bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential effects of antihypertensive drug therapy on vascular smooth muscle cell hypertrophy, hyperploidy, and hyperplasia in the spontaneously hypertensive rat.
Authors: Owens G K
Published: June 2012

The present report extends our previous studies of smooth muscle cell hypertrophy, hyperploidy, and hyperplasia in the 5-month-old spontaneously hypertensive and Wistar-Kyoto rats to include analyses of 3- and 7-month-old rats and explores the effects of antihypertensive drug treatment on the accelerated growth of vascular smooth muscle in aortas of spontaneously hypertensive vs. Wistar-Kyoto rats. Drug-treated rats were administered a combination of reserpine, hydralazine, and chlorathiazide in their drinking water, either between 3 and 5 months or between 5 and 7 months of age. Drug treatment decreased the blood pressure of spontaneously hypertensive rats to values at or below those of Wistar-Kyoto rats for both age-treatment groups. Smooth muscle growth was evaluated by morphometric analyses of aortic smooth muscle content, flow cytometric and microdensitometric measurements of the frequency of polyploid smooth muscle cells, biochemical estimates of aortic medial smooth muscle cell number, and microdensitometric measurements of individual smooth muscle cell protein content. The following results were obtained. Aortic medial smooth muscle content was not significantly increased in 3-month spontaneously hypertensive compared to Wistar-Kyoto rats, indicating that aortic smooth muscle hypertrophy occurred post-3 months, as well as after blood pressure was elevated. In 5-month-old spontaneously hypertensive and Wistar-Kyoto rats, medial smooth muscle hypertrophy could be accounted for by cellular hypertrophy without hyperplasia; in contrast, medial hypertrophy in 7-month-old spontaneously hypertensive rats involved both cellular hypertrophy and hyperplasia. Antihypertensive treatment prevented the accelerated growth of vascular smooth muscle that occurred in spontaneously hypertensive rats via cellular hypertrophy and hyperploidy, but it did not prevent an increase in smooth muscle cell number in spontaneously hypertensive rats between 5 and 7 months of age. Furthermore, it had no effect on the parallel increases in aortic medial smooth muscle cell number that occurred in both spontaneously hypertensive and Wistar-Kyoto rats between 3 and 5 months of age. Whereas drug treatment prevented accelerated development of smooth muscle cell polyploidism in spontaneously hypertensive rats, in no case (spontaneously hypertensive or Wistar-Kyoto rats) did it reverse changes in ploidy that existed at the time of initiation of drug treatment, although it did cause cellular atrophy in smooth muscle cells of each ploidy class.(ABSTRACT TRUNCATED AT 400 WORDS)
Rate-related suppression and facilitation of conduction in isolated canine cardiac Purkinje fibers.
Authors: Gilmour R F , Salata J J , Zipes D P
Published: June 2012

Previous studies have shown that antegrade conduction through damaged His Purkinje tissue may be suppressed following rapid ventricular pacing (overdrive suppression of conduction). We studied this phenomenon using isolated Purkinje fibers placed in a three-chamber bath. Superfusates for the left, middle, and right segments of the fiber were altered to produce action potentials that resembled those of normal bundle branch, damaged His bundle, and normal His bundle, respectively. To produce anisotropic conduction, the left segment of the fiber was adjusted to be three to four times longer than the right segment. Pacing the right segment at intermediate rates produced maximal action potential amplitude in the middle segment and 1:1 right-to-left conduction, whereas pacing at faster or slower rates reduced action potential amplitude and produced block. Pacing the left segment at fast or slow rates also reduced action potential amplitude in the middle segment, but conduction was maintained (anisotropy). After rapid or slow left segment pacing, action potential amplitude in the middle segment remained low during subsequent right segment pacing at intermediate rates, and transient block occurred (overdrive or underdrive suppression of conduction). With time, action potential amplitude normalized and conduction resumed. In other more severely depressed preparations, conduction block occurred even at intermediate right segment pacing rates prior to left segment pacing. Under these conditions, pacing the left segment at intermediate rates increased action potential amplitude in the middle segment and temporarily permitted 1:1 conduction at intermediate right segment pacing rates (overdrive facilitation of conduction).(ABSTRACT TRUNCATED AT 250 WORDS)
Role of afterload in determining regional right ventricular performance during coronary underperfusion in dogs.
Authors: Urabe Y , Tomoike H , Ohzono K , Koyanagi S , Nakamura M
Published: June 2012

The relationship between coronary perfusion pressure and regional myocardial performance of the right ventricular free wall was studied, in the presence or absence of right ventricular hypertension in 13 open-chest dogs. The right coronary artery was perfused through a shunt from a carotid artery. Regional systolic shortening of the right ventricular free wall was measured by means of a sonomicrometric technique at various levels of coronary perfusion pressure. Regional shortening was insensitive to coronary perfusion pressure or flow when it was above 31 mm Hg or 0.27 ml/min per g. Once coronary perfusion was below this critical level, regional shortening in both base to apex and circumferential orientations decreased linearly, depending on the degree of perfusion pressure. Despite the presence of a monoexponential relationship between coronary perfusion pressure or flow and regional shortening, a direct linear relation between perfusion pressure and flow was consistently noted, with or without pulmonary artery banding, suggesting that there is limited autoregulation of right coronary flow. The critical perfusion pressure for maintaining regional myocardial function of the right ventricle was highly dependent on the level of right ventricular systolic pressure (r = 0.64 - 0.72, P less than 0.05). Thus, right ventricular systolic pressure was one of the important determinants of regional wall motion during coronary underperfusion.
Adverse effects of chronic cardiac denervation in conscious dogs with myocardial ischemia.
Authors: Lavallee M , Amano J , Vatner S F , Manders W T , Randall W C , Thomas J X
Published: June 2012

