Attenuation of heart rate control and neural degeneration in nucleus ambiguus following chronic intermittent hypoxia in young adult Fischer 344 rats.

Chronic intermittent hypoxia (CIH) attenuates baroreflex control of heart rate (HR). In this study, we assessed whether CIH exposure reduced nucleus ambiguus (NA) control of HR and induced neural degeneration in the NA. Fischer 344 (age: 3-4 months) rats were exposed to either room air (RA: normoxia) or intermittent hypoxia for 35-50 days. At the end of these exposures, animals were anesthetized with pentobarbital. HR responses to arterial blood pressure (AP) changes induced by phenylephrine (PE) and sodium nitroprusside (SNP) were measured. In another set of rats, HR and AP responses to L-glutamate (L-Glu) microinjections (10 mM, 20 nl) into the left NA and electrical stimulation of the left cervical vagus nerve at 1-30 Hz (0.5 mA, 1 ms) for 20 s were measured. Brainstem slices at the level of -800, -400, 0, +400, +800 microm relative to the obex were processed in additional rats using Nissl staining. The NA was identified by retrogradely labeling vagal motoneurons using the tracer tetramethylrhodamine dextran (TMR-D) which was injected into the ipsilateral nodose ganglion. We found that CIH significantly 1) reduced the baroreflex control of HR (slope RA: -1.2+/-0.2 bpm/mmHg; CIH -0.5+/-0.1 bpm/mmHg; P<0.05); 2) attenuated the HR responses to l-Glu injections into the NA [HR: -280+/-15 (RA) vs. -235+/-16 (CIH) beats/min; P<0.05]; 3) augmented the HR responses to electrical stimulation of the vagus (P<0.05); 4) induced a significant cellular loss in the NA region (P<0.05). Thus, CIH induces a cell loss in the NA region which may contribute to attenuation of baroreflex sensitivity and NA control of HR following CIH.

Enhanced PKC beta II translocation and PKC beta II-RACK1 interactions in PKC epsilon-induced heart failure: a role for RACK1.

Recent investigations have established a role for the beta II-isoform of protein kinase C (PKC beta II) in the induction of cardiac hypertrophy and failure. Although receptors for activated C kinase (RACKs) have been shown to direct PKC signal transduction, the mechanism through which RACK1, a selective PKC beta II RACK, participates in PKC beta II-mediated cardiac hypertrophy and failure remains undefined. We have previously reported that PKC epsilon activation modulates the expression of RACKs, and that altered epsilon-isoform of PKC (PKC epsilon)-RACK interactions may facilitate the genesis of cardiac phenotypes in mice. Here, we present evidence that high levels of PKC epsilon activity are commensurate with impaired left ventricular function (dP/dt = 6,074 +/- 248 mmHg/s in control vs. 3,784 +/- 269 mmHg/s in transgenic) and significant myocardial hypertrophy. More importantly, we demonstrate that high levels of PKC epsilon activation induce a significant colocalization of PKC beta II with RACK1 (154 +/- 7% of control) and a marked redistribution of PKC beta II to the particulate fraction (17 +/- 2% of total PKC beta II in control mice vs. 49 +/- 5% of total PKC beta II in hypertrophied mice), without compensatory changes of the other eight PKC isoforms present in the mouse heart. This enhanced PKC beta II activation is coupled with increased RACK1 expression and PKC beta II-RACK1 interactions, demonstrating PKC epsilon-induced PKC beta II signaling via a RACK1-dependent mechanism. Taken together with our previous findings regarding enhanced RACK1 expression and PKC epsilon-RACK1 interactions in the setting of cardiac hypertrophy and failure, these results suggest that RACK1 serves as a nexus for at least two isoforms of PKC, the epsilon-isoform and the beta II-isoform, thus coordinating PKC-mediated hypertrophic signaling.

PKCepsilon activation induces dichotomous cardiac phenotypes and modulates PKCepsilon-RACK interactions and RACK expression.

