Hiroshi Miyano

ESPVR of in situ rat left ventricle shows contractility-dependent curvilinearity

We developed a miniaturized conductance catheter for in situ rat left ventricular (LV) volumetry. After the validation study of the conductance volumetry in 11 rats, we characterized the end-systolic pressure-volume relationship (ESPVR) in 24 sinoaortic-denervated, vagotomized and urethan-anesthetized rats. Stroke volume (SV) measured with the conductance catheter correlated closely with that measured by electromagnetic flowmetry ( r > 0.95). No significant difference was found between the in situ LV end-diastolic volumes measured by conductance volumetry and postmortem morphometry; a linear regression analysis indicated that the correlation coefficient was 0.934, that the slope was not significantly different from 1, and that the intercept was not significantly different from 0. During cardiac sympathotonic conditions, the ESPVR was curvilinear. The estimated slope of ESPVR (end-systolic elastance, E es) by quadratic curve fitting at end-systolic pressure of 100 mmHg was 2,647 ± 846 mmHg/ml. Bilateral cervical and stellate ganglionectomy depressed contractility and made the ESPVR linear; a quadratic equation did not improve the fit. E es was 946 ± 55 mmHg/ml with the volume-axis ( V 0) intercept of 0.076 ± 0.007 ml. Administration of propranolol (1 mg/kg) further reduced E es (573 ± 61 mmHg/ml, P < 0.001) and increased V 0 slightly (0.091 ± 0.011 ml). We conclude that the conductance catheter method is useful for the assessment of the ESPVR of the in situ rat left ventricle and that the ESPVR displays contractility-dependent curvilinearity.We developed a miniaturized conductance catheter for in situ rat left ventricular (LV) volumetry. After the validation study of the conductance volumetry in 11 rats, we characterized the end-systolic pressure-volume relationship (ESPVR) in 24 sinoaortic-denervated, vagotomized and urethan-anesthetized rats. Stroke volume (SV) measured with the conductance catheter correlated closely with that measured by electromagnetic flowmetry (r > 0.95). No significant difference was found between the in situ LV end-diastolic volumes measured by conductance volumetry and postmortem morphometry; a linear regression analysis indicated that the correlation coefficient was 0.934, that the slope was not significantly different from 1, and that the intercept was not significantly different from 0. During cardiac sympathotonic conditions, the ESPVR was curvilinear. The estimated slope of ESPVR (end-systolic elastance, Ees) by quadratic curve fitting at end-systolic pressure of 100 mmHg was 2,647 +/- 846 mmHg/ml. Bilateral cervical and stellate ganglionectomy depressed contractility and made the ESPVR linear; a quadratic equation did not improve the fit. Ees was 946 +/- 55 mmHg/ml with the volume-axis (V0) intercept of 0.076 +/- 0.007 ml. Administration of propranolol (1 mg/kg) further reduced Ees (573 +/- 61 mmHg/ml, P < 0.001) and increased V0 slightly (0.091 +/- 0.011 ml). We conclude that the conductance catheter method is useful for the assessment of the ESPVR of the in situ rat left ventricle and that the ESPVR displays contractility-dependent curvilinearity.

New simple methods for isolating baroreceptor regions of carotid sinus and aortic depressor nerves in rats