The extent to which total chronic cardiac denervation protects the ischemic myocardium was investigated in conscious dogs. The major hemodynamic difference after coronary artery occlusion was that left ventricular end-diastolic pressure rose significantly more, P less than 0.01, in the denervated group (12 +/- 1.5 mm Hg) than in the normal group (4.4 +/- 1.4 mm Hg). Blood flow (radioactive microspheres) in the ischemic endo- and epicardium fell to similar levels at 3-5 minutes after coronary occlusion, but was significantly less (P less than 0.01) in denervated dogs at 3 hours after occlusion in the endo- (0.05 +/- 0.01) and epicardium (0.30 +/- 0.02 ml/min per g), than in the endo- (0.13 +/- 0.03) and epicardium (0.42 +/- 0.05 ml/min per g) in the normal group. A subgroup of normal dogs was also studied, with left ventricular end-diastolic pressure increased by volume loading to levels similar to those observed in the denervated group after coronary occlusion; in these dogs, blood flow was similar to that in the other two groups 3-5 minutes after coronary artery occlusion, but, at 3 hours, was significantly more depressed (P less than 0.01) than that observed in normal dogs without volume loading in both endo- (0.03 +/- 0.01) and epicardial (0.25 +/- 0.03 ml/min per g) layers. Infarct size, as a fraction of the area at risk, was significantly greater (P less than 0.05) in the denervated group (60 +/- 4.3%) and in the subgroup of normal dogs with elevated left ventricular end-diastolic pressure (73 +/- 5.8%), compared with the normal group without volume loading (37 +/- 8.1%). Thus, in conscious dogs, total chronic cardiac denervation exerts an adverse effect on infarct size which may be related to the sustained elevation in left ventricular end-diastolic pressure and consequent impairment of collateral perfusion.
Protamine inhibits capillary formation in growing rat hearts.
Authors: Rakusan K , Turek Z
Published: June 2012

Various indices of capillary supply to the rat heart were studied in neonatal rats injected for 2 or 4 weeks with protamine sulfate in saline (subcutaneously, 60 mg/kg body weight, 2 times/day). Cardiac capillarization was evaluated not only by traditional indices for the capillary supply, such as mean capillary density and myocyte-to-capillary ratio, but also by a more advanced morphometric method of capillary domains. This method allows the estimation of both the average radius of the Krogh tissue cylinder and its variability, which reflects the heterogeneity of capillary spacing found to be an independent morphological determinant of oxygen diffusion in the tissue. The results were evaluated with respect to regional differences (subendocardial vs. middle section), age differences, and the effect of protamine. No regional differences in capillary supply were found in this experimental situation. Hearts from older rats had significantly decreased capillary supply, expressed as lower capillary density, larger capillary domains, and greater radius of the tissue cylinder. On the other hand, the heterogeneity of capillary spacing decreased significantly with age. Protamine-injected animals, when compared to their control littermates, had a significantly higher cell-to-capillary ratio, lower capillary density, larger capillary domains, greater radius of the tissue cylinder, and larger variability in capillary spacing. Thus, protamine was effective in impeding rapid capillary growth in the hearts from rats in the early postnatal period. Close to half of all the existing capillaries in the adult rat hearts are formed during the first 3-4 postnatal weeks.
Neuronal regulation of the development of the alpha-adrenergic chronotropic response in the rat heart.
Authors: Drugge E D , Rosen M R , Robinson R B
Published: June 2012

During development, there are changes in the response of automatic cardiac fibers to alpha-adrenergic agonists. In neonatal rat ventricle, in vitro phenylephrine (1 X 10(-8) M) induces an increase in automatic rate from 115 +/- 12 (mean +/- SEM) to 168 +/- 10 beats/min, P less than 0.05. In contrast, in adult rat ventricle, the rate decreases from 36 +/- 8 to 12 +/- 12 beats/min, P less than 0.05. At both ages, the response is attenuated by the alpha 1-antagonist, prazosin (1 X 10(-6) M). We used cultures of neonatal rat myocytes to determine whether maturation of innervation contributes to the ontogeny of this response. All non-innervated cultures showed a positive chronotropic response to alpha-stimulation; phenylephrine (1 X 10(-8) M) increased the rate from 40 +/- 2 to 52 +/- 2 beats/min, P less than 0.05. In contrast, 60% of the myocytes innervated with sympathetic neurons showed a decrease in rate in response to phenylephrine, from 78 +/- 6 to 67 +/- 6 beats/min, P less than 0.05. The negative chronotropic effect of phenylephrine did not result from the release of acetylcholine or adenosine, or the inhibition of presynaptic norepinephrine release by phenylephrine. Furthermore, exposure to neuronal norepinephrine is not responsible for the alteration in muscle cell responsiveness. In conclusion, we have demonstrated the modulation of the myocardial response to alpha-adrenergic stimulation by the occurrence of innervation in tissue culture. This provides an explanation for the previously identified ontogenetic change in alpha-adrenergic effects on intact cardiac fibers from excitation to inhibition.
Vagal chemoreflex coronary vasodilation evoked by stimulating pulmonary C-fibers in dogs.
Authors: Clozel J P , Roberts A M , Hoffman J I , Coleridge H M , Coleridge J C
Published: June 2012

