Mitsumasa Keitoku

Modification of myogenic intrinsic tone and [Ca2+]i of rat isolated arterioles by ryanodine and cyclopiazonic acid.

The role of the sarcoplasmic reticulum (SR) in regulating myogenic tone and [Ca2+]i was examined with ryanodine and cyclopiazonic acid (CPA) in the rat skeletal muscle arteriole (A(sk)) and mesenteric arteriole (Ams). Arterioles were cannulated at both ends to control luminal pressure in a tissue bath. Luminal diameter was measured with a video-monitored microscopic system. Fura 2-AM was loaded to measure [Ca2+]i using the fluorescence intensity ratio at excitation wavelengths of 340 to 380 nm (F340/380). The myogenic response (luminal pressure was increased from 40 to 100 mm Hg) and the intrinsic tone at 40 mm Hg were observed in A(sk) but not in Ams. Ryanodine (10(-5) M decreased the steady-state diameter of A(sk) from 138 +/- 8 to 85 +/- 9 microns (P < .05) and increased the F340/380 ratio; these effects were reversed by nifedipine or Ca(2+)-free solution. Ryanodine shifted the [Ca2+]o-contraction response curve upward. CPA (10(-5) M) also decreased the steady-state diameter of A(sk) from 131 +/- 7 to 98 +/- 11 microns (P < .05). In contrast, Ams responded to neither ryanodine nor CPA. Caffeine-induced contractions were significantly reduced by either ryanodine or CPA in both arterioles. These results indicate that SR dysfunction increased the susceptibility of the arteriolar tone to [Ca2+]o and enhanced the tone of A(sk). In conclusion, the SR function may play a critical role in regulating [Ca2+]i and the intrinsic tone of A(sk) that was myogenically active at physiological luminal pressure.

Influences of pressure surrounding the heart and intracardiac pressure on the diastolic coronary pressure-flow relation in excised canine heart.

We investigated the change in the instantaneous diastolic left coronary pressure-flow relation (DPFR) when the pressure surrounding the heart (SHP), right heart pressure (RHP), and left heart pressure (LHP) were systematically varied. Eight excised and maximally vasodilated canine hearts placed in an air-tight chamber were used. To obtain a capacitance-free DPFR, coronary perfusion pressure was slowly decreased (about 2 mm Hg/sec) during a prolonged diastole. The zero-flow pressure (Pf = 0) and the slope of the DPFR were analyzed. The mean values of the slope did not change significantly throughout the interventions. The mean value of Pf=0 in the control state (SHP = RHP = LHP = 0 mm Hg) was 6.0 ± 2.0 mm Hg (mean ± SD, n = 8), significantly higher than the venous outflow pressure, RHP (p<0.001), and the other two pressures (p<0.001). When SHP was raised to 15 and 30 mm Hg, while the other pressures remained at 0 mm Hg, the mean values of Pf=0 increased to 20.9 ± 2.4 and 35.6 ± 3.1 mm Hg (p<0.001 and p<0.0005, respectively, vs. control). The mean values of Pf =0 when only RHP was elevated to 15 and 30 mm Hg were 16.0 ± 1.5 and 29.3 ± 1.5 mm Hg (p<0.001 and p<0.0005 vs. control). On elevation of LHP to 15 and 30 mm Hg, the mean values of Pf = 0 were 12.0 ± 2.8 and 17.3 ± 3.6 mm Hg (p<0.01 and p<0.01 vs. control). When both SHP and LHP were almost evenly elevated to about 15 and 30 mm Hg, the mean values of Pf = 0 were raised to 22.0 ± 2.9 and 35.3 ± 3.2 mm Hg, respectively. These mean values were not significantly different from those when only SHP was elevated to the comparable levels. The observation that Pf = 0 exceeded RHP in the control state and that RHP, which was elevated above the preceding Pf=0, was identical with the present Pf=0 supports the vascular waterfall mechanism when RHP is low. Furthermore, the evidence that the degree of DPFR shift was almost linearly dependent on the SHP level rather than on the LHP level indicates that the pressure on the epicardial side is one of the factors that determines the pressure at the top of the vascular waterfall.

