Middle-age abolishes cardioprotection conferred by thioredoxin-1 in mice

Thioredoxin-1 (Trx1) has cardioprotective effects on ischemia/reperfusion (I/R) injury, although its role in ischemic postconditioning (PostC) in middle-aged mice is not understood. This study aimed to evaluate if combining two cardioprotective strategies, such as Trx1 overexpression and PostC, could exert a synergistic effect in reducing infarct size in middle-aged mice. Young or middle-aged wild-type mice (Wt), transgenic mice overexpressing Trx1, and dominant negative (DN-Trx1) mutant of Trx1 mice were used. Mice hearts were subjected to I/R or PostC protocol. Infarct size, hydrogen peroxide (H2O2) production, protein nitration, Trx1 activity, mitochondrial function, and Trx1, pAkt and pGSK3β expression were measured. PostC could not reduce infarct size even in the presence of Trx1 overexpression in middle-aged mice. This finding was accompanied by a lack of Akt and GSK3β phosphorylation, and Trx1 expression (in Wt group). Trx1 activity was diminished and H2O2 production and protein nitration were increased in middle-age. The respiratory control rate dropped after I/R in Wt-Young and PostC restored this value, but not in middle-aged groups. Our results showed that Trx1 plays a key role in the PostC protection mechanism in young but not middle-aged mice, even in the presence of Trx1 overexpression.

Relation between periodontal disease and arterial stiffness

BACKGROUND AND OBJECTIVE

Periodontal disease has been described as playing a role in the atherosclerosis process, and its relation with intimal thickness and vascular endothelial function (EF) has been investigated. The present study sought to determine whether there are differences in parameters of arterial stiffness and EF between patients with and without severe periodontal disease (SPD).

MATERIAL AND METHODS

Patients referred to the School of Dentistry University of Buenos Aires, were assessed. Demographic characteristics, atherogenic risk factors and concomitant pathologies were recorded. Patients with known cardiovascular pathology were excluded. Using carotid Doppler ultrasound an operator assessed arterial stiffness parameters: compliance, elastic modulus (EM), β stiffness index (βSI) and vascular EF by brachial artery flow-mediated dilatation. The patients were divided into two groups: with and without SPD.

RESULTS

Forty patients were included; 60% were women; 15 were in the SPD group and 25 in the group without SPD. Respective results of the studied variables were: age 56.53 ± 17.58 vs. 51.12 ± 12.97 years (NS); probing depth 2.53 ± 1.30 (95% CI 1.81-3.25) vs. 1.25 ± 0.51 (95% CI 1.31-1.73) p = 0.02; clinical attachment level 4.80 ± 2.00 (95% CI 3.69-5.91) vs. 1.72 ± 0.93 (95% CI 1.33-2.11) p = 0.001; intimal thickness 0.10 ± 0.17 (95% CI 0.095-0.11) vs. 0.82 ± 0.18 (95% CI 0.074-0.98) (NS); EM 48.33 ± 12.53 vs. 38.86 ± 7.69 (p = 0.005); βSI 4.21 ± 1.03 vs. 3.64 ± 1.02 (p = 0.004); EF 16.13 ± 5.02 vs. 22.76 ± 4.50 (p = 0.0003). Correlation between: EM and clinical attachment level r = 0.58 (p < 0.001), βSI and clinical attachment level r = 0.66 (p < 0.001), EF and clinical attachment level 0.59 (p < 0.001).

CONCLUSIONS

Parameters of arterial stiffness and EF were worse in patients with SPD and correlated moderately with clinical attachment level. Correlation with compliance and EF was negative.

Impaired cardiac mitochondrial function and contractile reserve following an acute exposure to environmental particulate matter

BACKGROUND

It has been suggested that mitochondrial function plays a central role in cardiovascular diseases associated with particulate matter inhalation. The aim of this study was to evaluate this hypothesis, with focus on cardiac O2 and energetic metabolism, and its impact over cardiac contractility.

METHODS

Swiss mice were intranasally instilled with either residual oil fly ash (ROFA) (1.0 mg/kg body weight) or saline solution. After 1, 3 or 5 h of exposure, O2 consumption was evaluated in heart tissue samples. Mitochondrial respiration, respiratory chain complexes activity, membrane potential and ATP content and production rate were assessed in isolated mitochondria. Cardiac contractile reserve was evaluated according to the Langendorff technique.

RESULTS

Three hours after ROFA exposure, tissue O2 consumption was significantly decreased by 35% (from 1180 +/- 70 to 760 +/- 60 ng-at O/min g tissue), as well as mitochondrial rest (state 4) and active (state 3) respiration, by 30 and 24%, respectively (control state 4: 88 +/- 5 ng-at O/min mg protein; state 3: 240 +/- 20 ng-at O/min mg protein). These findings were associated with decreased complex II activity, mitochondrial depolarization and deficient ATP production. Even though basal contractility was not modified (control: 75 +/- 5 mm Hg), isolated perfused hearts failed to properly respond to isoproterenol in ROFA-exposed mice. Tissue O2 consumption rates positively correlated with cardiac contractile state in controls (r2 = 0.8271), but not in treated mice (r2 = 0.1396).