We performed experiments on anesthetized, open-chest dogs to determine whether the pulmonary chemoreflex (bradycardia and systemic hypotension) evoked by stimulating pulmonary C-fibers also involves reflex changes in coronary vascular resistance. We perfused the circumflex coronary artery at constant pressure (usually 100 mm Hg) and recorded mean circumflex blood flow. Stimulation of pulmonary C-fibers by right atrial injection of capsaicin (10 micrograms/kg) decreased arterial blood pressure and heart rate and increased circumflex blood flow by 32-109% (P less than 0.001). Circumflex blood flow also increased, by 26-100% (P less than 0.001), when heart rate was kept constant by pacing. Coronary vasodilation was not secondary to the reflex decrease in arterial blood pressure. Injecting capsaicin (10 micrograms/kg) into the left atrium did not increase circumflex blood flow. Reflex coronary vasodilation could still be evoked when myelinated nerve fibers were blocked selectively by cooling the cervical vagus nerves to 7-8 degrees C but was abolished by cooling to 0 degrees C, by cutting the pulmonary vagal branches, or by giving atropine. Reducing coronary perfusion pressure shifted the stimulus (dose of capsaicin)-response (increase in coronary blood flow) curve to the right, but, even at low perfusion pressures, significant reflex vasodilation still occurred. Regional (transmural) distribution of myocardial blood flow was measured by the microsphere technique at various perfusion pressures. The endocardial:epicardial blood flow ratio decreased significantly as perfusion pressure was reduced, but was not altered by right atrial injection of capsaicin at any perfusion pressure. Our results indicate that stimulation of pulmonary C-fibers triggers reflex cholinergic vasodilation in all layers of the myocardium.
Role of sodium in hypertensive cardiac hypertrophy.
Authors: Lindpaintner K , Sen S
Published: June 2012

Cardiac hypertrophy in systemic hypertension may not result simply from increased afterload. Previous studies indicate that factors other than blood pressure may influence cardiac hypertrophy. We evaluated the effects of dietary sodium restriction in two-kidney one-clip renal hypertensive rats. After the renal artery had been clipped, the rats received a normal diet until hypertension was established; thereafter, a sodium-deficient diet was instituted in one group. Clipped rats on a regular diet had significantly higher systolic blood pressures than sham-operated controls (205 +/- 9 vs. 129 +/- 1 mm Hg, respectively). Sodium restriction did not reverse hypertension (190 +/- 8 mm Hg), but led to a significant reduction of relative heart weight compared to rats on the normal diet (2.94 +/- 0.24 vs. 3.86 +/- 0.23 mg/g, respectively; P less than 0.01). The hypertrophied hearts of animals on the regular diet showed depressed tissue catecholamines (significant only for norepinephrine); sodium restriction resulted in a restoration to normal levels. Thus, we demonstrated a dissociation of blood pressure and cardiac hypertrophy in the two-kidney one-clip model, similar to previous findings in other models. Our results support the concept that factors other than blood pressure contribute to cardiac hypertrophy. Dietary sodium intake appears to be one such factor. In addition, a possible role of the sympathetic nervous system is suggested.
The effects of human atrial 28-amino acid peptide on systemic and renal hemodynamics in anesthetized rats.
Authors: Hirata Y , Ishii M , Sugimoto T , Matsuoka H , Sugimoto T , Kangawa K , Matsuo H
Published: June 2012

The effects of synthetic human atrial 28-amino acid peptide (alpha-human atrial polypeptide) on systemic and renal hemodynamics were examined in two separate groups of Inactin-anesthetized rats. First, mean arterial pressure, heart rate, and cardiac output were measured before and during infusion of the peptide at rates of 0.04-0.67 microgram/kg per min. Cardiac output was determined by the dye-dilution method with a microcuvette inserted into a carotid-femoral arterial shunt. After 10 minutes of infusion, mean arterial pressure, cardiac output, and total peripheral resistance were reduced in a dose-dependent manner by 21% (P less than 0.001), 9% (P less than 0.05), and 11% (P less than 0.05), respectively, with 0.67 microgram/kg per min of alpha-human atrial natriuretic polypeptide. Despite the marked fall in blood pressure, the heart rate did not change. Second, urine volume, urinary sodium excretion, glomerular filtration rate ([3H]inulin clearance) and renal blood flow ([14C]p-aminohippuric acid sodium clearance and hematocrit) were measured. Increases in urine volume, urinary sodium excretion, filtration fraction, and fractional sodium excretion and a decrease in renal vascular resistance were dose dependent: +490% (P less than 0.01), +1340% (P less than 0.01), +19% (P less than 0.05), +1160% (P less than 0.01), and -18% (P less than 0.05), respectively, with 0.67 microgram/kg per min of alpha-human atrial natriuretic polypeptide. The glomerular filtration rate increased with 0.33 and 0.67 microgram/kg per min of alpha-human atrial natriuretic polypeptide (both P less than 0.05), whereas renal blood flow did not change.(ABSTRACT TRUNCATED AT 250 WORDS)
Early differentiation of infarcted and noninfarcted reperfused myocardium in dogs by quantitative analysis of regional myocardial echo amplitudes.
Authors: Haendchen R V , Ong K , Fishbein M C , Zwehl W , Meerbaum S , Corday E
Published: June 2012