Receptors for activated C kinase (RACKs) have been shown to facilitate activation of protein kinase C (PKC). However, it is unknown whether PKC activation modulates RACK protein expression and PKC-RACK interactions. This issue was studied in two PKCepsilon transgenic lines exhibiting dichotomous cardiac phenotypes: one exhibits increased resistance to myocardial ischemia (cardioprotected phenotype) induced by a modest increase in PKCepsilon activity (228 +/- 23% of control), whereas the other exhibits cardiac hypertrophy and failure (hypertrophied phenotype) induced by a marked increase in PKCepsilon activity (452 +/- 28% of control). Our data demonstrate that activation of PKC modulates the expression of RACK isotypes and PKC-RACK interactions in a PKCepsilon activity- and dosage-dependent fashion. We found that, in mice displaying the cardioprotected phenotype, activation of PKCepsilon enhanced RACK2 expression (178 +/- 13% of control) and particulate PKCepsilon-RACK2 protein-protein interactions (178 +/- 18% of control). In contrast, in mice displaying the hypertrophied phenotype, there was not only an increase in RACK2 expression (330 +/- 33% of control) and particulate PKCepsilon-RACK2 interactions (154 +/- 14% of control) but also in RACK1 protein expression (174 +/- 10% of control). Most notably, PKCepsilon-RACK1 interactions were identified in this line. With the use of transgenic mice expressing a dominant negative PKCepsilon, we found that the changes in RACK expression as well as the attending cardiac phenotypes were dependent on PKCepsilon activity. Our observations demonstrate that RACK expression is dynamically regulated by PKCepsilon and suggest that differential patterns of PKCepsilon-RACK interactions may be important determinants of PKCepsilon-dependent cardiac phenotypes.

PAF increases vascular permeability without increasing pulmonary arterial pressure in the rat.

In vivo pulmonary arterial catheterization was used to determine the mechanism by which platelet-activating factor (PAF) produces pulmonary edema in rats. PAF induces pulmonary edema by increasing pulmonary microvascular permeability (PMP) without changing the pulmonary pressure gradient. Rats were cannulated for measurement of pulmonary arterial pressure (Ppa) and mean arterial pressure. PMP was determined by using either in vivo fluorescent videomicroscopy or the ex vivo Evans blue dye technique. WEB 2086 was administered intravenously (IV) to antagonize specific PAF effects. Three experiments were performed: 1) IV PAF, 2) topical PAF, and 3) Escherichia coli bacteremia. IV PAF induced systemic hypotension with a decrease in Ppa. PMP increased after IV PAF in a dose-related manner. Topical PAF increased PMP but decreased Ppa only at high doses. Both PMP (88 +/- 5%) and Ppa (50 +/- 3%) increased during E. coli bacteremia. PAF-receptor blockade prevents changes in Ppa and PMP after both topical PAF and E. coli bacteremia. PAF, which has been shown to mediate pulmonary edema in prior studies, appears to act in the lung by primarily increasing microvascular permeability. The presence of PAF might be prerequisite for pulmonary vascular constriction during gram-negative bacteremia.

PKCepsilon modulates NF-kappaB and AP-1 via mitogen-activated protein kinases in adult rabbit cardiomyocytes.

We have previously shown that protein kinase C (PKC)-epsilon, nuclear factor (NF)-kappaB, and mitogen-activated protein kinases (MAPKs) are essential signaling elements in ischemic preconditioning. In the present study, we examined whether activation of PKCepsilon affects the activation of NF-kappaB in cardiac myocytes and whether MAPKs are mediators of this signaling event. Activation of PKCepsilon (+108% above control) in adult rabbit cardiomyocytes to a degree that has been previously shown to protect myocytes against hypoxic injury increased the DNA-binding activity of NF-kappaB (+164%) and activator protein (AP)-1 (+127%) but not that of Elk-1. Activation of PKCeta did not have an effect on these transcription factors. Activation of PKCepsilon also enhanced the phosphorylation activities of the p44/p42 MAPKs and the p54/p46 c-Jun NH(2)-terminal kinases (JNKs). PKCepsilon-induced activation of NF-kappaB and AP-1 was completely abolished by inhibition of the p44/p42 MAPK pathway with PD98059 and by inhibition of the p54/p46 JNK pathway with a dominant negative mutant of MAPK kinase-4, indicating that both signaling pathways are necessary. Taken together, these data identify NF-kappaB and AP-1 as downstream targets of PKCepsilon, thereby establishing a molecular link between activation of PKCepsilon and activation of NF-kappaB and AP-1 in cardiomyocytes. The results further demonstrate that both the p44/p42 MAPK and the p54/p46 JNK signaling pathways are essential mediators of this event.