GENERAL SIGNIFICANCE

The present results show an impaired mitochondrial function associated with deficient cardiac contractility, which could represent an early cardiovascular alteration after the exposure to environmental particulate matter.

Doctor-patient sexual relationships in medical oaths

BACKGROUND

Doctor-patient sexual relationship is considered to be unfair because the first party would be abusing the second party's vulnerability. The prohibition of this relationship is noted in the Hippocratic oath. Currently, a reprise of the use of oaths in medical schools can be observed.

AIM

To determine whether the prohibition has been maintained and how its expression has varied in the oaths during different periods.

METHODS

50 oaths were studied: 13 ancient-medieval and 37 modern-contemporary. Of the 50 texts, 19 were versions of the original oaths. The oaths that pointed out the prohibited doctor-patient relationship referred to any sexual aspect or included paragraphs that began as the Hippocratic oath does were noted.

RESULTS

Of the 24 (48%) texts that expressed the prohibition, 8 (62%) were ancient-medieval and 16 (43%) were modern-contemporary. Some expressly call it Hippocratic oath, many use general terminology (corruption or vice) and others describe it in association with other commitments (abortion and euthanasia).

CONCLUSIONS

The clause on the prohibition of the doctor-patient sexual relationship in Hippocratic oath was included to be for legal, economic and social reasons at the time. That the clause is found mostly in the ancient-medieval oaths can be attributed to the influence of the original. This commitment is generalised and associated with others by contemporary formulas. Currently, sexual relationships are the subject of legal and ethical analysis and their inclusion in the oaths is being debated.

[Time course of the myocardial infarction in the rabbit]

The histopathologic evolution of myocardial infarct and of areas distant from infarct in rabbit hearts was studied. The left coronary artery of 55 rabbits was ligated, and rabbits were sacrificed at 2, 4, 6, 8, 12, 14, 16, 18, 26, 35 and 56 days post-ligature (n = 5 per group). Two rabbits were used as control and two were sham operated. The hearts were excised, cut in slices and stained with hematoxilin-eosin, Masson's trichrome and picrosirius red. Histological evaluation was semi-quantitative (scale: 0 to +++). At day 2, presence of neutrophils was +++, disappearing completely at day 6. Fibroblast proliferation increased from day 4 to day 14 post-occlusion. Coagulation necrosis in medial myocardium during the first week was +++. Subendocardic myocytolysis was evident from day 2 up to day 56 post-infarction. During the second week, proliferation of lymphocytes and macrophages (+++), granulation tissue formation (+++), and incipient traces of fibrosis that peaked at day 35 were observed. Cicatrization was complete at day 56 (+++). In areas far from infarction (right ventricle and septum), proliferation of fibroblasts was observed at day 2, and perivascular, interstitial and endocardic fibrosis at day 16. In conclusion, myocardial infarction in rabbits, unlike myocardial infarction in human beings, is characterized by early presence of fibroblasts and subendocardic fibrosis, and quick increase and precocious disappearance of neutrophils. An interesting finding was the early proliferation of fibroblasts in normal areas far from infarct.

[The activation of A1 adenosine receptors attenuates myocardial stunning in the rabbit]

Hearts exposed to a prolonged period of ischemia (> or = 30 minutes) present smaller infarct size when reperfused in the presence of adenosine. However, when the period of ischemia is shorter, the infarct areas are not very significant, but a postischemic ventricular dysfunction persists. The objective of this study was to determine the effect of adenosine, (administered only during reperfusion) on systolic and diastolic alterations present in postischemic ventricular dysfunction, as well as to determine whether A1 receptors participate in this effect. Isolated isovolumic rabbit hearts were subjected to 15 minutes of global ischemia followed by 30 minutes of reperfusion. Before ischemia and during reperfusion ventricular function was evaluated. In the control group, the left ventricular developed pressure (LVDP) reached 56 +/- 2% of recovery at 30 minutes of reperfusion. The administration of adenosine improved LVDP 75 +/- 3% (P < 0.05 vs. control). However, when adenosine was given in presence of an A1 receptor selective antagonist (DPCPX), LVDP reached 50 +/- 2% (P < 0.05 vs. control). In the control group, left ventricular end diastolic pressure (LVEDP) (diastolic stiffness), increased 293 +/- 4%, at 30 minutes of reperfusion. Only a 15 +/- 8% (P < 0.05 vs. control) increase in LVEDP was observed with adenosine. Reperfusion with adenosine plus DPCPX did not attenuate an increase of 493 +/- 9% (P < 0.05 vs. control) in diastolic stiffness. Adenosine administered from the beginning of reperfusion attenuated both systolic alterations and diastolic stiffness in postischemic dysfunction. This effect was abolished by DPCPX, suggesting an important role for the A1 receptors in adenosine protection.

