resuscitated with co-administration of fluid and norepinephrine required less fluid and had less hemodilution than rats resuscitated with fluid alone. Lactate decrease was similar between groups resuscitated with fluid alone and fluid with norepinephrine.

Conclusions

This study assessed extensively the performances of several algorithms for closed-loop resuscitation of haemorrhagic shock with fluid alone and with co-administration of fluid and norepinephrine. The performance of the closed-loop algorithms tested was similar to physician-guided treatment with considerable saving of work for the caregiver. Arterial pressure closed-loop guided algorithms can be extended to combined administration of fluid and norepinephrine.

Electronic supplementary material

The online version of this article (10.1186/s13613-018-0436-0) contains supplementary material, which is available to authorized users.

In vivo reactive oxygen species production induced by ischemia in muscle arterioles of mice: involvement of xanthine oxidase and mitochondria

Reactive oxygen species (ROS) participate in tissue injury after ischemia-reperfusion. Their implication in leukocyte adherence and increase in permeability at the venular side of the microcirculation have been reported, but very little is known about ROS production in arterioles. The objective of this work was to evaluate, in the arteriole wall in vivo, the temporal changes in superoxide anion production during ischemia and reperfusion and to identify the source of this production. Mouse cremaster muscle was exposed to 1 h of ischemia followed by 30 min of reperfusion, and superoxide anion production was assessed by a fluorescent probe, i.e., intracellular dihydroethidium oxidation. During ischemia, we found a significant increase in dihydroethidium oxidation; however, we observed no additional increase in fluorescence during the subsequent reperfusion. This phenomenon was significantly inhibited by pretreatment with superoxide dismutase. Allopurinol (xanthine oxidase inhibitor) or stigmatellin [Q(o)-site (oriented toward the intermembrane space) inhibitor of mitochondrial complex III] or simultaneous administration of these two inhibitors significantly reduced superoxide production during ischemia to 80%, 88%, and 72%, respectively, of that measured in the untreated ischemia-reperfusion group. By contrast, no significant inhibition was found when NADPH oxidase was inhibited by apocynin or when mitochondrial complex I or complex II was inhibited by rotenone or thenoyltrifluoroacetone. A significant increase in ROS was found with antimycin A [Q(i)-site (located in the inner membrane and facing the mitochondrial matrix) inhibitor of mitochondrial complex III]. We conclude that a significant increase in ROS production occurs during ischemia in the arteriolar wall. This increased production involves both a cytoplasmic source (i.e., xanthine oxidase) and the mitochondrial complex III at the Q(o) site.

Characteristic features of in vivo skin microvascular reactivity in CADASIL

CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy) is caused by mutations in the Notch3 receptor expressed at the surface of vascular smooth muscle cells. The functional consequences of the disease at the peripheral microcirculation level are incompletely elucidated. In this study, we aimed to assess, in vivo, the endothelium-dependent and independent vasodilation of the skin microvasculature in CADASIL patients. Twenty-three affected subjects were compared with 23 gender and age-matched controls. The brachial artery endothelium-dependent and endothelium-independent vasodilation were assessed after forearm cuff occlusion and nitroglycerin administration. Skin vasoreactivity to transcutaneous administration of acetylcholine and sodium nitroprussiate, and after postocclusive hyperemia were measured by Laser Doppler flowmetry. The maximum changes in the diameter of the brachial artery after the cuff release or after nitroglycerin administration did not differ between patients and controls. With iontopheresis, only the peak value of the dose response was found decreased in normocholesterolemic patients after nitroprussiate administration. The postocclusive test revealed a large increase of the time to peak value and whole duration of the hyperemic response in CADASIL patients. The results of this study show that the skin vasoreactivity is altered in CADASIL. Particularly, the kinetics of reactive hyperemia after cuff occlusion is dramatically changed with a lengthened and delayed response. This characteristic pattern may be related to the specific ultrastructural modifications related to Notch3 gene mutations involving smooth muscle cells in the microvasculature.

Effects of vasopressin, norepinephrine, and l-arginine on intestinal microcirculation in endotoxemia*

OBJECTIVE

The effects of vasopressin, norepinephrine, and L-arginine alone or combined on intestinal microcirculation were evaluated in the septic mouse by intravital microscopy, with which we measured the erythrocyte flux and velocity in villus tip arterioles and the density of perfused villi.

DESIGN

Controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Female BALB/c mice weighing between 18 and 21 g.