Platelet-activating factor and bacteremia-induced pulmonary hypertension.

BACKGROUND: Acute lung injury is a common complication of gram-negative sepsis. Pulmonary hypertension and increased lung vascular permeability are central features of lung injury following experimental bacteremia. Platelet-activating factor is a prominent proinflammatory mediator during bacterial sepsis. Our previous studies have demonstrated that exogenous administration of platelet-activating factor (PAF) induces pulmonary edema without causing pulmonary hypertension. Interestingly, inhibition of PAF activity during Escherichia coli bacteremia prevents the development of both pulmonary hypertension and pulmonary edema. These data suggest that PAF contributes to pulmonary hypertension during sepsis, but that this is unlikely to be a direct vascular effect of PAF. The goal of the present study was to investigate the mechanism by which acute E. coli bacteremia induces pulmonary injury and to define the role that PAF plays in this injury. We hypothesized that the effects of PAF on pulmonary hypertension during bacteremia are due to the effects of PAF on other vascular mediators. Several studies suggest that PAF induces the expression of endothelin-1 (ET), a potent peptide vasoconstrictor. Further, our previous studies have implicated ET as a central mediator of systemic vasoconstriction during bacteremia. We therefore sought to assess whether ET is modulated by PAF. E. coli has also been demonstrated to increase endothelial production of nitric oxide (NO), which contributes to maintenance of basal vascular tone in the pulmonary circulation. We hypothesized that PAF might increase pulmonary vascular resistance during bacteremia by activating neutrophils, increasing expression of ET, and decreasing the tonic release of NO. Furthermore, we hypothesized that hypoxic vasoconstriction did not contribute to pulmonary vasoconstriction during the first 120 min of E. coli bacteremia. METHODS: Pulmonary artery pressure (PAP), blood pressure (BP), heart rate (HR), and arterial blood gases (ABG) were measured in anesthetized spontaneously breathing adult male Sprague-Dawley rats. E. coli (10(9) CFU/100 g body wt) was injected at t = 0, and hemodynamic data were obtained at 10-min intervals and ABG data at 30-min intervals for a total of 120 min. Sham animals were treated equally but received normal saline in place of E. coli. In treatment groups, a 2.5 mg/kg dose of WEB 2086, a PAF receptor antagonist, was administered intravenously 15 min prior to the onset of sepsis or sham sepsis. The groups were (1) intravenous E. coli (n = 5); (2) intravenous WEB 2086 pretreatment + intravenous E. coli (n = 5); (3) intravenous WEB 2086 alone (n = 5); and (4) intravenous normal saline (n = 6). Nitric oxide metabolites (NOx) and ET concentrations were assayed from arterial serum samples obtained at the end of the protocol. Lung tissue was harvested for measurement of myeloperoxidase (MPO) activity and pulmonary histology. RESULTS: E. coli bacteremia increased HR, PAP, and respiratory rate early during sepsis (within 20 min), while hypoxemia, hypotension, and hemoconcentration were not manifest until the second hour. Pretreatment with WEB 2086 completely abrogated all of these changes. E. coli bacteremia increased the activity of serum ET, lung MPO, and neutrophil sequestration in the lung parenchyma via a PAF-dependent mechanism. However, the mechanism of increased production of NO appears to be PAF independent. CONCLUSIONS: These data support the hypothesis that E. coli bacteremia rapidly induces pulmonary hypertension stimulated by PAF and mediated at least in part by endothelin-1 and neutrophil activation and sequestration in the lung. Microvascular injury with leak is also mediated by PAF during E. coli bacteremia, but the time course of resultant hypoxemia and hemoconcentration is slower than that of pulmonary hypertension. The contribution of hypoxic vasoconstriction in exacerbating pulmonary hypertension in gram-negative sepsis is probably a late

Microvascular endothelial cell control of peripheral vascular resistance during sepsis.