[Confidentiality in medical oaths: (When the white crow becomes gray...)]

Confidentiality, together with the ethical principles of beneficence and non-maleficence, is the most important rule in Medical Oaths at the present time. However, the scientific-technical advances in medicine have made this rule one of the most controversial ones because of its exceptions. In consequence, the aim of the present paper is to comparatively analyze the rule of confidentiality in Medical Oaths of different places, times, origins and in different versions of the Hippocratic Oath in order to determine what should be kept a secret and with what degree of commitment (absolute or "prima facie"). Of the thirty six analyzed Oaths, twenty-seven manifest this rule and nine do not. No relation was found between the manifestation of this rule and the place, time, origin and different versions of the Hippocratic Oath. Most pledges suggest not to reveal what has been seen or heard during the medical act, the same as in the Hippocratic Oath. Seven texts point out that confidentiality should be absolute and four give exceptions in connection with beneficence and justice principles and the moral duty of causing no damage to third parties. Two pledges specify protection of privacy. In conclusion, today confidentiality is considered to be a moral duty for the benefit of the patient and out of consideration for his autonomy; however, at the present time in medicine the duty of keeping absolute secrecy is being reconsidered.

[Exogenous adenosine and postischemic dysfunction in the isolated rabbit heart]

It is recognized that adenosine lessens the systolic alterations of the postischemic ventricular dysfunction ("stunned myocardium"), but little is known about the drug's effects on the diastolic phase of the cardiac cycle. The aim of this work was to determine the effect of adenosine when it was administered: a) before ischemia and during reperfusion, and b) from the early reperfusion period to the end of the experiment on the systolic and diastolic function of the "stunned myocardium". An additional objective was to determine whether adenosine modifies the release of creatine phosphokinase (CPK) and lactate dehydrogenase (LDH), in the "stunned myocardium". Rabbit isolated isovolumic hearts were perfused according to Langendorff's technique, and subjected to 15 minutes global ischemia and 30 minutes reperfusion. A small latex balloon was inserted into the left ventricle via the left atrium which allowed to measure the ventricular end-diastolic pressure (diastolic stiffness) and calculate the developed pressure, the maximal rate of pressure generation and maximal rate of pressure decay (+dP/dtmax and -dP/dtmax), the ratio between these two variables (+P/-P), and the time constant of isovolumic relaxation (tau, Tau). The adenosine administered both before the ischemia period, and at the beginning of reperfusion, attenuated the systolic and diastolic stiffness alterations without modifying the isovolumic relaxation. The administration of adenosine did not diminish the CPK and LDH release significantly when it was given before the ischemia period or the beginning of reperfusion.

[Analysis of the ethical principles of beneficence and no harm in medical oaths in relation with the Hippocratic one]

The principles of beneficence and no-maleficence, already set forth in the Hippocratic Oath, have been the foundation of medical ethics for the last twenty-five centuries. The principle of beneficence is currently maintained in most wordings of the pledges of medical schools of the United States, Canada and Argentina; it is not the same with the principle of non-maleficence. The aim of this paper is to determine whether these principles are described in medical oaths at different times. These principles did not remain in an oaths. Of twenty-nine analyzed texts, nine describe both principles simultaneously, eleven only mention beneficence; three only express non-maleficence, and six indicate neither of them. Most wordings that describe these principles are modifications of the Hippocratic Oath. Two contemporary wordings describe the achievement of the greatest benefit with minimum harm. Two current wording also subordinate the principle of beneficence to the principle of respect for the patient's autonomy, and eight wordings indicate not only patients' benefit in particular but that of society in general. It is not possible to ignore that it is no enough to fulfill only these two principles. Physicians should encourage the development of patients' responsibility in managing their own health and respect their autonomy.

Is stunning prevented by ischemic preconditioning?