INTERVENTIONS

Anesthetized and ventilated mice received at t0 an intravenous injection of Escherichia coli endotoxin (2 mg/kg bolus intravenously), inducing after 1 hr (t60) a decrease in mean arterial blood pressure to 40-50 mm Hg associated with a significant decrease in erythrocyte flux and velocity in villus tip arterioles and in the density of perfused villi. The mice then received a randomly different treatment for endotoxin-induced shock. Treatments consisted in continuous intravenous infusion for 1 hr with either saline (control group), norepinephrine, vasopressin, L-arginine, vasopressin+L-arginine, or norepinephrine+L-arginine. The doses of vasopressors (used alone or combined with L-arginine) were titrated to restore mean arterial pressure to the baseline level.

MEASUREMENTS AND MAIN RESULTS

At the end of the treatment (t120), we observed in the control group further decreases in arteriolar flux and velocity and in the density of perfused villi. In the groups treated by a vasopressor alone, mean arterial pressure returned to baseline and there were no additional decreases in arteriolar flux and velocity or in the density of perfused villi. However, these latter three variables did not return to their preshock baseline values. Even though L-arginine did not restore mean arterial pressure, the infusion of L-arginine alone prevented the decrease in flux or erythrocyte velocity occurring between t60 and t120 and conserved to some extent the density of perfused villi compared with that in the control groups. In addition, we found that simultaneous administration of norepinephrine or vasopressin with L-arginine improved all microcirculation variables more efficiently than either vasopressor alone.

CONCLUSIONS

From these data, we conclude that a) restoring mean arterial pressure after 1 hr of endotoxemia was not sufficient to restore ad integrum intestinal mucosa microvascular perfusion; b) L-arginine could have a beneficial effect at the microcirculatory level, which was independent of mean arterial pressure; and c) administration of L-arginine combined with the maintenance of perfusion pressure by vasopressive drugs allowed a better preservation of intestinal microcirculation at an early stage of endotoxemia.

Microcirculation in intestinal villi: a comparison between hemorrhagic and endotoxin shock

Using intravital microscopy, we studied the effects of hemorrhagic and endotoxin (ETX) shock on the velocity of erythrocytes (red blood cells [RBC]) and the density of perfused villi in mouse small intestine. The mice were divided into four groups: control, normotensive sepsis (a low ETX group, 1.5 mg/kg intravenously), hypotensive sepsis (a high ETX group, 10 mg/kg intravenously), and a hemorrhagic group. One hour after endotoxemia or hemorrhage was induced, mean arterial pressure significantly decreased in the high ETX and hemorrhagic groups (72.5 +/- 1.0 mm Hg in the control group, 71.0 +/- 2.4 in the low ETX group, 42.7 +/- 1.8 in the high ETX group, 43.0 +/- 1.4 in the hemorrhagic group, respectively). We found significant decreases in RBC velocities in the villous tip and capillaries in both ETX groups but not in the hemorrhagic group (in villus tip arteriole, 1.25 +/- 0.02 mm/s, 0.80 +/- 0.02, 0.15 +/- 0.01, 1.20 +/- 0.08; in villus capillaries, 0.55 +/- 0.02, 0.38 +/- 0.02, 0.10 +/- 0.01, 0.61 +/- 0.02, for control, low ETX, high ETX, and hemorrhagic groups, respectively). We also found a significant decrease in the density of RBC-perfused villi in the high ETX and hemorrhagic groups but not in the low ETX or control groups. However, the change in the hemorrhagic group was much less than in the high ETX group (100.0 %, 95.2 +/- 1.6, 32.5 +/- 1.9, 87.3 +/- 3.4, for control, low ETX, high ETX, and hemorrhagic groups, respectively). We concluded that ETX induces a significant decrease in mucosal perfusion characterized by a diminution in RBC velocity and flux in villi found even in a normotensive situation. At a high dose of ETX, these changes are associated with a significant decrease in the number of perfused villi. In addition, we found that at the same level of hypotension, hemodynamics and mucosal perfusion disorders are considerably larger in ETX-induced hypotension than in hemorrhagic hypotension.

In vivo study of the effect of systemic hypoxia on leukocyte-endothelium interactions

To evaluate the effect of systemic hypoxia on leukocyte-endothelium interactions in peripheral tissues, we studied by intravital microscopy leukocyte rolling velocity and adherence in venules of rat cremaster muscle. We examined the possible roles of changes in blood oxygenation, peripheral tissue oxygenation, changes in local shear rate, and the involvement of integrins. Six groups of rats submitted to either control normoxic conditions, or systemic hypoxia (PO2 = 51 mm Hg) associated with either low O2 tension of Krebs superfusing the muscle, high O2 tension of the Krebs superfusing the muscle, anti-lymphocyte function-associated antigen (LFA)-1beta antibody, pentoxifylline, or normoxic conditions associated with partial occlusion of the artery perfusing the muscle. We found that: (1) systemic moderate hypoxia resulting from purely respiratory disturbance even in the absence of local stop-flow phenomenon or circulatory shock can induce an increase in leukocyte adhesion and a decrease in leukocyte rolling velocity in the microcirculation of peripheral tissues; (2) to be present, this increase in leukocyte adhesion does not require tissue hypoxia of the peripheral tissue but the effect of systemic hypoxia on rolling velocity is prevented by tissue oxygenation; (3) this increase in leukocyte adhesion is mediated by CD11/CD18 integrins but is not due to changes in local shear rate.