OBJECTIVE: To determine the endothelial-dependent control of decreased peripheral vascular resistance in skeletal muscle microvessels during evolving sepsis. MATERIALS AND INTERVENTIONS: Acute (4 hours, n=7), established (24 hours, n=7), or chronic (72 hours, n=8) infection was induced in Sprague-Dawley rats (150-175 g) by injecting Escherichia coli and Bacteroides fragilis (1 x 10(9) colony-forming units for both) into a subcutaneous sponge. Control animals were injected with an isotonic sodium chloride solution and analyzed at the same time points: (n=6-8 per group). Dilation in response to the topically applied endothelial-dependent agonist acetylcholine (ACH) (1 x 10(-9) to 1 x 10(-5) mol/L) was measured in inflow first-order (A1) and precapillary fourth-order (A4) arterioles in cremaster muscle in vivo with videomicroscopy. Acetylcholine dose-response curves were used to determine vascular reactivity by calculating the concentration of ACH necessary to elicit 50% of the maximal dilator response. MAIN OUTCOME MEASURES: In vivo reactivity of striated muscle microvessels to the dilation agonist ACH during acute, established, and chronic infection. RESULTS: A1 vessels were unresponsive to all doses of ACH at all time points. A4 vessels showed an increased dilator response during short-term treatment, which deteriorated over time to depressed dilation during chronic infection. CONCLUSIONS: Precapillary A4 vessels have increased dilator reactivity during early sepsis, which progresses to depressed levels with chronic infection. A1 microvessels remain dilated and are not substantially influenced by endothelial dilator mechanisms initiated by ACH. Maximum dilation of the large A1 vessels appears to contribute to the decrease in peripheral vascular resistance noted during systemic infection.

Mechanisms of triggered activity induction at the border zone of normal and abnormal cardiac tissue.

Ionic mechanisms that may be involved in inducing triggered activations at the border zone (BZTAs) of normal and abnormal Purkinje fiber segments were investigated. In a two-chamber bath, fibers were divided into a normal segment and segment treated with ethylenediaminetetraacetic acid to stimulate electrophysiologic alterations 24 hours after infarct. Interventions to normal segments included 1.8 mM lidocaine (n = 10), 3 x 10(-4) mM tetrodotoxin (n = 5), 10(-3) mM aconitine (n = 4), 3 mM cesium chloride (n = 7), 10(-2) mM verapamil (n = 4), and 6-8 mM (n = 7) of K+. Ethylenediaminetetraacetic acid (3.3 mM) prolonged action potentials and induced low diastolic potentials in the normal segment border zone. Tetrodotoxin, lidocaine, and high K+ levels suppressed BZTAs; cesium chloride and aconitine increased BZTAs; and verapamil did not reduce BZTAs. The finding that BZTAs were not abolished by verapamil suggests that abnormal automaticity is not a mechanism. Apparently, BZTAs depend on the Na+ inward current activated by depolarization of the membrane secondary to depolarization of adjacent cells.

Platelet-activating factor mediates pulmonary macromolecular leak following intestinal ischemia-reperfusion.

Platelet-activating factor (PAF) causes hypotension, cardiac dysfunction, increased vascular permeability, intestinal necrosis, and pulmonary microvascular injury when administered experimentally. Receptor antagonism attenuates or abolishes many of these effects in animal models of bacteremia, endotoxemia, and intestinal ischemia/reperfusion (I/R). The purpose of this study was to further examine the role of PAF in intestinal I/R-induced pulmonary injury using the PAF receptor antagonist WEB 2086. Sprague-Dawley rats were anesthetized and cannulated for measurement of mean arterial pressure, heart rate, and cardiac output. Laparotomy and thoracotomy were performed and the superior mesenteric artery was occluded for 45 min and reperfused for 120 min. Sham animals were treated similarly but without I/R. In the treatment groups, iv WEB 2086 (20 mg/kg/l cc NS) was administered as a bolus 15 min prior to reperfusion. Hemodynamic and videomicroscopic data were obtained before and during ischemia, and after reperfusion at 30-min intervals. Alveolar leak index was calculated offline via computer analysis of videomicroscopic images. Intestinal I/R caused pulmonary macromolecular leakage and hemodynamic instability. Treatment with WEB 2086 attenuated the pulmonary leak during the entire reperfusion period but improved cardiac output only during the first 30 min of reperfusion and had no effect on other hemodynamic variables. These data suggest that PAF is an important, but not the exclusive, mediator of pulmonary injury after intestinal I/R. PAF appears to play a minor role in the hemodynamic derangements observed after rat intestinal I/R.