In a model of global ischemia in the isolated perfused rat heart, a 20 min ischemic period followed by 30 min of reperfusion induces a decrease in isovolumic developed pressure (LVDP) and +dP/dtmax to 61+/-6% and 61+/-7% of baseline, respectively. Left ventricular end-diastolic pressure (LVEDP) increases to 36+/-4 mmHg at the end of the reperfusion period. No significant necrotic area as assessed by triphenyltetrazolium chloride (TTC) was detected at the end of the reperfusion period. By an immunohistochemical method using antiactin monoclonal antibodies 10.8+/-1.9% of unstained cells were detected in the stunned hearts and 10.3+/-1.2% in control hearts. Preceding the ischemic episode with a cycle of 5 min of ischemia followed by 10 min of reperfusion (ischemic preconditioning) protected contractile function. LVDP and +dP/dtmax now stabilized at 89+/-5% and 94+/-5% of baseline respectively. LVEDP was 20+/-2 mmHg at the end of the reperfusion period. The protection of contractile dysfunction after 20 min of ischemia was achieved also by early reperfusion of low Ca2+-low pH perfusate. With this intervention LVDP stabilized at 87+/-5% of baseline. LVEDP was 12+/-2 mmHg at the end of the reperfusion period. A positive inotropic intervention induced by a modified postextrasystolic potentiation protocol at the end of the reperfusion period increases LVDP to levels higher than baseline in the stunned hearts. However, these values were less than those obtained in control hearts. Ischemic preconditioning significantly increased the maximal inotropic response. Therefore, ischemic preconditioning diminishes the contractile dysfunction of early stunning.

Comparison of the effects of ACE inhibition with those of angiotensin II receptor antagonism on systolic and diastolic myocardial stunning in isolated rabbit heart

The aim was to determine whether enalaprilat (0.08 mg/kg/min) or losartan (0.01 mg/kg/min) administration before ischemia can improve postischemic systolic and diastolic dysfunction ('stunned myocardium') and attenuate the 'hyperfunction' phase at the beginning of reperfusion. An isolated isovolumic rabbit heart preparation was subjected to 15 min of ischemia followed by 30 min of reperfusion without (group 1) or with pretreatment with enalaprilat (group 2) or losartan (group 3). Left ventricular developed pressure and end-diastolic pressure (diastolic stiffness) were measured and the time constant of isovolumic relaxation (T, Tau) and the ratio between +dP/dt and -dP/dt were calculated. In comparison to the stunned group (group 1) both enalaprilat (group 2) and losartan (group 3) exerted a significant protective effect on postischemic recovery of contractile state and diastolic stiffness. Only enalaprilat attenuated the 'hypercontractile' phase. However, both enalaprilat and losartan failed to improve myocardial relaxation. In summary, these data strongly suggest a direct deleterious action of the local renin-angiotensin system on ischemic myocardium and diminution of myocardial stunning with its successful blockade. Although, we can not exclude the possibility that bradykinin has some cardioprotective effect, these data suggest that angiotensin exacerbates myocardial injury.

[Analysis of the ethical principles in medical oaths used by medical schools of Argentina in relation to the Hippocratic Oath]

Medical oaths have consulted the source of all Medical Ethics through centuries. Since the 60s a new consensus on ethics was sought to apply to the new medical problems. The consensus was on the basic principles: beneficence, non-maleficence, justice and respect for the patient's autonomy with its two rules of confidentiality and veracity. The Hippocratic Oath specifies the principles of beneficence and non-maleficence and the rule of confidentiality. They are included in the texts used in different Medical Schools of the United States, Canada and the United Kingdom. The purpose of this analysis is to determine which of those ethical principles are included in the Argentinian Medical Oaths. At present, out of the ten Faculties of Medicine that use a formula, six choose the Declaration of Geneva and the rest use their own texts. No schools use the Hippocratic Oath. Neither of the five different Oaths include the four principles. The rule of confidentiality is the one most frequently mentioned followed by the principles of beneficence and justice. The principles of non-maleficence and of respect for the patient's autonomy, in general, and the rule of veracity, in particular, are not indicated. Revision of the Medical Oaths used in Argentina, is basically for the ethical revision suggested, in order to include all the ethical principles strongly agreed upon.

[Effect of enalaprilat on postischemic systolic and diastolic dysfunction (stunned myocardium) on the isolated rabbit heart]

The aim was to determine: 1) whether Enalaprilat (0.08 mg/kg/min) administration: a) before ischemia or b) at the beginning of reperfusion improved the postischemic systolic and diastolic dysfunction ("stunned myocardium") and attenuated the "hyperfunction" phase at the beginning of reperfusion; and 2) whether creatine kinase (CPK), and lactate dehydrogenase (LDH) activities, and lactate release are involved in the protective effects of Enalaprilat. An isolated isovolumic rabbit heart preparation was used as experimental model and subjected to 15 minutes of ischemia followed by 30 minutes of reperfusion, without (group 1), and with Enalaprilat before the ischemia (group 2) and at the beginning of reperfusion (group 3). Left ventricular developed pressure, and end diastolic pressure (diastolic stiffness) were measured and the time constant of isovolumic relaxation (t, Tau) and the ratio between +dP/dtmax and -dP/dtmax were calculated. For the determinations of lactate release and CPK and LDH activities in the perfusate, samples were taken from the coronary effluent for spectrophotometrical measurements. In comparison to the stunned group (group 1) both Enalaprilat preischemia (group 2) and postischemia (group 3) exerted a significant protective effect on the postischemic recovery of contractile state and diastolic stiffness, and attenuated the "hypercontractile" phase in both groups. However Enalaprilat failed to improve myocardial relaxation. Lactate release was also attenuated, but the enzyme activities were not modified.