Role of multimerized porcine thyroglobulin in iodine storage

Thyroglobulin (Tg), the prothyroid hormone, is stored in the lumen of the thyroid follicles as soluble dimers and tetramers and insoluble multimers, Soluble Tg is well characterized with regards to structure and role, but insoluble Tg (i-Tg) is not. Here we show that i-Tg, multimerized through formation of disulfide and dityrosine bonds, has a higher iodine content than soluble Tg and no thyroid hormones. Furthermore, the size and the resistance of i-Tg to proteolytic enzymes implied a new mechanism by which thyrocytes may degrade this form of Tg. Using peroxidase and H2O2 generating system, we found that about 80% of i-Tg was degraded and 24% of its iodine content was released. Our data point to a role for i-Tg in iodine storage and the involvement of TPO in i-Tg degradation and iodide release.

A micromethod for quantitative determination of iodoamino acids in thyroglobulin

We describe a new method for quantification of iodoamino acids after enzymatic hydrolysis of thyroglobulin. The procedure involves separation of monoiodotyrosine (MIT), di-iodotyrosine, tri-iodothyronine and thyroxine by reverse phase HPLC with a Vydac C18 stationary phase and a mobile phase of water-acetonitrile-acetic acid. The separation is monitored by sensitive spectrophotometric detection through a 96-well microplate system based on the catalytic Sandell-Kolthoff reaction of iodide on the oxidation of arsenic(III) by cerium(IV). This new microassay is particularly convenient because of its high sensitivity and its rapidity (less than 2 h). It can detect 1 pmol MIT and 0.5 pmol of the other three iodoamino acids with a recovery higher than 96%. Moreover, the 96-well microplate system allows many samples to be tested simultaneously and avoids the use of radiolabeled iodine.

Dityrosine bridge formation and thyroid hormone synthesis are tightly linked and are both dependent on N-glycans

Formation of dityrosine bridges is a ubiquitous process mainly attributed to oxidative stress leading to protein degradation and cellular damages. Here we show that dityrosine formation is involved in a physiological process, thyroid hormone synthesis, and is strictly dependent on structural characteristics, namely N-glycans, presented by the protein acting as the prothyroid hormone. We used two isoforms of the N-terminal thyroid hormone forming domain (NTD) of human thyroglobulin: one without N-glycan (19 kDa isoform) and the other with high mannose type structures (25 kDa isoform). Both isoforms were able to form iodotyrosines after in vitro iodination. However, iodotyrosine coupling to form thyroxine did not occur with the unglycosylated 19 kDa NTD. In contrast, the 25 kDa isoform formed thyroxine. Strikingly, thyroxine synthesis was accompanied by dimerization of the 25 kDa isoform and formation of a dityrosine bridge; none of this was observed with the 19 kDa isoform. Taken as a whole, our results indicate that dimerization through dityrosine bridging accompanies and could have a role in thyroid hormone synthesis.

Differences between cytokine effects in the microcirculation of the rat

We studied by in vivo microscopy in rat cremaster muscle the acute and delayed effects of short exposure to tumor necrosis factor (TNF), interleukin (IL)-1 beta, and IL-6 on basal tone and vascular reactivity of second- to fourth-order arterioles (A2-A4). A 20-min exposure to recombinant human (rh) TNF (0.1-10 ng/ml) induced a significant arteriolar vasodilation, but no significant changes in basal tone were found after exposure to the same doses of IL-1 beta. In contrast, the same exposure to IL-6 (0.1-10 ng/ml) induced a significant dose-dependent vasoconstriction (i.e., 8, 15, and 21% at 10 ng/ml in A2-A4 arterioles, respectively). This vasoconstriction was inhibited by the thromboxane A2 receptor antagonist SQ-29548. We did not find any significant effect of rhTNF or IL-6 on vascular reactivity to norepinephrine immediately after exposure to these two cytokines or 100 min after the end of the exposure. Contrastingly, a large dose-dependent decrease in reactivity to norepinephrine was found immediately after exposure to IL-1 beta and still persisted 100 min after the end of the exposure. Such a decrease was not found for the vasoconstriction in response to KCl. We conclude that, at the microvascular level, large differences exist between the three cytokines generally considered to mediate the harmful cardiovascular effects in sepsis. 1) TNF but not IL-1 beta is responsible for a vasodilatory effect, whereas the effect of IL-6 is a thromboxane A2-mediated vasoconstriction. 2) Short exposure to IL-1 beta but not to rhTNF or IL-6 diminishes the response of the arterioles to norepinephrine but not to KCl.