We developed new methods for isolating in situ baroreceptor regions of carotid sinus and aortic depressor nerves in halothane-anesthetized rats. After ligation of the root of the external carotid artery, the internal carotid and pterygopalatine arteries were embolized with two ball bearings of 0.8 mm in diameter. Bilateral carotid sinus pressures were changed between 60 and 180 mmHg in 20-mmHg steps lasting 1 min each. The sigmoidal steady-state relationship between aortic and carotid sinus pressures in 11 rats indicated the maximum gain of the carotid sinus baroreflex to be -2.99 ± 0.75 at 120 ± 5 mmHg. An in situ isolation of the baroreceptor area of the right aortic depressor nerve could be made by ligation of the innominate, common carotid, and subclavian arteries in 9 rats. Pressure imposed on the subclavian baroreceptor was altered between 40 and 180 mmHg in 20-mmHg steps lasting 1 min each. The sigmoidal steady-state relationship between the aortic depressor nerve activity and imposed pressure showed that the baroreceptor gain peaked at 118 ± 4 mmHg. We established an easy approach to the rat baroreflex and baroreceptor research.We developed new methods for isolating in situ baroreceptor regions of carotid sinus and aortic depressor nerves in halothane-anesthetized rats. After ligation of the root of the external carotid artery, the internal carotid and pterygopalatine arteries were embolized with two ball bearings of 0.8 mm in diameter. Bilateral carotid sinus pressures were changed between 60 and 180 mmHg in 20-mmHg steps lasting 1 min each. The sigmoidal steady-state relationship between aortic and carotid sinus pressures in 11 rats indicated the maximum gain of the carotid sinus baroreflex to be -2. 99 +/- 0.75 at 120 +/- 5 mmHg. An in situ isolation of the baroreceptor area of the right aortic depressor nerve could be made by ligation of the innominate, common carotid, and subclavian arteries in 9 rats. Pressure imposed on the subclavian baroreceptor was altered between 40 and 180 mmHg in 20-mmHg steps lasting 1 min each. The sigmoidal steady-state relationship between the aortic depressor nerve activity and imposed pressure showed that the baroreceptor gain peaked at 118 +/- 4 mmHg. We established an easy approach to the rat baroreflex and baroreceptor research.

Lack of Increased Coronary Atherosclerotic Risk Due to Elevated Lipoprotein(a) in Women ≥55 Years of Age

BACKGROUNDnNumerous studies have indicated that there is an association between lipoprotein(a) [Lp(a)] and coronary artery disease (CAD) in middle-aged men; however, few studies have addressed this issue in women or the elderly.nnnMETHODS AND RESULTSnSerum Lp(a) concentrations were determined in 354 women and 706 men with or without angiographically defined CAD (one or more coronary arteries with narrowing of > or = 75%). The age-specific impact of elevated Lp(a) (> or = 30 mg/dL) on CAD was examined in each sex. In the younger age group (< 55 years old), elevated Lp(a) was independently associated with CAD in both sexes (adjusted odds ratio [OR]: women, 6.90, P < .01; men, 2.63, P < .05). The age-specific ORs declined with age, and elevated Lp(a) no longer conferred an increased CAD risk in either elderly men or women > or = 65 years old. In the age group of 55 to 64 years, elevated Lp(a) was positively associated with CAD for men (adjusted OR: 2.45, P < .05) but not for women (adjusted OR: 0.56, P = NS).nnnCONCLUSIONSnFor both sexes, elevated Lp(a) appears to be an independent risk factor for premature CAD and the importance of Lp(a) appears to decrease with age. However, for women, the risk estimate of Lp(a) began to decline at an age approximately 10 years younger than for men. These data suggest that not only age- but also sex-specific factors such as menstrual status may interact with the association between Lp(a) and CAD.

Increased Brain Angiotensin Receptor in Rats With Chronic High-Output Heart Failure

BACKGROUNDnThe renin-angiotensin system (RAS) plays a key role in the pathophysiology of chronic heart failure (CHF). In rats, we reported that CHF enhances dipsogenic responses to centrally administered angiotensin I, and central inhibition of the angiotensin-converting enzyme (ACE) prevents cardiac hypertrophy in CHF. This suggests that the brain RAS is activated in CHF. To clarify the mechanism of the central RAS activation in CHF, we examined brain ACE and the angiotensin receptor (AT) among rats with CHF.nnnMETHODS AND RESULTSnWe created high-output heart failure in 22 male Sprague-Dawley rats by aortocaval shunt. Four weeks after surgery, we examined ACE mRNA by reverse transcriptase polymerase chain reaction (RT-PCR) and AT by binding autoradiography. ACE mRNA levels were not significantly increased in the subfornical organ (SFO), the hypothalamus, or in the lower brainstem of CHF rats (n = 5) compared with sham-operated rats (SHM) (n = 6). Binding densities for type 1 AT (AT1) in the SFO (P < .05), paraventricular hypothalamic nuclei (P < .05), and solitary tract nuclei (P < .05) were higher in rats with CHF (n = 5) than in SHM rats (n = 6). Thus, in rats with CHF, AT1 expression is increased in brain regions that are closely related to water intake, vasopressin release, and hemodynamic regulation.nnnCONCLUSIONSnThe fact that AT1 expression was upregulated in important brain regions related to body fluid control in CHF rats indicates that the brain is a major site of RAS action in CHF rats and, therefore, a possible target site of ACE-inhibitors in the treatment of CHF.