Pentoxifylline attenuates pulmonary macromolecular leakage after intestinal ischemia-reperfusion.

OBJECTIVE: To assess the effects of pentoxifylline posttreatment on hemodynamic variables and acute pulmonary injury in the rat intestinal ischemia-reperfusion (I-R) model, using a recently developed method of fluorescent intravital pulmonary videomicroscopy. DESIGN: Anesthetized male Sprague-Dawley rats were cannulated for measurement of mean arterial pressure, heart rate, cardiac output, arterial blood gas values, and hematocrit. Rats underwent isolation of the superior mesenteric artery for intestinal I-R (45 minutes of ischemia, 120 minutes of reperfusion) and right lateral thoracotomy for pulmonary videomicroscopy. Epi-illumination fluorescent videomicroscopy was used to quantitate leakage of intravascular fluorescently labeled albumin into alveoli, while hemodynamic variables were simultaneously recorded. In the treatment groups, pentoxifylline was administered after 30 minutes of intestinal ischemia. Data (mean +/- SEM) were recorded before and during intestinal ischemia and after reperfusion at 30-minute intervals. MAIN OUTCOME MEASURE: The appearance of fluorescently labeled albumin into alveolar airspaces was quantitated off-line by computer and reported as the alveolar leak index. RESULTS: Intestinal I-R caused alveolar macromolecular leakage, marked by a 300% +/- 48% increase from baseline (P < .05) in the alveolar leak index. Intestinal I-R also produced systemic hemodynamic instability demonstrated by a decrease in the mean arterial blood pressure (-36% +/- 5% vs baseline, P < .05) and cardiac output (-42% +/- 6% vs baseline, P < .05), metabolic acidosis (final arterial pH of 7.17, P < .05 vs initial pH), and a 2.3-fold increase in the intravenous fluid requirement when compared with that in sham animals (P < .05). Treatment with pentoxifylline 30 minutes after intestinal ischemia attenuated pulmonary macromolecular leakage (P < .05 vs nontreated I-R) and reduced the decrease in cardiac output (-15% +/- 7% vs baseline, not statistically significant). Pentoxifylline treatment had no effect on the mean arterial blood pressure, heart rate, metabolic acidosis, or intravenous fluid requirement. CONCLUSIONS: Pentoxifylline reduces alveolar capillary membrane injury and subsequent protein leakage and improves cardiac output when administered after 30 minutes of intestinal ischemia. These data suggest that pentoxifylline may be a possible candidate as a future therapy for acute pulmonary dysfunction. Further studies in human patients are necessary.

Pulmonary subpleural arteriolar diameters during intestinal ischemia/reperfusion.

Adult respiratory distress syndrome (ARDS) often occurs in response to sepsis, shock, or ischemia/reperfusion (I/R) of a remote organ and is a frequent cause of mortality in the ICU patient. Pulmonary vascular resistance (PVR) increases during ARDS, yet direct observations of the pulmonary microcirculation are needed to characterize the vascular response. The purpose of this study was to quantitate the changes in hemodynamic variables, subpleural arteriolar diameters (AD), and alveolar cross-sectional areas (ACSA) during intestinal I/R-induced lung injury in rats, using a new method of in vivo videomicroscopy. Sprague-Dawley rats were anesthetized and cannulated, and superior mesenteric arteries were looped. A thoracotomy was performed with animals ventilated with air with 1 cm PEEP. Hemodynamic and videomicroscopic data were obtained before and during 45 min of SMA occlusion and after reperfusion, up to 120 min. Maximal vessel dilation was measured using topical 10(-5) M nitroprusside. The ability of vessels to constrict was confirmed by applying topical 10(-6) M endothelin-1. Intestinal I/R produced decreases in arterial pH, mean arterial pressure, and cardiac output. Despite these alterations, subpleural AD remained maximally dilated. Arterioles maintained the ability to constrict as demonstrated by the response to topical endothelin-1. ACSA did not change, indicating a uniform inflation of the lung. Using a unique method of in vivo pulmonary videomicroscopy, we have shown that AD do not change following 120 min of intestinal I/R, despite systemic hemodynamic instability. It appears that pulmonary arteriolar vasoconstriction does not contribute to increased PVR during the early phase of lung injury.