Effects of tumor necrosis factor and interleukin-1 on the constriction induced by angiotensin II in rat aorta

To better understand the different steps in the changes occurring in vascular reactivity during sepsis, we studied the effects of a short exposure to tumor necrosis factor (TNF) and interleukin-1 (IL-1) on the contraction in response to angiotensin II (ANG II). The contraction elicited by ANG II was studied by using standard isometric tension techniques in aortic rings exposed for 1 h to 25 ng/ml TNF or to 5 or 20 ng/ml IL-1. This contraction was not significantly changed by TNF but was 109 +/- 23 and 190 +/- 38% greater than in control rings after 5 and 20 ng/ml IL-1, respectively. Because the contraction induced by ANG II is modulated by the simultaneous release of prostaglandins, we tested the hypothesis that IL-1 interferes with this modulation. We found that the IL-1-induced increase in contraction in response to ANG II was completely inhibited by 10(-5) M of the cyclooxygenase inhibitor indomethacin and also by 10(-5) M of the prostaglandin H2/thromboxane A2-receptor antagonist SQ-29548. Note, however, that in rings exposed to IL-1 the contraction in response to the thromboxane A2-receptor agonist U-46619 was not significantly different from the contraction in unexposed rings. Furthermore, no loss was observed in either the vasodilator response to 10(-9)-10(-4) M of the endothelium-dependent-receptor agonist acetylcholine or in the receptor-independent contraction induced by 60 mM K+. We conclude that short exposure to IL-1, but not to TNF, produces a specific increase in the vasoconstrictor response to ANG II via mechanisms mediated by prostaglandin H2/thromboxane A2. This increase might result from an IL-1-induced shift in favor of constrictor prostanoids in the balance of the dilator/constrictor prostanoids, the release of which is associated with stimulation by ANG II.

N-glycans modulate in vivo and in vitro thyroid hormone synthesis. Study at the N-terminal domain of thyroglobulin

Thyroglobulin (Tg) is the substrate for thyroid hormone biosynthesis, which requires tyrosine iodination and iodotyrosine coupling and occurs at the apical membrane of the thyrocytes. Tg glycoconjugates have been shown to play a major role in Tg routing through cellular compartments and recycling after endocytosis. Here we show that glycoconjugates also play a direct role in hormonosynthesis. The N-terminal domain (NTD; Asn1-Met171) of human Tg, which bears the preferential hormonogenic site, brings two N-glycans (Asn57 and Asn91). NTD preparations were purified from Tg with low and mild iodine content in vivo and from poorly iodinated Tg after in vitro iodination and coupling. NTD separated from poorly iodinated Tg was also submitted to iodination and coupling after desialylation and deglycosylation. The various NTD isoforms were analyzed for their N-glycan structures and hormone contents. Our results show that 1) in vivo as well as in vitro unglycosylated isoforms did not synthesize hormones, whereas fully or partially (at Asn91) glycosylated isoforms did; 2) high mannose type structures enhanced the hormone content; and 3) desialylation did not affect in vitro hormone synthesis. Evidence of a direct involvement in hormonosynthesis adds to the role of N-glycans in Tg function and opens the way to new mechanisms for regulation (e.g. TSH modulation of N-glycan) or alteration (e.g. Asn91 mutation) of thyroid hormone synthesis.

Leukocyte adherence in an ischemic muscle perfused by a collateral circulation

Leukocyte adherence was studied in an original experiment that allowed study of the microcirculation in an ischemic muscle perfused by a collateral circulation. In this model, the artery feeding the cremaster muscle was ligated. Then the muscle homolateral to the ligation and its contralateral muscle were both studied by intra-vital-microscopy at 4 h, 1, 3, 7, and 21 days after the ligation. Rats were treated or not with 20 mg/kg/day pentoxifylline (PTX) i.m. In untreated rats, we found that both short-lasting and long-lasting leukocyte adherence was largely increased in the postcapillary venules of the ischemic muscle but not in its contralateral control. This dramatic increase was not limited to the hours immediately after the arterial ligation but was also found up to 3 weeks after the ligation when blood flow was almost restored to normal. This suggested that when muscle blood flow was chronically reduced, some changes promoting leukocyte adherence may occur in the endothelium. In rats treated with PTX, we found very effective inhibition of leukocyte adherence.