Dynamic transduction properties of in situ baroreceptors of rabbit aortic depressor nerve

We developed a new method for isolating in situ baroreceptor regions of the rabbit aortic depressor nerve (ADN) and estimated the transfer function from pressure to afferent nerve activity in the frequency range of 0.01-5 Hz by a white noise technique. Complete isolation of the baroreceptor area of the right ADN was made in situ by ligation of the innominate artery and the right subclavian and common carotid arteries. We altered the pressure in the isolated baroreceptor area according to a binary quasi-white noise between 80 and 100 mmHg in 12 urethan-anesthetized rabbits. The gain increased two to three times as the frequency of pressure perturbation increased from 0.01 to 2 Hz and then decreased at higher frequencies. The phase slightly led below 0.2 Hz. The squared coherence value was > 0.8 in the frequency range of 0.01-4 Hz. The step responses estimated from the transfer function were indistinguishable from those actually observed. We conclude that the baroreceptor transduction of the ADN is governed by linear dynamics under the physiological operating pressure range.

Dynamic sympathetic regulation of left ventricular contractility studied in the isolated canine heart

We investigated the dynamic sympathetic regulation of left ventricular end-systolic elastance (Ees) using an isolated canine ventricular preparation with functioning sympathetic nerves intact. We estimated the transfer function from both stellate ganglion stimulation to Ees and ganglion stimulation to heart rate (HR) for both left and right ganglia by means of the white noise approach and transformed those transfer functions into corresponding step responses. The HR response was much larger with right sympathetic stimulation than with left sympathetic stimulation (4.3 +/- 1.4 vs. 0.7 +/- 0.6 beats . min-1 . Hz-1, P < 0.01). In contrast, the Ees responses without pacing were not significantly different between left and right sympathetic stimulation (0.72 +/- 0.34 vs. 0.76 +/- 0. 42 mmHg . ml-1 . Hz-1). Fixed-rate pacing significantly decreased the Ees response to right sympathetic stimulation (0.53 +/- 0.43 mmHg . ml-1 . Hz-1, P < 0.01), but not to left sympathetic stimulation (0.67 +/- 0.32 mmHg . ml-1 . Hz-1, not significant). Although the mechanism by which the sympathetic nervous system regulates cardiac contractility is different depending on whether the left or right sympathetic nerves are activated, this difference does not affect the apparent response of Ees to dynamic sympathetic stimulation.We investigated the dynamic sympathetic regulation of left ventricular end-systolic elastance ( E es) using an isolated canine ventricular preparation with functioning sympathetic nerves intact. We estimated the transfer function from both stellate ganglion stimulation to E es and ganglion stimulation to heart rate (HR) for both left and right ganglia by means of the white noise approach and transformed those transfer functions into corresponding step responses. The HR response was much larger with right sympathetic stimulation than with left sympathetic stimulation (4.3 ± 1.4 vs. 0.7 ± 0.6 beats ⋅ min-1 ⋅ Hz-1, P < 0.01). In contrast, the E es responses without pacing were not significantly different between left and right sympathetic stimulation (0.72 ± 0.34 vs. 0.76 ± 0.42 mmHg ⋅ ml-1 ⋅ Hz-1). Fixed-rate pacing significantly decreased the E es response to right sympathetic stimulation (0.53 ± 0.43 mmHg ⋅ ml-1 ⋅ Hz-1, P < 0.01), but not to left sympathetic stimulation (0.67 ± 0.32 mmHg ⋅ ml-1 ⋅ Hz-1, not significant). Although the mechanism by which the sympathetic nervous system regulates cardiac contractility is different depending on whether the left or right sympathetic nerves are activated, this difference does not affect the apparent response of E es to dynamic sympathetic stimulation.