This study tests the hypothesis that ischemic but viable reperfused myocardium can be differentiated from infarcted reperfused myocardium by regional analysis of myocardial echo amplitudes. In eight closed-chest, anesthetized dogs, the left anterior descending coronary artery was occluded for 3 hours, followed by 1 hour of reperfusion, and sacrifice. Infarct size was measured by the triphenyl tetrazolium chloride technique in a 1-cm-thick mid-left ventricular transverse slice, and matched with a corresponding end-diastolic two-dimensional echo short-axis cross-section. Outlining of epi- and endocardial surfaces, along with construction of a mid-myocardial outline, allowed measurements of regional myocardial echo intensities and grey-level histograms in subendo- and subepicardial regions. In 36 eventually infarcted subendocardial segments (greater than 20% wall necrosis), average pixel intensity (arbitrary units) was 73.7 +/- 33.1 (SD) in control, 75.8 +/- 33.0 at 3 hours of occlusion, and 107.8 +/- 40.9 at 5 minutes, 105.5 +/- 38.9 at 15 minutes, and 101.1 +/- 37.6 at 60 minutes postreperfusion P less than 0.05 vs. control or occlusion); intensity in normal segments (no or less than 20% wall necrosis) was 60.0 +/- 18.6 in control, 57.4 +/- 20.3 at 3 hours of occlusion, and 63.5 +/- 14.8, 68.0 +/- 27.9, and 64.2 +/- 22.3 at 5, 15, and 60 minutes postreperfusion, respectively (no significant change). The skew of the grey-level distribution in infarcted subendocardial segments did not change from control (0.49 +/- 0.72) to 3 hours of occlusion (0.41 +/- 0.52), but decreased (shift to higher echo amplitude) significantly at 5 minutes (-0.31 +/- 0.53), 15 minutes (-0.22 +/- 0.50), and 60 minutes (-0.28 +/- 0.45) after reperfusion (P less than 0.05 vs. control or occlusion); in normal subendocardial segments, there was no significant change throughout the study. In 31 partly infarcted subepicardial segments (greater than 50% wall necrosis), changes in postreperfusion echo amplitudes were less significant. Average pixel intensity was 71.3 +/- 28.6 in control, 71.8 +/- 29.2 after coronary occlusion, and 89.2 +/- 35.3, 83.7 +/- 37.5, and 85.6 +/- 34.9 at 5, 15, and 60 minutes after reperfusion, respectively. It is concluded that reperfusion of irreversibly injured myocardium is associated with consistent early increase in regional myocardial echo intensities and changes in the grey-level distribution. Such alterations might be used to detect the extent of tissue necrosis within minutes after reperfusion.
Impaired cardiopulmonary baroreflex control of renal nerves in renal hypertension.
Authors: Thames M D , Johnson L N
Published: June 2012

We recently reported that arterial baroreflex control of renal nerve traffic is impaired in renal hypertensive rabbits. The purpose of this study was to determine if vagal cardiopulmonary baroreflex control of renal nerve traffic is also impaired. Experiments were performed in 10 hypertensive (mean arterial pressure +/- SE in conscious state, 110 +/- 3 mm Hg) and 10 normotensive (79 +/- 1 mm Hg) chloralose-anesthetized rabbits. Responses to graded blood volume expansion (+5, +10, +15 ml/kg) with dextran in saline were recorded with all baroreflexes intact, after sinoaortic baroreceptor denervation, and after vagotomy. With arterial and cardiopulmonary baroreflexes intact, volume expansion resulted in decreases in renal nerve traffic of -12 +/- 2%/mm Hg increase in left atrial pressure in normotensive rabbits, but of only -5 +/- 2%/mm Hg in the hypertensive rabbits (P less than 0.05). This difference is particularly striking in view of the larger maximum increases in arterial (25 +/- 7 vs. 12 +/- 3 mm Hg) and left atrial pressure (9 +/- 1 vs. 6 +/- 1 mm Hg) during volume expansion in hypertensive vs. normotensive rabbits. After sinoaortic baroreceptor denervation, the responses of normotensive rabbits were preserved (-11 +/- 3%/mm Hg), while those of hypertensive rabbits were impaired further (-2 +/- 1%/mm Hg). Vagotomy abolished responses of renal nerves to volume expansion in both groups. These data demonstrate striking impairment of vagal cardiopulmonary baroreflex control of renal nerve traffic in renal hypertension. Even though arterial baroreflexes have been shown to be abnormal in renal hypertension, they still may partially compensate for markedly impaired cardiopulmonary baroreflex control of the renal nerves.
Pertussis toxin treatment blocks hyperpolarization by muscarinic agonists in chick atrium.
Authors: Sorota S , Tsuji Y , Tajima T , Pappano A J
Published: June 2012

Atrial and ventricular adenylate cyclase activity and atrial membrane potentials were measured in hearts from hatched chicks at 2-3 days after intravenous administration of pertussis toxin (0.5-1.0 micrograms, total) or saline. Both in atrium and ventricle, treatment with pertussis toxin antagonized inhibition by carbachol of basal and isoproterenol-stimulated adenylate cyclase activity without changing either basal or isoproterenol-stimulated adenylate cyclase. In atria from pertussis toxin-treated animals (5.4 mM potassium), carbachol hyperpolarized the resting membrane by 0.3 +/- 0.3 mV (n = 9) and did not increase resting potassium conductance. In contrast, carbachol hyperpolarized the resting membrane by 4.5 +/- 0.8 mV (n = 11) and increased resting potassium conductance more than 4-fold in saline-treated animals. Carbachol did not significantly affect the atrial action potential peak or duration at 50% repolarization of pertussis toxin-treated animals. This muscarinic agonist reduced action potential peak by 7.8 +/- 1.2 mV and the duration at 50% repolarization by 22.1 +/- 3.0 msec in atria from saline-treated animals. Pertussis toxin treatment also prevented the negative inotropic effect and the inhibition of calcium-dependent action potentials caused by carbachol in atrial muscle. Neither the affinity nor the maximal specific binding of [3H]quinuclidinyl benzilate in ventricular homogenates was changed by pertussis toxin treatment. The apparent affinity of carbachol for muscarinic receptor was slightly (approximately 2-fold) diminished in pertussis toxin-treated animals. The inhibition of carbachol-induced hyperpolarization by pertussis toxin treatment implicates a guanosine 5'-triphosphate-dependent protein (Ni or a similar protein) as an essential link that permits muscarinic receptor to regulate atrial potassium channels.
Effects of hemorrhage on renal nerve activity in conscious dogs.
Authors: Morita H , Vatner S F
Published: June 2012