Adenosine and dipyridamole mimic the effects of ischemic preconditioning

The effects of preconditioning, adenosine and dipyridamole in protecting the systolic and diastolic alterations of myocardial stunning in rabbit hearts were studied. Isovolumic left ventricular developed pressure (LVDP), and end diastolic pressure (LVEDP) were measured. The time constant of relaxation (T) was calculated. Isolated rabbit hearts were subject to 15 min of global ischemia (37 degrees C) followed by 30 min of reperfusion. LVDP and LVEDP stabilized to 55 +/- 5% and 320 +/- 28% of control values respectively (stunned group) T increased early in reperfusion (from 48.2 +/- 3.9 to 97.2 +/- 10 ms P < 0.05) but returned to control value late in reperfusion. When hearts were preconditioned by a single cycle of 5 min of ischemia LVDP and LVEDP stabilized at 89 +/- 3% and 162 +/- 34% of preischemic values respectively (P < 0.05 with respect to stunned group). The change in T was attenuated (62 +/- 6 ms at 5 min of reperfusion, P < 0.05 with respect to stunned group). Hearts treated either with adenosine (800 micrograms/min) or the nucleoside transport blocker dipyridamole (4 micrograms/min) previously to the ischemia, recovered their LVDP to 86 +/- 1% and 82 +/- 3% of preischemic values, respectively (P < 0.05 with respect to stunned group). Adenosine and dipyridamole also attenuated the increase in LVEDP (195 +/- 12% and 197 +/- 10% respectively, P < 0.05 with respect to stunned group).(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic administration of nicardipine attenuates myocardial stunning in isolated rabbit hearts

The purpose of this study was to evaluate the effects of the chronic administration of a calcium channel blocker, nicardipine, on systolic and diastolic alterations occurring during myocardial stunning in isolated rabbit hearts. Rabbits were pretreated with nicardipine 20 mg (O.I.D.) for 30 days. Then hearts were isolated (group II) and compared with control hearts (group I) in their response to 20 min of global ischemia and 30 min of reperfusion. Coronary flow and heart rate were kept constant. Left ventricular isovolumic developed pressure (LVDP), its first derivative (dP/dt), and end diastolic pressure (LVEDP) were measured. After isolation, no statistically significant changes were detected in LVDP, +dP/dtmax, LVEDP, or coronary resistance in hearts of rabbits with or without the pharmacological intervention. Early after the onset of reperfusion, LVDP and +dP/dtmax partially recovered in a similar way in groups I and II. Late in reperfusion LVDP stabilized at 48 +/- 7% in group I and 71 +/- 6% in group II (P < 0.05) and +dP/dtmax stabilized at 56 +/- 7% and 79 +/- 6% (P < 0.05), respectively. Diastolic dysfunction was manifested by a 217 +/- 39% increase in LVEDP (P < 0.05) in group I, and 140 +/- 31% in group II (P < 0.05). The isovolumic relaxation time constant (tau, tau) increased from 70 +/- 5 to 151 +/- 27 ms (P < 0.05), and from 66 +/- 6 to 97 +/- 10 ms. (NS) in groups I and II, respectively at 5 min of reperfusion. This relaxation parameter returned to normal values in the late reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Dissociation between myocardial relaxation and diastolic stiffness in the stunned heart: its prevention by ischemic preconditioning

The effects of myocardial stunning and ischemic preconditioning on left-ventricular developed pressure and end-diastolic pressure (diastolic stiffness) as well as on coronary-perfusion pressure were examined in isolated isovolumic rabbit hearts. The isovolumic relaxation was evaluated, and the time constant of pressure decay during the isovolumic period was calculated. Our experimental protocol comprised: 1) myocardial stunning-global ischemia (15 min) followed by reperfusion (30 min); 2) myocardial stunning-global ischemia (20 min) followed by reperfusion (30 min); and 3) ischemic preconditioning--a single cycle of brief global ischemia and reperfusion (5 min each), before a second ischemic period, of 20-min duration. There was no effect upon systolic and diastolic parameters when 15 and 20 minutes of ischemia were evaluated. In both stunned groups the left ventricular developed pressure first recovered to near control values, but then stabilized at only 60% of the control values. Whereas the isovolumic relaxation time constant was increased after 5 min of reperfusion, and return to control values at late reperfusion, the end diastolic pressure remained elevated during the entire period. Values of dP/dV calculated at common pressure levels, were used as a second index of diastolic stiffness. They were increased after stunning, as also was the coronary perfusion pressure. When the heart was preconditioned with a single episode of ischemia, the systolic and diastolic alterations were completely abolished. We thus concluded that diastolic abnormalities incurred by myocardial stunning consist in both an increase in diastolic stiffness and an early impairment of isovolumic relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of hypocapnic alkalosis on the myocardial contractility of isovolumic perfused rabbit hearts

