Recent studies demonstrate that nitric oxide (NO) serves as a physiological substrate for mammalian peroxidases [(2000) J. Biol. Chem. 275, 37524]. We now show that eosinophil peroxidase (EPO) and lactoperoxidase (LPO), peroxidases known to be enriched in airways of asthmatic subjects, function as a catalytic sink for NO, modulating its bioavailability and function. Using NO-selective electrodes and direct spectroscopic and rapid kinetic methods, we examined the interactions of NO with EPO and LPO compounds I and II and ferric forms and compared the results to those reported for myeloperoxidase. A unified kinetic model for NO interactions with intermediates of mammalian peroxidases during steady-state catalysis is presented that accommodates unique features observed with each member of the mammalian peroxidase superfamily. Potential functional consequences of peroxidase-NO interactions in asthma are investigated by utilizing organ chamber studies with tracheal rings. In the presence of pathophysiologically relevant levels of peroxidases and H(2)O(2), NO-dependent bronchodilation of preconstricted tracheal rings was reversibly inhibited. Thus, NO interaction with mammalian peroxidases may serve as a potential mechanism for modulating their catalytic activities, influencing the regulation of local inflammatory and infectious events in vivo.

Our goal was to determine the contributions of sympathetic and parasympathetic activity to entropy measures of heart rate variability (HRV). We compared our results with two commonly used methods to analyze HRV: standard deviation (SDNN) and power spectral analysis (HF norm). Beat-by-beat analysis of R-R intervals was performed in conscious dogs. The R-R intervals were analyzed with approximate entropy (ApEn) and entropy of symbolic dynamics (SymDyn) to assess the effects of reducing system complexity. This was achieved by pharmacologically inhibiting sympathetic, parasympathetic, and total autonomic nervous system regulation of heart rate. Three conditions were examined: rest, standing, and systemic hypotension. At rest or standing, sympathetic inhibition (propranolol) had no effect on ApEn or SymDyn, whereas parasympathetic (atropine) and combined (propranolol + atropine) inhibition reduced both entropy measures to near zero. Systemic hypotension reduced both entropy measures in intact dogs. When hypotension was induced after sympathetic inhibition, ApEn was increased compared with hypotension alone, whereas parasympathetic inhibition with hypotension resulted in near-zero ApEn. Changes in the entropy measures of HRV were directionally similar to changes in SDNN and HF norm. These results indicate that the entropy of R-R intervals reflects parasympathetic modulation of heart rate.

SUMMARY The hypothesis that a-adrenergic vasoconstriction could limit the extent of coronary vasodilation during spontaneous strenuous exercise was tested in normal mongrel dogs instrumented for the measurement of left circumflex coronary blood flow, aortic pressure, and left ventricular pressure. These signals were radiotelemetered at rest and during free-ranging exercise with dogs either in the unblocked condition, or after ^-receptor blockade (propranolol, 1 mg/kg), a-receptor blockade (phentolamine, 1-2 mg/kg), or combined ft-and a-receptor blockades. Heart rate was held constant by electrical stimulation throughout the exercise period. After a-receptor blockade alone, late diastolic coronary resistance decreased during exercise to a significantly lower (P < 0.01) level (0.36 ± 0.06 mm Hg/ml per min) than in the unblocked condition (0.52 ± 0.04 mm Hg/ml per min). In the presence of /9-adrenergic blockade, exercise induced insignificant increases in mean left circumflex coronary blood flow and decreases in late diastolic coronary resistance. In contrast, after pretreatment causing combined a and p blockade, both the increase (P < 0.05) in mean left circumflex coronary blood flow (22 ± 4 ml/min) and the decrease (P < 0.01) in late diastolic coronary resistance (0.35 ± 0.07 mm Hg/ml per min) during exercise were significantly greater. This enhanced coronary vascular dilation during exercise following a-receptor blockade could not be attributed to increased metabolically induced vasodilation secondary to changes in aortic pressure, heart rate, left ventricular systolic pressure, or left ventricular dP/dt. These observations strongly support the hypothesis that a receptors in the coronary circulation can act to attenuate alterations in coronary vascular resistance, even during periods of high sympathetic discharge, as occurs during severe exercise. Ore Res 45: 884-660, 1979 BECAUSE of the striking ability of the heart to match an increase in metabolic demand with an increase in nutrient supply, it has been presumed that control of the coronary circulation is primarily an intrinsic phenomenon involving the release of vasoactive metabolites from myocardial cells (Berne, 1964). In recent years, however, work by a number of investigators supports the concept that the coronary circulation is also under direct neural control. For instance, it has become increasingly apparent that sympathetic activation can result in a-adrenergic-mediated coronary vasoconstriction, which in turn can compete with metabolic vasodilator influences, and thus modulate alterations in coronary vascular resistance (Mohrman and Feigl, 1978).Although the existence of sympathetic coronary vasoconstrictor activity appears to be well documented, the physiological importance of such a mechanism remains unresolved. Previous work in Dr. Murray was a Postdoctoral Trainee, no 1 F 32 HL05478-01. Dr. Vatner was an Established Investigator of the American Heart Association.Received March 15, 1979; accepted for publication July 19, 1979. our laborator...