We studied the effects of slow continuous hemorrhage (0.5 ml/kg per min) on measurements of arterial and left atrial pressures, and renal nerve activity in conscious dogs with all reflexes intact, or after sinoaortic baroreceptor denervation, cardiac denervation, or sinoaortic baroreceptor denervation plus vagal denervation. In intact dogs, mean arterial pressure remained relatively constant at 101 +/- 4 mm Hg until 20 +/- 4 ml/kg of hemorrhage, when renal nerve activity increased by 211 +/- 53%. At 39 +/- 2 ml/kg hemorrhage, mean arterial pressure fell by 48 +/- 3 mm Hg, and renal nerve activity returned to the prehemorrhage control level. Cardiac denervation did not affect the response of mean arterial pressure to hemorrhage, whereas, after sinoaortic baroreceptor denervation and sinoaortic baroreceptor plus vagal denervation, mean arterial pressure remained at its control level only through 8 +/- 1 and 4 +/- 1 ml/kg hemorrhage, respectively. The increases in renal nerve activity during nonhypotensive hemorrhage were significantly attenuated by either sinoaortic baroreceptor or cardiac denervation, and were completely blocked by sinoaortic baroreceptor plus vagal denervation. However, the decline in renal nerve activity with hypotensive hemorrhage was not blocked by either cardiac or sinoaortic baroreceptor denervation, and was enhanced after sinoaortic baroreceptor plus vagal denervation. Our data indicate that nonhypotensive hemorrhage in the conscious dog elicits a striking increase in renal nerve activity, which then returns to control levels during hypotensive hemorrhage. Both sinoaortic and cardiopulmonary baroreceptors are involved in mediating the increase in renal nerve activity, whereas the decline in renal nerve activity is not due to either of these baroreflexes.
Altered calcium handling in experimental pressure-overload hypertrophy in the ferret.
Authors: Gwathmey J K , Morgan J P
Published: June 2012

The purpose of this study was to evaluate the relationship between changes in the intracellular handling of free, ionized calcium and the functional alterations that occur in cardiac hypertrophy. We developed a model of right ventricular pressure-overload hypertrophy in the ferret by critical banding of the pulmonary artery; this method produced significant degrees of hypertrophy within 1-3 months of surgery. We removed papillary muscles, 1 mm or less in diameter, from ferrets with cardiac hypertrophy and their age- and weight-matched controls, and loaded them with the bioluminescent calcium indicator, aequorin, in order to record intracellular calcium transients. Compared to the controls, the hypertrophied muscles demonstrated a prolonged duration of isometric contraction but a marked decrease in peak isometric tension development. The increased duration of isometric contraction in the hypertrophied muscles correlated with a similar prolongation of the calcium transient; we interpret this to mean that the rate of sequestration and perhaps release of calcium by intracellular stores is decreased in hypertrophy. In contrast, the amplitudes of the calcium transients were similar in muscles from both groups of ferrets, indicating that the diminution in peak tension developed by the hypertrophied muscles was not due to decreased availability of activator calcium. We conclude that the prolonged time course of tension development, but not the diminished peak isometric tension response, may be related to changes in intracellular calcium handling.
Frequency, amplitude, and propagation velocity of spontaneous Ca++-dependent contractile waves in intact adult rat cardiac muscle and isolated myocytes.
Authors: Kort A A , Capogrossi M C , Lakatta E G
Published: June 2012

Spontaneous contractile waves due to spontaneous calcium cycling by the sarcoplasmic reticulum occur in unstimulated bulk rat papillary muscle and single rat cardiac myocytes with intact sarcolemmal function. We used video analytic techniques to quantify the wave characteristics in both bulk muscle and myocytes; laser-light scattering techniques were also employed in muscle. In muscle bathed in physiological concentrations of calcium, the true periodicity of these waves was a fraction of 1 Hz and increased up to several hertz with increases in cell calcium. This was paralleled by an increase in the frequency of scattered laser light intensity fluctuations. In myocytes, a range of spontaneous contractile wave frequencies similar to that which occurred in the muscle was observed; it could be demonstrated that an increase in superfusate calcium concentrations (2-15 mM at 23 degrees C) increases the oscillation frequency but not amplitude. In both myocytes and muscle, low concentrations of caffeine (0.5 mM) and higher temperature increased the oscillation frequency but diminished their amplitude. However, the scattered light fluctuations did not change with temperature and decreased with caffeine. These results demonstrate that (1) the true frequency of spontaneous sarcoplasmic reticulum oscillations in the unstimulated rat muscle and single myocytes with intact sarcolemmal function is low, i.e., a fraction of a hertz; (2) with cell calcium loading, the oscillation frequency accelerates to those frequencies measured previously in the "calcium overload" state; (3) while scattered light fluctuations which sample myofilament motion are a sensitive, noninvasive method of detecting the oscillations in bulk muscle, they can be insensitive to the divergent changes in oscillation amplitude and frequency.
Calcium-dependent enhancement of myocardial diastolic tone and energy utilization dissociates systolic work and oxygen consumption during low sodium perfusion.
Authors: Renlund D G , Lakatta E G , Mellits E D , Gerstenblith G
Published: June 2012