Malformin-A1 inhibits the binding of interleukin-1 beta (IL1 beta) and suppresses the expression of tissue factor in human endothelial cells and monocytes

Malformin-A1, a cyclic pentapeptide of microbial origin, antagonized in a competitive manner the binding of 125I-IL1 beta (interleukin-1 beta) to human monocytes and cultured human umbilical vein endothelial cells (HUVEC) with IC50 values (doses which reduce specific binding by 50%) of 250 +/- 80 and 230 +/- 25 nM, respectively (N = 3). IL1 increased in a dose-dependent manner the expression of tissue factor, a ubiquitous membrane-anchored glycoprotein that initiates blood coagulation at the surface of HUVEC and human monocytes. Malformin-A1 strongly inhibited IL1-induced tissue factor expression in HUVEC and monocytes with IC50 values of 420 +/- 35 and 105 +/- 25 nM, respectively (N = 3), and reduced IL1-induced expression of intercellular adhesion molecule-1 (ICAM-1, CD54) on HUVEC (IC50 = 125 +/- 18 nM) (N = 4). These observations demonstrate that malformin-A1 recognizes and blocks IL1 beta binding to its receptor sites on monocytes and endothelial cells and protects these cells from IL1-induced procoagulant changes.

Nitric oxide-independent response to acetylcholine by terminal arterioles in rat cremaster muscle

The aim of the present study was to establish whether, in terminal arterioles from the rat cremaster, acetylcholine (ACh) elicits nitric oxide (NO)-independent dilation corresponding to the transient ACh-induced endothelium-dependent hyperpolarization described in arteries. For this purpose, the responses of terminal arterioles [mean diam 15.0 +/- 0.4 (SE) microns] were studied by intravital microscopy in rat cremaster muscle. During 15 min of superfusion by 10(-5) M ACh, the response was characterized by an initial maximal dilation (peak time < 3 min) followed by a more sustained dilation that slightly decreased with time. Inhibition of NO synthesis by 2 x 10(-4) M N omega-nitro-L-arginine (L-NNA) significantly reduced, but did not eliminate, both the peak and sustained responses. Simultaneous administration of 2 x 10(-4) M L-NNA and 2 x 10(-5) M mefenamic acid, an inhibitor of prostaglandin synthesis, did not induce a significantly different response from that observed with L-NNA alone. Procaine (10(-3) M), which is known to inhibit completely ACh-induced hyperpolarization in carotid artery, drastically reduced the initial part of the ACh-induced dilation but not the sustained response. Simultaneous administration of procaine and L-NNA almost completely inhibited the peak response to ACh. Similar results were obtained when L-NNA was combined with a superfusion bath containing 20 mM KCl, a concentration known to reduce hyperpolarization in arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of nitric oxide in effects of tumor necrosis factor-alpha on microcirculation in rat

The involvement of nitric oxide (NO) in the effects of tumor necrosis factor-alpha (TNF-alpha) on the microcirculation was studied by in vivo microscopy in rat cremaster muscle. We examined second-, third-, and fourth-order arterioles with mean diameters under control conditions of 62.2, 37.4, and 16.9 microns, respectively. The vasodilation observed after topical administration of 100 ng/ml recombinant TNF-alpha (rTNF-alpha) was partly but significantly inhibited when NO synthesis was inhibited by 2 x 10(-4) M N omega-nitro-L-arginine (L-NNA). Almost complete inhibition of the acute vasodilatory effect of rTNF-alpha was found when both NO and prostaglandin synthesis were blocked by simultaneous administration of L-NNA and mefanamic acid. The effect of rTNF-alpha on vasoconstriction in response to norepinephrine (NE) was a dramatic reduction after 2 h of exposure to 1 ng/ml rTNF-alpha. Concomitant administration of 2 x 10(-4) M L-NNA prevented this hyporeactivity for second- and third-order, but not for fourth-order, arterioles. However, at 2 x 10(-3) M, L-NNA totally prevented the hyporeactivity to NE for all arteriolar orders. No changes in vasoconstriction to 70 mM KCl were observed either immediately after rTNF-alpha administration or after 2 h of exposure. We conclude that 1) the direct acute vasodilatory effect of rTNF-alpha on the microcirculation is mediated by both prostaglandins and NO, 2) long exposure to rTNF-alpha diminishes the response of the arterioles to NE but not to KCl, and 3) this effect is mediated by NO.