Nitric oxide mediates C5a-induced vasodilation in the small intestine.

OBJECTIVE: This study was designed to investigate the microvascular responses of the small intestine to complement C5a and to define the role of nitric oxide in the C5a-induced response. METHODS: Male Sprague-Dawley rats were anesthetized with pentobarbital, and a loop of small intestine was exteriorized and suffused with Krebs solution. The diameters of large and small arterioles of the small intestinal wall were measured with in vivo videomicroscopy following the application of experimental mediators. Four 1-hr C5a dose-response trials were performed (10(-14) M, 10(-12) M, 10(-10) M, and 10(-8) M). Then, we completed acetylcholine dose-response curves with and without N omega-nitro-L-arginine (N-Arg) to document the adequacy of nitric oxide synthase inhibition. The microvascular response to the topical application of C5a (10(-12) M) was recorded in the presence of 2 x 10(-4) M N-Arg. Additionally, experiments of C5a-induced response with N-Arg were repeated in the presence of L-arginine (L-Arg; the precursor of nitric oxide synthesis) or with systemic administration of superoxide dismutase (SOD). RESULTS: (1) C5a induces a dose-dependent vasodilation in the small intestine, and the maximal vasodilation occurs in A3 arterioles at C5a concentration of 10(-12) M; (2) N-Arg inhibits the Ach-induced vasodilation in the rat small intestine; and (3) L-Arg or SOD partially reverses the inhibitory effect of N-Arg. CONCLUSIONS: Nitric oxide mediates the C5a-induced vasodilation in small intestinal microvessels. Superoxide is, at least partially, responsible for the vasoconstrictor response to C5a in the presence of N-Arg.

Altered microvascular responses to C5a in rat striated muscle during two-kidney, one clip renovascular hypertension.

OBJECTIVE: To determine how two-kidney, one clip (2-K,1C) renovascular hypertension alters microvascular responses in rat striated muscle to complement C5a, one of the most important inflammatory mediators. METHODS: 2-K,1C hypertension was induced in male Sprague-Dawley rats. Under anesthesia with pentobarbital (50 mg/kg, intraperitoneally) the cremaster muscle microcirculatory preparation with intact neurovascular connections was studied in vivo by closed-circuit videomicroscopy. Recombinant human C5a was applied topically in the tissue bath at concentrations of 10(-12), 10(-10) and 10(-8) mol/l, consecutively. Changes in the microvessel diameters in small arterioles, large arterioles and venules were measured. RESULTS: In normotensive rats complement C5a induces a significant dilation in small arterioles at low bath concentrations (10(-12) or 10(-10) mol/l), but the dilation is attenuated at a higher concentration (10(-8) mol/l). In contrast, in 2-K,1C hypertensive rats C5a constricts small arterioles at low concentrations (< 10(-10) mol/l) but dilates them at a higher concentration (10(-8) mol/l). Large arterioles and venules have minimal responses to C5a in either normotensive or 2-K,1C hypertensive rats. CONCLUSION: 2-K,1C hypertension dramatically alters C5a-induced microvascular responses in small arterioles. The alteration might be attributable to the enhanced vasoconstrictor mechanisms and impaired vasodilator mechanisms during 2-K,1C renovascular hypertension.

In vivo effect of naftidrofuryl on 5-hydroxytryptamine-mediated constriction in rat peripheral microcirculation.