Effects of OPC-8212, a new positive inotropic agent, and dobutamine on left ventricular global and ischemic regional functions and coronary hemodynamics under coronary artery stenosis

Summary: We have investigated the effects of OPC-8212, a new positive inotropic agent, and dobutamine, a known cardioselective inotropic agent, on global left ventricular (LV) and ischemic regional functions in 14 excised canine hearts with a flow-limiting stenosis of the left circumflex coronary artery (LCX) (i.e., 20–25% of control flow). OPC-8212 infusion (n = 7) under LCX stenosis improved cardiac depression [i.e., peak LV dP/dt increased from 1,295 ± 143 mm Hg/s to 2,669 ± 266 mm Hg/s (mean ± SEM) (p < 0.001)], while myocardial ischemic injury, assessed by myocardial CO2-tension and electrocardiogram (ECG)-ST changes, improved (i.e., ΔCO2-tension and ECG-ST deviation decreased from 21.1 ± 3.6 mm Hg and 3.8 ± 0.6 mV to 13.3 ± 2.8 mm Hg (p < 0.01) and 2.0 ± 0.7 mV (p < 0.05), respectively). On the other hand, dobutamine infusion (n = 7) further increased myocardial CO2-tension and ECG-ST deviation [i.e., ΔCO2-tension and ECG-ST deviation increased from 14.4 ± 4.2 mm Hg and 2.5 ± 1.2 mV to 29.0 ± 6.0 mm Hg (p < 0.01) and 4.9 ± 1.0 mV (p < 0.01), respectively]. At the same time, peak LV dP/dt clearly improved, but to a lesser degree; from 1,425 ± 153 mm Hg/s to 2,393 ± 245 mm Hg/s (p < 0.001). There was also an increase in percent systolic segment shortening of each corresponding area as with OPC-8212. As a result, the two inotropic drugs had different effects on ΔCO2-tension (p < 0.0001) and ECG-ST deviation (p < 0.0006) in the ischemic region. Thus, this new drug, OPC-8212, seems to be potentially useful in the management of heart failure induced or accompanied by ischemic heart disease.

Unstimulated polymorphonuclear neutrophils regulate proximal coronary arterial tone

Our objective is to clarify, by measuring the superoxide production as a marker of inactive state of polymorphonuclear neutrophils, whether unstimulated polymorphonuclear neutrophils would influence coronary arterial tone. We recorded the isometric tension of the porcine coronary arterial ring in a bath of oxygenated Krebs Ringer solution. Unstimulated porcine polymorphonuclear neutrophils that contained little superoxide were added to the bath. We also analyzed the prostaglandins produced in the bath. The isometric tension of arterial rings increased dose-dependently when polymorphonuclear neutrophils were added to the bath. The vasoconstriction induced by unstimulated polymorphonuclear neutrophils was inhibited by endothelial denudation, indomethacin, anti-CD11a/18-like antibody. Thromboxane A2 synthetase inhibitor and superoxide dismutase did not effect the vasoconstriction. Prostaglandin E2 predominated among the prostaglandins produced in the bath; its production was significantly inhibited by indomethacin (without vs. with indomethacin; 3898 +/- 1704 vs 1956 +/- 715 pg/ml, P < 0.05, n=6). Pretreatment of vascular rings with indomethacin blocked the interaction of the coronary artery with polymorphonuclear neutrophils. Results suggested that unstimulated polymorphonuclear neutrophils constrict the proximal coronary artery. Such vasoconstriction may be produced by cyclooxygenase products, especially prostaglandin E2 produced in the vascular wall via the interaction between the polymorphonuclear neutrophils and the endothelium. Polymorphonuclear neutrophils may regulate coronary arterial tone.

Contraction and Relaxation Responses to fMLP in Isolated Human Coronary Arteries

The intimal thickening commonly found in human coronary arteries involves macrophage infiltration; this may contribute to the development of local vascular tone. We investigated the effects of the leukocyte stimulant, N-formyl-L-methionyl- L-leucyl-L-phenylalanine (fMLP), on human coronary arterial tone. For isometric tension recording, isolated human coronary arterial rings were suspended in a tissue bath filled with Krebs-Ringer solution. A single dose of fMLP (10−5M) was added to rings precontracted with 10−5M phenylephrine. Tension changes in response to fMLP were expressed as percentages of maximum potassium contraction or maximum papaverine relaxation. The inhibitors used were pretreated 15min before the addition of phenylephrine. In parallel, coronary segments were histologically examined for identifying the infiltrated inflammatory cells. In most cases examined, fMLP at 10−5M produced biphasic tension changes, with rapid contraction followed by relaxation (60±9%/–52±10%). Removal of the endothelium or adventitia did not alter the responses to fMLP. The contraction phase was nearly abolished by the thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor blocker, ONO3708 (10−6M; 0%/–72±12%), and the selective TXA2 synthetase inhibitor, DP-1904 (10−5M; 11 ±4%/–55± 11 %). Indomethacin (2 × 10−5M) inhibited both phases, but the contraction remained small (11 ± 4%). However, the selective PGI2 synthetase inhibitor tranylcypromine (10−4M) did not reduce the relaxation phase in the presence of ONO3708 (−49 ± 15%).