Cholinesterase affects dynamic transduction properties from vagal stimulation to heart rate

Recent investigations in our laboratory using a Gaussian white noise technique showed that the transfer function representing the dynamic properties of transduction from vagus nerve activity to heart rate had characteristics of a first-order low-pass filter. However, the physiological determinants of those characteristics remain to be elucidated. In this study, we stimulated the vagus nerve according to a Gaussian white noise pattern to estimate the transfer function from vagal stimulation to the heart rate response in anesthetized rabbits and examined how changes in acetylcholine kinetics affected the transfer function. We found that although increases in the mean frequency of vagal stimulation from 5 to 10 Hz did not change the characteristics of the transfer function, administration of neostigmine (30 microg . kg-1 . h-1 iv), a cholinesterase inhibitor, increased the dynamic gain from 8.19 +/- 3.66 to 11.7 +/- 4.88 beats . min-1 . Hz-1 (P < 0.05), decreased the corner frequency from 0.12 +/- 0.05 to 0.04 +/- 0.01 Hz (P < 0.01), and increased the lag time from 0.17 +/- 0.12 to 0.27 +/- 0.08 s (P < 0.05). These results suggest that the rate of acetylcholine degradation at the neuroeffector junction, rather than the amount of available acetylcholine, plays a key role in determining the dynamic properties of transduction from vagus nerve activity to heart rate.Recent investigations in our laboratory using a Gaussian white noise technique showed that the transfer function representing the dynamic properties of transduction from vagus nerve activity to heart rate had characteristics of a first-order low-pass filter. However, the physiological determinants of those characteristics remain to be elucidated. In this study, we stimulated the vagus nerve according to a Gaussian white noise pattern to estimate the transfer function from vagal stimulation to the heart rate response in anesthetized rabbits and examined how changes in acetylcholine kinetics affected the transfer function. We found that although increases in the mean frequency of vagal stimulation from 5 to 10 Hz did not change the characteristics of the transfer function, administration of neostigmine (30 μg ⋅ kg-1 ⋅ h-1iv), a cholinesterase inhibitor, increased the dynamic gain from 8.19 ± 3.66 to 11.7 ± 4.88 beats ⋅ min-1 ⋅ Hz-1( P < 0.05), decreased the corner frequency from 0.12 ± 0.05 to 0.04 ± 0.01 Hz ( P < 0.01), and increased the lag time from 0.17 ± 0.12 to 0.27 ± 0.08 s ( P < 0.05). These results suggest that the rate of acetylcholine degradation at the neuroeffector junction, rather than the amount of available acetylcholine, plays a key role in determining the dynamic properties of transduction from vagus nerve activity to heart rate.

Simultaneous identification of static and dynamic vagosympathetic interactions in regulating heart rate

We earlier reported that stimulation of either one of the sympathetic and vagal nerves augments the dynamic heart rate (HR) response to concurrent stimulation of its counterpart. We explained this phenomenon by assuming a sigmoidal static relationship between nerve activity and HR. To confirm this assumption, we stimulated the sympathetic and/or vagal nerve in anesthetized rabbits using large-amplitude Gaussian white noise and determined the static and dynamic characteristics of HR regulation by a neural network analysis. The static characteristics approximated a sigmoidal relationship between the linearly predicted and the measured HRs (response range: 212.4 ± 46.3 beats/min, minimum HR: 96.0 ± 28.4 beats/min, midpoint of operation: 196.7 ± 31.3 beats/min, maximum slope: 1.65 ± 0.51). The maximum step responses determined from the dynamic characteristics were 7.9 ± 2.9 and -14.0 ± 4.9 beats ⋅ min-1 ⋅ Hz-1for the sympathetic and the vagal system, respectively. Because of these characteristics, changes in sympathetic or vagal tone alone can alter the dynamic HR response to stimulation of the other nerve.We earlier reported that stimulation of either one of the sympathetic and vagal nerves augments the dynamic heart rate (HR) response to concurrent stimulation of its counterpart. We explained this phenomenon by assuming a sigmoidal static relationship between nerve activity and HR. To confirm this assumption, we stimulated the sympathetic and/or vagal nerve in anesthetized rabbits using large-amplitude Gaussian white noise and determined the static and dynamic characteristics of HR regulation by a neural network analysis. The static characteristics approximated a sigmoidal relationship between the linearly predicted and the measured HRs (response range: 212.4 +/- 46.3 beats/min, minimum HR: 96.0 +/- 28.4 beats/min, midpoint of operation: 196.7 +/- 31.3 beats/min, maximum slope: 1.65 +/- 0.51). The maximum step responses determined from the dynamic characteristics were 7.9 +/- 2.9 and -14.0 +/- 4.9 beats. min-1. Hz-1 for the sympathetic and the vagal system, respectively. Because of these characteristics, changes in sympathetic or vagal tone alone can alter the dynamic HR response to stimulation of the other nerve.