During acute respiratory alkalosis myocardial contractility first increases but then decreases towards control levels. The mechanism of this response was investigated in isovolumic perfused rabbit hearts. Developed pressure (DP) and its first derivative (dP/dt) were measured before, during and after hypocapnia induced by equilibrating the perfusate with 2% CO2 rather than the 5% used in control. pH of the perfusate (pHo) changed from 7.36 +/- .02 to 7.71 +/- .01. After about 20 s, an increase in DP of about 20% was detected. This increase in contractility is followed by a partial recovery towards control levels. After the partial recovery a new mechanical steady state is reached in about 2 min. Neither 5-[N-ethyl-N-isopropyl]amiloride (EIPA) 10(-6) M, a blocker of the Na+/H+ exchanger, nor 4,4'-diisothiocyanatostilbene-2-2'-disulfonic acid (SITS) 10(-4) M, or 5-[aminosulfonyl]-4-chloro-2-[(2-furanylmethyl)-amino] benzoic acid (furosemide) 10(-4) M, blockers of Cl-/HCO3- exchanger, abolished the recovery in contractility towards control levels. The recovery was not abolished by replacing 50% of extracellular Cl- concentration by either sulfate or gluconate. The lack of blockade of this mechanical recovery in spite of the intervention performed suggests a mechanism other than the exchangers as the cause of the biphasic changes.

Changes in diastolic cardiac function in developing and stable perinephritic hypertension in conscious dogs

The effects of developing perinephritic hypertension (2-3 weeks) and a more stable period of perinephritic hypertension (approximately 14 weeks) were examined on indexes of left ventricular (LV) diastolic function in conscious, chronically instrumented dogs. The complete period of diastole was studied using indexes of isovolumic relaxation (tau), early filling (LV +dD/dt), and stiffness (myocardial stiffness and chamber stress/diameter ratio). During developing hypertension, increased LV end-diastolic pressure, LV end-diastolic stress, peak filling rate, myocardial stiffness, and the stress/diameter ratio increased (p less than 0.05); the time constant tau was not changed. These changes were associated with preserved baseline levels of coronary blood flow (radioactive microspheres) but an impaired coronary vasodilator response to adenosine. Acute administration of phenylephrine in the normotensive dogs caused increases in systolic and diastolic stress and resulted in increases in myocardial stiffness and in the stress/diameter ratio similar to values observed in developing hypertension. During stable hypertension, LV end-diastolic stress, peak filling rate, and both parameters of late-diastolic function (myocardial stiffness and stress/diameter ratio) returned toward control values, but the isovolumic relaxation time constant was increased. Quantitative histological evaluation revealed no increase in stainable connective tissue in dogs with stable hypertension compared with control dogs, and hydroxyproline concentration was not increased in the subendomyocardium, midmyocardium, or subepimyocardium of the dogs with chronic perinephritic hypertension. Thus, in developing hypertension, major alterations in diastolic function were observed that were not structurally related, since these changes 1) could be induced in normal dogs by increasing preload and afterload acutely with phenylephrine and 2) were improved during the ensuing stable period of hypertension.

Inotropic response to norepinephrine is augmented early and maintained late in conscious dogs with perinephritic hypertension

We studied the inotropic responses to intravenous infusions of norepinephrine in nine conscious chronically instrumented dogs before and early (2-4 weeks) in the development of perinephritic hypertension; seven conscious dogs were studied later (approximately 14 weeks), during a more stable phase of hypertension. perinephritic hypertension was associated with a 24% increase in left ventricular (LV) mass during developing hypertension; no further increase was seen during the stable hypertension phase. LV end-systolic stress was increased early (p less than 0.01) but was normalized later. The LV end-systolic stress-volume relation demonstrated an enhanced contractile response to norepinephrine during developing hypertension, which returned toward control later in the course of stable hypertension. The LV dP/dt responses to norepinephrine (0.4 microgram/kg/min) were significantly greater during developing hypertension (7,509 +/- 337 mm Hg/sec, p less than 0.05) compared with the control period (4,737 +/- 286 mm Hg/sec) and returned toward the control value during stable hypertension (5,168 +/- 465 mm Hg/sec). The enhanced inotropic responses to norepinephrine in developing hypertension were preserved in the presence of ganglionic blockade, suggesting that the augmentation was not mediated via reflex mechanisms. These physiological responses were associated with an increase in beta-adrenergic receptor density, but no significant change in basal or maximal adenylate cyclase stimulation occurred during developing hypertension. Thus, in contrast to prior studies in anesthetized animals, the inotropic response to beta-adrenergic stimulation is not depressed in conscious dogs but is enhanced selectively during the development of hypertension and maintained during stable hypertension.