Naftidrofuryl is commonly used in treatment of peripheral vascular disease. Its vasodilator action has been partly explained by its inhibitory effect of 5-HT2 receptors on peripheral arteries in vitro. The purpose of this study was to test in vivo whether naftidrofuryl selectively inhibits 5-hydroxytryptamine (5-HT)-mediated constriction of large arterioles in the peripheral microcirculation. This constriction appears to be 5-HT2 receptor-mediated. Three separate protocols were used to test the effects of naftidrofuryl: chronic injection (15 mg/kg, i.p., twice daily for 5-6 days; n = 7), acute intravenous (i.v.) infusion (15 mg/kg over 30 min; n = 7), or topical application (5 x 10(-8) M, n = 6; 5 x 10(-7) M, n = 5; 5 x 10(-6) M, n = 5; 10(-5) M, n = 7). Male Sprague-Dawley rats (145-185 g body weight) were anesthetized with sodium pentobarbital (50 mg/kg) and the cremaster muscle was prepared for intravital video microscopy. Diameter response of arterioles (70-120 microns) to increasing concentrations of locally applied 5-HT (10(-8)-10(-4) M) was assessed. In rats receiving no drug treatment, 5-HT caused vasoconstriction of arterioles beginning at 10(-6) M and reaching approximately 40% constriction at 10(-4) M. These vasoactive responses were not altered by chronic daily doses or an acute infusion of naftidrofuryl. 5-HT responses obtained with and without naftidrofuryl applied directly into the cremaster-bath also had little effect on the arteriole response at each of the four concentrations tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Alteration of microvascular responses to serotonin in the diabetic rat.

This study examined the microvascular response to serotonin (5-hydroxytryptamine; 5-HT) in short-term streptozotocin-induced diabetic rats. 5-HT was applied topically to the neurovascularly intact and environmentally controlled cremaster muscle of the two-week diabetic rat. Intravital microscopy was used to measure the diameters of large arterioles (First-order; A1) and small arterioles (Third-order; A3), and the FITC-albumin leakage in small venules (Third-order; V3). The diabetic animals were divided into two groups based on the dilator capacity of the A3 arterioles: the Diabetic-Tone group had a dilator capacity of 98 +/- 14.5% compared to 11 +/- 4.1% for the Diabetic No-Tone animals. 5-HT caused significantly greater constriction of A1 arterioles in Diabetic-Tone animals (-40 +/- 6%) than in either the Control (-19 +/- 6%) or Diabetic No-Tone (-18 +/- 5%) animals. 5-HT dilated the A3 arterioles to a similar degree in both the Diabetic-Tone and Control groups, but the Diabetic No-Tone group did not dilate to 5-HT because the A3 arterioles in these animals possessed no basal tone. Control animals showed a large 5-HT concentration-dependent increase in leakage of albumin in V3 venules, but this response was inhibited in the Diabetic-Tone animals. The 5-HT-induced leakiness in the Diabetic No-Tone group was intermediate between the other two groups. These results show that large arteriole constriction and small venule permeability responses to 5-HT are altered early in the development of diabetes, and are different in those animals with and without basal arteriolar tone. These data suggest that streptozotocin-induced diabetes alters microvascular function in striated muscle by at least two different cellular mechanisms.

Reflex inotropic responses to distension of left atrium or pulmonary veins.

Previous investigators demonstrated that distension of the left atrium (LA) or pulmonary veins (PV) evokes reflex changes in heart rate (HR) and mean arterial blood pressure (MABP). This study was designed to determine whether stimulation of receptors in these areas could evoke reflex changes in left ventricular (LV) maximum contractility (Vmax) in anesthetized dogs. Balloons were placed in the left atrial appendage or in two right pulmonary veins to stimulate mechanoreceptors in these regions without directly altering other cardiorespiratory pressures. Distension of either the LA or PV increased LV contractility and decreased MABP. LA distension evoked a vagally mediated increase in HR when predistension HR was less than 140 beats/min but did not change HR when predistension HR was greater than 140 beats/min. Reflex changes in inotropic state and MABP were not altered by bilateral vagotomy or carotid sinus denervation. In dogs with stellate ganglia and sympathetic chains sectioned and vagi intact, PV or LA distension decreased LV contractility and MABP. Responses were eliminated when both vagal and sympathetic pathways were cut. We conclude that distension of the LA or the PV and LA junction evokes a sympathetically mediated increase in LV contractility.