A B S T R A C T The effects of right ventricular hypertrophy on the overall and regional distribution of myocardial blood flow in the absence of an elevated coronary arterial driving pressure were evaluated in 18 conscious dogs subjected to a chronic pressure overload of the right ventricle induced by pulmonary artery constriction. The sustained pressure overload for duration of4-6 wk or 4-5 mo resulted in significant increases in right ventricular mass (45 and 110%, respectively) and right ventricular fiber diameter (22 and 60%, respectively). Moreover, the presence *tmoderate and severe hypertrophy was associated with marked increases in transmural blood flow per gram to the right ventricle proportional to the observed increases in mass, i.e., of 36 and 109%, respectively, from a normal value of 0.67+0.04 ml/min per g, whereas left ventricular blood flow remained unaltered from a normal value of 1.00±0.06 ml/min per g. Despite the large increases in blood flow per gram to moderately and severely hypertrophied right ventricle, no significant changes in the ratio of capillary:muscle fiber number were observed. These data suggest that the development of right ventricular hypertrophy is characterized by a sustained compensatory response of the coronary circulation to the augmented work load and mass, and that it is not associated with a proliferative response of the vasculature supplying the enlarged ventricle.

Modulation of [Ca2+]i in response to receptor activation is a critical determinant of vascular smooth muscle tone. In this study, we examined the effect of continuous stimulation of alpha 1-adrenoceptors with phenylephrine (PE) on [Ca2+]i in single pulmonary artery smooth muscle cells (PASMCs) cultured from explants of canine intrapulmonary artery. Fura 2-loaded PASMCs pretreated with propranolol (5 mumol/L) were continuously superfused with PE at 37 degrees C on the stage of an inverted fluorescence microscope, and [Ca2+]i was measured using a dual-wavelength spectrofluorometer. Resting values of [Ca2+]i were 96 +/- 4 nmol/L. PE (10 mumol/L) stimulated oscillations in [Ca2+]i at a frequency of 1.35 +/- 0.07/min, which reached a peak [Ca2+]i of 650 +/- 26 nmol/L (n = 69 cells). The oscillations lasted for > 30 minutes and were constant in amplitude and frequency. Both the amplitude and frequency of PE-induced [Ca2+]i oscillations increased in a dose-dependent (3 x 10(-8) to 10(-4) mol/L) manner. Pretreatment with the alpha 1-adrenoceptor antagonist prazosin (50 nmol/L) or removal of extracellular Ca2+ abolished the repetitive [Ca2+]i oscillations induced by PE. The voltage-operated Ca2+ channel blockers nifedipine (1 mumol/L) and verapamil (1 mumol/L) had no effect on the [Ca2+]i oscillations. In contrast, inhibition of phospholipase C with U73122 (10(-7) to 10(-5) mol/L) attenuated the oscillations in a dose-dependent fashion. The nonselective protein kinase inhibitor staurosporine (10(-9) to 10(-7) mol/L) had a minimal inhibitory effect on the oscillations. Caffeine (30 mmol/L) and thapsigargin (1 mumol/L) abolished the oscillations, whereas pretreatment with ryanodine (1 to 100 mumol/L) had no effect. In freshly dispersed PASMCs, PE (10 mumol/L) induced oscillations in [Ca2+]i similar to those observed in cultured cells, and patch-clamp experiments revealed oscillations in membrane potential. These results indicate that PE induces [Ca2+]i oscillations in PASMCs via stimulation of alpha 1-adrenoceptors coupled to phospholipase C activation. Voltage-operated Ca2+ channels and protein kinases are not required for the oscillations. The requirement for extracellular Ca2+ and intracellular Ca2+ stores indicates that both Ca2+ influx and intracellular Ca2+ release play a role in the maintenance of the oscillations.