The effects of Bay K 8644 on diastolic function in the dog heart

The effects of increased cytosolic calcium on cardiac mechanics were studied in open chest dogs instrumented with ultrasonic crystals and a miniature pressure transducer. Calcium was increased either by promoting calcium influx with Bay K 8644 (Bay K) or by increasing extracellular calcium concentration. A single dose of Bay K (10 micrograms/kg/min) was administered to each dog. Bay K increased LV systolic pressure, maximal rate of rise of LV pressure (LV + dP/dt), mean velocity of circumferential fiber shortening (Vcf), and calculated LV end-systolic wall stress. The time constant of isovolumic pressure decay (T) was calculated following two different methods: (a) a semilogarithmic method (Tz), and (b) using the linear relation between LV - dP/dt vs LV pressure (T1). Whereas Tz decreased from 31.7 +/- 2.6 to 26.7 +/- 1.7 ms (P less than 0.05), no changes were detected in T1 (46.3 +/- 4.4 vs 50.9 +/- 4.0 ms N.S.) The asymptote value (PB) decreased after Bay K from -9 +/- 2.8 to -22.5 +/- 4.2 mmHg (P less than 0.05). The same results were obtained when the changes in the loading conditions of the heart produced by Bay K were controlled by mechanical manoeuvers or after beta-blockade with propranolol. When calcium chloride was administered in amounts that will produce equal contractile changes as Bay K, a decrease in PB was also observed (from -14.7 +/- 1.6 to -27.7 +/- 6.1 mmHg (P less than 0.05]. Tz decreased from 29.6 +/- 3.6 to 22.5 +/- 2.9 ms (P less than 0.05) and no changes in T1 (52.5 +/- 5 vs 52.4 +/- 7.3 ms, N.S.) were detected. The decrease in the asymptote reported herein could induce a false decrease in the time constant if the altered values of PB are not considered, or another method of calculation of the time constant is used. Neither Bay K nor elevated extracellular calcium concentration modified the diastolic compliance. Changes in loading conditions or a cAMP pathway can be ruled out as a cause of the decrease in PB, since the results were reproduced under controlled loading conditions and beta blockade. These data suggest that increasing cytosolic calcium does not alter either the relaxation rate or the diastolic compliance but does decrease the value toward left ventricular pressure decays.

Application of the systolic stiffness concept to assess myocardial function in developing hypertension

The concept of end-systolic myocardial stiffness permits the quantification of preload effects on fiber shortening and changes in the slope (max Eav) of the end-systolic stress-strain relation, which, if linear, reflect changes in the inotropic state. As an application of this new concept, the end-systolic stress-strain and shortening-afterload relations were evaluated on the basis of data from dogs studied during development of perinephritic hypertension. End-systolic stress-strain relations were linear before and 2 weeks after the induction of hypertension and the end-systolic pressure-diameter relations were not always linear. The shortening-afterload relations obtained directly from raw data points displayed enhanced contractility in the hypertensive state under beta-adrenergic receptor blockade. However, the preload-corrected shortening-afterload relations demonstrated that contractility was unchanged in hypertension. Hypertensive hearts operated at higher preload than normotensive hearts at any afterload levels. This discrepancy between the conventional method without preload-correction and the preload-corrected analysis indicates the importance of preload-correction on shortening-afterload relations in hypertension.

Subendomyocardial exhaustion of blood flow reserve and increased fibrosis in conscious dogs with heart failure

The effects of near-maximal coronary vasodilation were examined in conscious dogs with left ventricular (LV) failure after pressure overload hypertrophy induced by either aortic banding alone or aortic banding plus a peripheral arteriovenous shunt. The findings were compared with results in littermates with compensated LV hypertrophy and with a third group of normal dogs. At rest, there was a marked difference in the intramyocardial distribution of coronary flow, measured with radiolabeled microspheres. The endocardial/epicardial (endo/epi) flow ratio in the LV failure dogs was 0.96 +/- 0.08 as compared with control dogs (1.28 +/- 0.06, p less than 0.05) or dogs with compensated LV hypertrophy (1.23 +/- 0.08, p less than 0.05). During near-maximal coronary vasodilation with adenosine, all groups showed similar increases in subepimyocardial (epi) flow. While significant increases in subendomyocardial (endo) flow during adenosine infusion were seen in the control group (0.88 +/- 0.10 to 3.53 +/- 0.24 ml/min/g) and in dogs with compensated LV hypertrophy (1.12 +/- 0.14 to 3.60 +/- 0.16 ml/min/g), there was no change in endo flow in the LV failure dogs (1.55 +/- 0.20 to 1.71 +/- 0.47 ml/min/g) and a further significant reduction in the endo/epi flow ratio was observed (0.30 +/- 0.06, p less than 0.01). These hemodynamic changes were associated with chronic multifocal interstitial or discrete areas of fibrosis observed preferentially in endo layers. Thus, endo flow reserve is nearly exhausted in dogs with decompensated pressure overload LV hypertrophy, which may induced periodic episodes of endo ischemia resulting in myocyte necrosis and fibrosis, which in turn results in exacerbation of LV failure.