The relationships and correlations among functional, metabolic, and ionic consequences of low sodium perfusion were studied in isovolumic, retrograde-aortic perfused working rat hearts by 31P nuclear magnetic resonance, oxygen consumption, and atomic absorption spectrometry. Reduction of perfusate sodium from 144 to 74, 51, 39, and 25 mM in four separate groups of hearts via lithium substitution for 15 minutes decreased cell sodium to mean values of 62, 51, 43, and 36 mumol/g dry weight, respectively (P less than 0.001 vs. control of 107). There was a transient rise and then a fall in developed pressure and a decline in phosphocreatine and adenosine triphosphate, all of which were graded and correlated with perfusate sodium (P less than 0.01 for all parameters vs. perfusate sodium). This was accompanied by a 2- to 7-fold elevation of diastolic pressure while oxygen consumption remained near control levels. All parameters except adenosine triphosphate returned toward baseline values when normal perfusate sodium was reintroduced. Although cell calcium as measured by atomic absorption spectrometry did not differ among the groups, the functional and metabolic changes did not occur if the sodium steps were performed in reduced perfusate calcium (0.08 mM). In hearts in which systolic function was obliterated by verapamil, exposure to zero sodium caused a 4-fold increase in oxygen consumption, an increase in diastolic pressure, and a reduction of high energy phosphates. In the presence of ryanodine, a specific inhibitor of sarcoplasmic reticulum calcium release, the metabolic changes did not occur, and the excess oxygen consumption in zero sodium was substantially reduced. Thus, the effect of lowered perfusate sodium in beating hearts, i.e., to dissociate oxygen consumption and systolic function, and to increase diastolic pressure and its effect in arrested hearts to increase oxygen consumption, are calcium dependent, energy consuming, and modulated by sarcoplasmic reticulum calcium cycling.
Age-related changes in ploidy levels and biochemical parameters in cardiac myocytes isolated from spontaneously hypertensive rats.
Authors: Engelmann G L , Vitullo J C , Gerrity R G
Published: June 2012

Postnatal growth of the mammalian ventricular myocyte is characterized by a brief period of hyperplasia followed by an extensive period of physiological hypertrophy. Using myocytes isolated from both Wistar-Kyoto and spontaneously hypertensive rats from fetus to 10 months old, we analyzed morphological, biochemical, and ploidy changes. Fetal myocytes from both spontaneously hypertensive and Wistar-Kyoto rats were mononuclear, diploid cells. By 4 weeks, adult binucleation levels (84% binuclear) were found, and myocytes pooled from both ventricles demonstrated nuclear ploidy shifts to tetraploid levels. However, analysis of myocytes isolated from left ventricle, right ventricle, and septum showed that nuclear polyploidation was confined to the right ventricle and septum, with few polyploid nuclei detected in the left ventricle. This pattern remained relatively constant through 10 months of age, although spontaneously hypertensive myocytes showed significantly more polyploidation than Wistar-Kyoto in all regions. Biochemical analysis of isolated myocytes substantiated the nuclear ploidy changes and demonstrated elevated protein and ribonucleic acid content in left ventricular myocytes without extensive polyploidation. Since cardiac hypertrophy, both physiological and pathological, is associated primarily with the left ventricle and occurs in the absence of significant ploidy changes, these findings suggest that a unique pattern of gene regulation may be ongoing in the left ventricle myocytes that is not present in the septum and right ventricle. These variations may be essential for cellular hypertrophy under normal and pathological conditions.
The control of sugar uptake by metabolic demand in isolated adult rat heart cells.
Authors: Haworth R A , Berkoff H A
Published: June 2012

To investigate the control of sugar uptake by metabolic demand, we used isolated quiescent adult rat heart cells in suspension, under conditions similar to those found during anoxia. Metabolic demand was varied by exposing cells to rotenone plus various levels of p-trifluoromethoxyphenylhydrazone. Without glucose, the time taken for half of the cells to undergo contracture was inversely proportional to the metabolic demand as measured by the rate of lactate production. For any metabolic demand, the onset of contracture was preceded by a sudden drop in adenosine triphosphate. The permeability of contracted cells to glucose was investigated using 3-O-methylglucose. The rate of 3-O-methylglucose uptake by such cells was strongly dependent on the time taken for half the cells to undergo contracture, with low rates at low times to half contracture, and insulin-like rates at high times to half contracture. This suggests that the full induction of glucose transport by metabolic demand can be prematurely curtailed by the loss of adenosine triphosphate. This phenomenon appeared to limit glucose utilization in cells with a high metabolic demand when glucose was present: such cells underwent contracture unless insulin was also present, the rate of glucose uptake as measured with 2-deoxyglucose was inhibited, and the rate of lactate production was inhibited. Isoproterenol depressed glucose transport by two mechanisms. First, by stimulating the basal metabolic demand of the cell it reduced the time taken for half the cells to undergo contracture and, hence, the level of induced sugar transport. Second, it significantly delayed the onset of sugar permeability with respect to the contracture event.(ABSTRACT TRUNCATED AT 250 WORDS)
Hypothalamic beta 2-adrenoceptor control of renal sympathetic nerve activity and urinary sodium excretion in conscious, spontaneously hypertensive rats.
Authors: Koepke J P , Jones S , DiBona G F
Published: June 2012