We investigated the role of capacitative Ca(2+) entry and tyrosine kinase activation in mediating phenylephrine (PE)-induced oscillations in intracellular free Ca(2+) concentration ([Ca(2+)](i)) in canine pulmonary arterial smooth muscle cells (PASMCs). [Ca(2+)](i) was measured as the 340- to 380-nm ratio in individual fura 2-loaded PASMCs. Resting [Ca(2+)](i) was 96 +/- 4 nmol/l. PE (10 micromol/l) stimulated oscillations in [Ca(2+)](i), with a peak amplitude of 437 +/- 22 nmol/l and a frequency of 1.01 +/- 0.12/min. Thapsigargin (1 micromol/l) was used to deplete sarcoplasmic reticulum (SR) Ca(2+) after extracellular Ca(2+) was removed. Under these conditions, a nifedipine-insensitive, sustained increase in [Ca(2+)](i) (140 +/- 7% of control value) was observed when the extracellular Ca(2+) concentration was restored; i.e., capacitative Ca(2+) entry was demonstrated. Capacitative Ca(2+) entry also refilled SR Ca(2+) stores. Capacitative Ca(2+) entry was attenuated (32 +/- 3% of control value) by 50 micromol/l of SKF-96365 (a nonselective Ca(2+)-channel inhibitor). Tyrosine kinase inhibition with tyrphostin 23 (100 micromol/l) and genistein (100 micromol/l) also inhibited capacitative Ca(2+) entry to 63 +/- 12 and 85 +/- 4% of control values, respectively. SKF-96365 (30 micromol/l) attenuated both the amplitude (15 +/- 7% of control value) and frequency (50 +/- 21% of control value) of PE-induced Ca(2+) oscillations. SKF-96365 (50 micromol/l) abolished the oscillations. Tyrphostin 23 (100 micromol/l) also inhibited the amplitude (17 +/- 7% of control value) and frequency (45 +/- 9% of control value) of the oscillations. Genistein (30 micromol/l) had similar effects. Both SKF-96365 and tyrphostin 23 attenuated PE-induced contraction in isolated pulmonary arterial rings. These results demonstrate that capacitative Ca(2+) entry is present and capable of refilling SR Ca(2+) stores in canine PASMCs and may be involved in regulating PE-induced Ca(2+) oscillations. A tyrosine kinase is involved in the signal transduction pathway for alpha(1)-adrenoreceptor activation in PASMCs.

These results demonstrate that propofol causes an increase in PKC activity in rat ventricular myocytes. Propofol stimulates translocation of PKC-alpha, PKC-delta, PKC-epsilon, and PKC-zeta to distinct intracellular sites in cardiomyocytes. This may be a fundamentally important cellular mechanism of anesthesia-induced myocardial protection in the setting of ischemia-reperfusion injury.

We investigated the effects of an inhibitor of nitric oxide (NO) synthesis, N omega-nitro-L-arginine (L-NNA), on the pulmonary vascular pressure-flow relationship in chronically instrumented conscious dogs. The L-arginine analogue L-NNA (20 mg/min for 60 min iv) had no effect on the baseline pressure-flow relationship. This result indicates that tonic release of endothelium-derived relaxing factor (EDRF), which is thought to be NO or a labile NO-generating molecule, is not responsible for low resting pulmonary vasomotor tone in conscious dogs. In contrast, L-NNA caused a leftward shift in the dose-response relationship to the thromboxane mimetic U-46619, indicating that the endogenous release of EDRF modulates the pulmonary vascular response to this vasoconstrictor. Finally, after preconstriction with U-46619, L-NNA abolished the pulmonary vasodilator response to bradykinin (1-10 micrograms.kg-1.min-1) but had no effect on the pulmonary vasodilator response to sodium nitroprusside (1-10 micrograms.kg-1.min-1). Thus EDRF does not appear to tonically regulate the baseline pulmonary vascular pressure-flow relationship in conscious dogs. However, EDRF does act to attenuate the magnitude of U-46619-induced pulmonary vasoconstriction. Moreover, the pulmonary vasodilator response to bradykinin is entirely mediated by EDRF in conscious dogs.