Effectiveness of LDL-apheresis in preventing restenosis after percutaneous transluminal coronary angioplasty (PTCA): LDL-apheresis angioplasty restenosis trial (L-ART)

To investigate the efficacy of reducing plasma lipoprotein(a) (Lp(a)) as well as low density lipoprotein cholesterol (LDL-C) levels on the prevention of restenosis after PTCA, LDL-apheresis was attempted on a total of 54 patients at six institutions. LDL-apheresis using a dextran sulfate cellulose column has been proven to be an effective method for reducing both plasma Lp(a) and LDL-C levels. As a subgroup (apheresis-drug combined group), 29 of the 54 patients were given Pravastatin (HMG CoA reductase inhibitor) and Niceritrol (Nicotinic Acid) in addition to LDL-apheresis to maintain low plasma levels of both Lp(a) and LDL-C through the follow-up period of 5 months after PTCA. Patients whose plasma Lp(a) levels were reduced by more than 50% showed a lower restenosis rate than those whose plasma Lp(a) levels were reduced by less than 50% (21.2% vs. 52.4%, P = 0.0179), especially in patients with high plasma Lp(a) levels above 30 mg/dl where a much lower restenosis rate (15.0%) was observed. Furthermore, in the apheresis-drug combined group, the restenosis rate was 11.8% regardless of baseline plasma Lp(a) levels, including even those below 30 mg/dl. In conclusion, in patients with high plasma Lp(a) levels, a greater than 50% reduction in Lp(a) levels by LDL-apheresis is effective in preventing restenosis after PTCA. If the plasma Lp(a) reduction rate is greater than 50%, LDL-apheresis combined with lipid-lowering drugs such as niceritrol and pravastatin seems to be more effective, even in patients with low plasma Lp(a) levels.

Neuronal uptake affects dynamic characteristics of heart rate response to sympathetic stimulation

Recently, studies in our laboratory involving the use of a Gaussian white noise technique demonstrated that the transfer function from sympathetic stimulation frequency to heart rate (HR) response showed dynamic characteristics of a second-order low-pass filter. However, determinants for the characteristics remain to be established. We examined the effect of an increase in mean sympathetic stimulation frequency and that of a blockade of the neuronal uptake mechanism on the transfer function in anesthetized rabbits. We found that increasing mean sympathetic stimulation frequency from 1 to 4 Hz significantly ( P < 0.01) decreased the dynamic gain of the transfer function without affecting other parameters, such as the natural frequency, lag time, or damping coefficient. In contrast, the administration of desipramine (0.3 mg/kg iv), a neuronal uptake blocking agent, significantly ( P < 0.01) decreased both the dynamic gain and the natural frequency and prolonged the lag time. These results suggest that the removal rate of norepinephrine at the neuroeffector junction, rather than the amount of available norepinephrine, plays an important role in determining the low-pass filter characteristics of the HR response to sympathetic stimulation.Recently, studies in our laboratory involving the use of a Gaussian white noise technique demonstrated that the transfer function from sympathetic stimulation frequency to heart rate (HR) response showed dynamic characteristics of a second-order low-pass filter. However, determinants for the characteristics remain to be established. We examined the effect of an increase in mean sympathetic stimulation frequency and that of a blockade of the neuronal uptake mechanism on the transfer function in anesthetized rabbits. We found that increasing mean sympathetic stimulation frequency from 1 to 4 Hz significantly (P < 0.01) decreased the dynamic gain of the transfer function without affecting other parameters, such as the natural frequency, lag time, or damping coefficient. In contrast, the administration of desipramine (0.3 mg/kg iv), a neuronal uptake blocking agent, significantly (P < 0.01) decreased both the dynamic gain and the natural frequency and prolonged the lag time. These results suggest that the removal rate of norepinephrine at the neuroeffector junction, rather than the amount of available norepinephrine, plays an important role in determining the low-pass filter characteristics of the HR response to sympathetic stimulation.