The contributions of beta 1-, B2-, and alpha 2-adrenoceptors in the posterior hypothalamus to the increased renal sympathetic nerve activity and decreased urinary sodium excretion resulting from environmental stress (air jet) in conscious spontaneously hypertensive rats were examined. Air stress increased mean arterial pressure and renal sympathetic nerve activity (54% from 7.0 +/- 0.7 integrator resets/min), and decreased urinary sodium excretion (44% from 2.7 +/- 0.4 microEq/min per 100 g body weight). After bilateral injection of ICI 118,551 (beta 2-adrenoceptor antagonist) into the posterior hypothalamus of the same spontaneously hypertensive rats, air stress had no effect on renal sympathetic nerve activity (8% from 4.8 +/- 0.7 integrator resets/min) or urinary sodium excretion (2% from 5.2 +/- 0.8 microEq/min per 100 g body weight), but still increased mean arterial pressure. Bilateral injection of isoproterenolol (beta-adrenoceptor agonist) into the posterior hypothalamus enhanced the renal sympathetic nerve activity and urinary sodium excretion (but not mean arterial pressure) responses to air stress. Air stress had no effect on renal sympathetic nerve activity or urinary sodium excretion when ICI 118,551 was given into the posterior hypothalamus before isoproterenol. Atenolol (beta 1-adrenoceptor antagonist) had no effect on the renal responses to air stress when given alone or before isoproterenol. Similarly, ICI 118,551 administered into the lateral hypothalamus or lateral cerebral ventricle, or guanabenz (alpha 2-adrenoceptor agonist) given into the posterior hypothalamus, had no effects on the renal or mean arterial pressure responses to air stress. Thus, beta 2-adrenoceptors in the posterior hypothalamus mediate the increased renal sympathetic nerve activity and antinatriuresis resulting from environmental stress in conscious spontaneous hypertensive rats.
Reconstruction of propagated electrical activity with a two-dimensional model of anisotropic heart muscle.
Authors: Roberge F A , Vinet A , Victorri B
Published: June 2012

The propagated electrical activity in normal anisotropic cardiac muscle is characterized by directionally dependent variations in the rising phase of the action potential. An important question concerns the relation between such variations and the propagation velocity and extracellular potentials. This problem was studied here in a sheet of cells, under conditions of uniform intracellular anisotropic resistivity and constant electrical membrane properties, through a numerical solution of the two-dimensional propagation equation. The numerical solution implies a lumping of the cytoplasmic and intercellular resistances into an equivalent junctional resistance to form a distributed resistive network representing the intracellular domain. The interstitial space is assumed isotropic and unbounded, with a resistivity of 100 omega X cm. The electrical properties of the cell membrane are represented by a Beeler-Reuter model. The stimulus current is applied to a small area of the sheet, and attention is focussed on the stable propagated events occurring some 5 or 6 length constants away from the stimulation site. The numerical solution is a good approximation of a continuous uniform structure when the cell size is less than 10% of the length constant along both major axes. Conditions of non-uniform propagation, with directionally dependent variations in the maximum rate of rise and time constant of the foot of the action potential were simulated by increasing the cell size to 30% of the length constant in the transverse direction of the sheet. Our results indicate that the directional changes in the maximum rate of rise correspond to small modifications of the extracellular potentials, while the directional changes in time constant of the foot are associated with the propagation velocity. The maximum effects are observed along the transverse direction as follows: a 19% increase in maximum rate of rise corresponds to a decrease of about 6% in the peak-to-peak amplitude of the extracellular potential, and a 24% increase in time constant of the foot is associated with a decrease of about 7% in the propagation velocity. Under the conditions of the present study, however, the simulated directional changes in maximum rate of rise are smaller than those experimentally observed so the corresponding changes in the extracellular potentials are probably underestimated.
A phosphorus-31 nuclear magnetic resonance study of the metabolic, contractile, and ionic consequences of induced calcium alterations in the isovolumic rat heart.
Authors: Hoerter J A , Miceli M V , Renlund D G , Jacobus W E , Gerstenblith G , Lakatta E G
Published: June 2012

Isolated adult rat hearts perfused in an isovolumic mode were used to study the effects of sodium-potassium pump inhibition and sodium-calcium exchange alterations on the tissue content of adenosine triphosphate, phosphocreatine, inorganic phosphate, and intracellular pH, all measured by phosphorus-31 nuclear magnetic resonance spectroscopy. Rates of oxygen consumption, contractile function, and the cell contents of calcium, sodium, and potassium also were determined. The inhibition of sodium-potassium adenosine triphosphatase, either by the reduction in perfusate potassium from 5.9 to 1 millimolar or less, or by the addition of 10(-4) molar ouabain, transiently increased systolic pressure. This was followed by a decrease in systolic pressure, an increase in diastolic pressure, and eventual inexcitability. This contractile profile was accompanied by a persistent increase in oxygen consumption, a monotonic decline in cellular adenosine triphosphate and phosphocreatine content, the development of marked intracellular acidosis, a gain in cell sodium and calcium content, and a reduction in cell potassium. Quite similar metabolic changes were also observed when cell calcium was increased after a reduction in perfusate sodium. These metabolic and contractile effects could be prevented or reversed by decreasing perfusate calcium. The results emphasize the profound role of calcium in modulating cell oxygen consumption, energy balance, pH, excitability, and force production. These data are discussed in light of changes in the myocardial energy supply/demand balance, as well as from the viewpoint of the known competition between mechanisms for mitochondrial calcium transport vs. high-energy phosphate production.
The distribution of functional impairment across the lateral border of acutely ischemic myocardium.
Authors: Gallagher K P , Gerren R A , Stirling M C , Choy M , Dysko R C , McManimon S P , Dunham W R
Published: June 2012