Changes in left ventricular geometry during spontaneous breathing.

The purpose of these experiments was to determine the effects of a spontaneously generated inspiration on the size and shape of the left ventricle (LV) in anesthetized supine dogs. We implanted markers in the LV to establish three perpendicular axes and recorded the motion of these markers using biplane cinefluoroscopy at 60 Hz. The primary changes in LV size that accompanied inspiration occurred at end diastole (ED). The largest change in LVED dimension was a 2.46-mm narrowing of the septal-lateral wall dimension, but the apex-base dimension decreased also, by 0.74 mm. The anteroposterior dimension actually widened by 1.07 mm. The septal-lateral narrowing was caused by both a 1.0-mm narrowing of the distance between the septal marker and the apex-base axis, as well as by a 1.4-mm narrowing between the apex-base axis and the lateral wall marker. Narrowing of the septal portion seemed expected because of presumed enhanced right ventricular filling during inspiration. Narrowing of the lateral portion of the LV, while the anteroposterior dimension widened, was surprising because a change in LVEDV shape is implied. Assuming ventricular homogeneity, this change in LVED shape implies that the forces applied to the epicardial surface were not uniform. There must have been a retraction on the anterior and posterior surface that was not experienced by the lateral LV wall. The net effect of these dimensional changes of the LV at end diastole (estimated from the product of the three ED axes) was a 3.5-cm3 reduction in LVED volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Reflex cardiorespiratory responses to pulmonary vascular congestion.

The purpose of these studies was to determine the reflex responses of the cardiovascular system and central inspiratory activity caused by pulmonary vascular congestion. We used a canine preparation in which the left lung was isolated in situ and could be exposed to a variety of stimuli, including distension of the pulmonary capillaries with blood, without direct mechanical or chemical alterations on the circulation. We found that lung expansion to 30 cmH2O and stimulation of nerve endings of the left lung with capsaicin caused pronounced transient reflex bradycardia (-30 to -50 beats/min) and hypotension (-25 to -40 mmHg) and caused reflex cessation of inspiratory activity. Pressurizing the left pulmonary vessels by injecting blood in volumes sufficient to raise pulmonary transcapillary pressures to 30 mmHg caused no changes in heart rate, systemic arterial pressure, or inspiratory muscle activity. These results lead us to conclude that pulmonary vascular congestion does not stimulate pulmonary C-fibers or any other nerve endings to such a degree as to cause detectable changes in blood pressure, heart rate, or central inspiratory activity. Morphometric analysis revealed distended capillaries engorged with blood, but the alveolar wall surface area was not increased which raises the possibility that expansion of the alveolar membrane may be needed to mechanically initiate the C-fiber reflex.

Pulmonary edema in dogs fails to cause reflex responses.

Pulmonary edema has been proposed as a stimulus for pulmonary C-fibers. Stimulation of pulmonary C-fibers causes depression of cardiovascular function and either tachypnea or apnea. Our objective was to determine whether pulmonary edema, induced by either increasing pulmonary vascular permeability with alloxan or hydrostatic challenges, would elicit depression of cardiovascular function or changes in frequency of inspiratory activity. Utilizing a preparation in which the left pulmonary vessels and left airway were isolated, we monitored systemic blood pressure (BP), heart rate (HR), and diaphragm contractions (DC) in 13 anesthetized dogs. Injection of alloxan into the left pulmonary artery (LPA) produced transient decreases in HR, BP, and frequency of DC within 20 s of injection with no subsequent cardiorespiratory changes up to 5 min. These alloxan injections also caused coagulation necrosis. Generation of hydrostatic pulmonary edema in the left lung caused no changes in HR, BP, or in the frequency and amplitude of DC. We conclude that alloxan does stimulate reflex cardiorespiratory depression consistent with C-fiber stimulation, but these reflex responses are probably caused by alloxan's caustic effect and not by the resultant edema. We also conclude that pulmonary edema induced by increased hydrostatic pressure does not evoke any reflex cardiovascular responses or changes in frequency of inspiratory activity.