To evaluate the degree and lateral extent of dysfunction in nonischemic myocardium adjacent to ischemic muscle, we measured systolic wall thickening with sonomicrometers during circumflex coronary occlusion in 12 anesthetized, open-chest dogs. The locations of the wall thickness measurements relative to the perfusion boundary were determined with myocardial blood flow (microspheres) maps constructed from multiple, small tissue samples. Five minutes after circumflex occlusion, systolic wall thickening in the central ischemic zone decreased from 3.00 +/- 0.61 (mean +/- SD) mm to -0.61 +/- 0.36 mm (P less than 0.01). In nonischemic myocardium greater than 10 mm from the perfusion boundary, systolic wall thickening increased from 2.56 +/- 0.57 to 3.24 +/- 0.72 mm (P less than 0.01). In nonischemic myocardium within 10 mm of the perfusion boundary, systolic wall thickening was slightly but significantly reduced compared with control (2.72 +/- 0.80 to 2.44 +/- 0.79 mm, P less than 0.05), supporting the concept of regional dysfunction in nonischemic myocardium at the lateral borders of an ischemic area. Sigmoid curves were fitted to the data to model changes in wall thickening as a continuous function of distance from the perfusion boundary. This allowed estimation of the extent of dysfunction into nonischemic myocardium which averaged less than 8 mm (approximately 30 degrees of endocardial circumference) at one border. The level of functional impairment in this zone was relatively modest, and systolic wall thickening in the immediate border area was reduced more than 50% from control only in tissue characterized by a blood supply of mixed ischemic and nonischemic origin. We conclude that a functional border zone exists lateral to an acutely ischemic area, but measurement of regional function produces relatively small exaggeration of the size of the acutely ischemic zone if severe reduction in mechanical performance is used to define the extent of the ischemic area.
A different cleavage site for high molecular weight kininogen in vivo following intravenous injection of dextran sulfate in the rabbit.
Authors: Wiggins R C
Published: June 2012

Purified radiolabeled rabbit Hageman factor, prekallikrein, and high molecular weight kininogen were used to examine Hageman factor system molecular dynamics after the intravenous injection of heparin-like dextran sulfate polymer in the rabbit. Hageman factor system proteins rapidly disappeared from the circulation following dextran sulfate injection, as measured by radial immunodiffusion, by kaolin-releasable kinin formation, and by measuring circulating levels of radiolabeled Hageman factor, prekallikrein, and high molecular weight kininogen. 125I-Hageman factor was distributed mainly to lung, liver, and spleen following dextran sulfate injection. Proteolysis of circulating 125I-Hageman factor occurred at a site within a disulfide loop into fragments of 50,000 and 30,000 molecular weight. Proteolysis of 125I-prekallikrein also occurred with visualization of a 50,000 molecular weight fragment. Although extensive proteolysis of 131I-high molecular weight kininogen was observed, the cleavage fragments were not the same as those generated during contact activation in vitro. The major fragment of high molecular weight kininogen observed in vivo was at 80,000 molecular weight, in contrast to the 65,000 molecular weight fragment generated by kallikrein in vitro. These results indicate that high molecular weight kininogen can undergo proteolysis in vivo into fragments not known to be associated with kinin release.
Regional comparison of midwall segment and area shortening in the canine left ventricle.
Authors: Lew W Y , LeWinter M M
Published: June 2012

We used ultrasonic segment length gauges to examine the regional behavior of midwall fibers at different sites around the left ventricular minor axis in 12 anesthetized dogs. In six dogs (group I) with circumferentially oriented midwall gauges, significantly greater shortening of anterior than lateral or posterior wall segments was demonstrated over a range of left ventricular end-diastolic pressures from 2 to 18 mm Hg. Normalized end-diastolic segment lengths increased more in the anterior wall as end-diastolic pressure increased, suggesting that regional differences in diastolic distensibility may in part account for the observed shortening differences. To examine the extent to which shortening of longitudinally oriented fibers of the subendocardium and subepicardium might influence the behavior of the midwall circumferential fibers, we implanted mutually perpendicular midwall gauges circumferentially and longitudinally in the anterior and posterior walls in six dogs (group II). Longitudinal shortening of midwall fibers was negligible at low end-diastolic pressures, but increased significantly at higher end-diastolic pressures. In the anterior wall, there was greater circumferential than longitudinal shortening, whereas, in the posterior wall, shortening was similar in the two directions. Finally, we calculated the midwall area subtended by the mutually perpendicular gauges and found the systolic change in midwall area to be similar for the anterior and posterior walls at all end-diastolic pressures. We conclude that midwall fibers demonstrate considerable nonuniformity of contraction at different sites around the minor axis. This finding may be related in part to regional differences in diastolic distensibility or in functional interactions between fiber layers. Despite these complex regional, directional, and volume dependent differences in midwall segment function, the systolic changes in midwall area did not vary regionally. Thus, different midwall sites around the minor axis circumference appear to have similar overall contributions to the ejection of blood.