Sympathetic augmentation of cardiac function in developing hypertension in conscious dogs

To determine the alterations in left ventricular (LV) function and the mechanisms involved that occur during the development of perinephritic hypertension, dogs were instrumented with a miniature LV pressure transducer, aortic and left atrial catheters, and ultrasonic crystals to measure LV diameter in the short and long axes and wall thickness. At 2 wk after initiation of perinephritic hypertension, increases (P less than 0.05) were observed in LV systolic pressure, LV end-diastolic pressure, both short- and long-axis end-diastolic diameters, calculated LV end-diastolic volume, stroke volume, global average LV systolic wall stress, first derivative of LV pressure (LV dP/dt), and ejection fraction, whereas mean velocity of circumferential fiber shortening (Vcf) and rate of change of LV short-axis diameter (LV dD/dt) rose but not significantly. At three levels of matched preload and afterload induced by the administration of graded doses of phenylephrine, Vcf, LV dD/dt, and LV dP/dt increased in hypertension compared with the same levels of preload and afterload before hypertension. When the loading conditions in the normotensive and hypertensive dogs were matched, either after ganglionic blockade or beta-adrenergic blockade, both isovolumic and ejection-phase indexes of LV function remained similar before and after hypertension. Thus we conclude that 1) LV function in intact, conscious dogs with early hypertension is enhanced, and 2) the major mechanism for the increase in LV function involves the sympathetic nervous system.

Systolic and diastolic dysfunction during atrial pacing in conscious dogs with left ventricular hypertrophy

To determine the extent to which the hypertrophied left ventricle responds to the chronotropic stress induced by graded atrial pacing rates, we studied conscious, chronically instrumented dogs with severe compensated pressure overload left ventricular (LV) hypertrophy induced by aortic banding in puppies 8-10 weeks of age. At 1-2 years, dogs with severe LV hypertrophy (LV free wall/body wt ratio 6.8 +/- 0.6 g/kg) and sham-operated littermates (LV free wall/body wt ratio 4.0 +/- 0.3 g/kg) were instrumented with ultrasonic dimension crystals to measure LV short axis internal diameter and wall thickness, miniature LV pressure transducers, and aortic and LV catheters. During atrial pacing (240 beats/min) in eight control dogs, LV pressure did not change from 119 +/- 2 mm Hg, and mean velocity of circumferential fiber shortening (VCF) did not change from 1.25 +/- 0.09/sec. In seven dogs with LV hypertrophy, atrial pacing (240 beats/min) decreased systolic LV function; that is, LV systolic pressure decreased (p less than 0.01) by 65 +/- 12 from 254 +/- 14 mm Hg, and VCF decreased (p less than 0.01) by 0.19 +/- 0.03 from 0.97 +/- 0.15/sec. Diastolic dysfunction was also observed in the dogs with LV hypertrophy. In the control dogs during atrial pacing (240 beats/min), LV end-diastolic pressure decreased (p less than 0.01) by 8 +/- 1 from 9 +/- 1 mm Hg, end-diastolic stress decreased (p less than 0.01) by 18 +/- 2 from 22 +/- 2 g/cm2, and the radial myocardial stiffness constant did not change from 5.6 +/- 1.0.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of calcium antagonism on contractile behavior of canine hearts

The cardiovascular effects of prenylamine (P), verapamil (V), and nifedipine (N) were studied in open-chest, anesthetized dogs and in isolated, isovolumic dog hearts perfused at constant coronary blood flow (CBF). These drugs significantly decreased left ventricular pressure (LVP) and its maximal rates of rise (+P) and fall (-P). The tension developed by an isometric segment of the left ventricle and its maximal rates of rise (+T) and fall (-T) also decreased, whereas heart rate (HR) did not show statistically significant differences. Maximal rates of fall (-P and -T) were proportionally more depressed than maximal rates of rise (+P and +T), producing significant increments in the ratios between both maximal velocities (+P/-P and +T/-T). The time constant of LVP isovolumic decay tau was significantly prolonged, either in the whole animal or in isolated perfused hearts. The afterload reduction produced by the compounds can account in part for the increase in +P/-P but not for the increase in +T/-T or for the prolongation of tau. These relaxation indices remained unchanged after comparable myocardial depressions elicited by d,l-propranolol or pentobarbital sodium. It is concluded that calcium antagonist compounds are characterized by an "antirelaxant" effect, not explained by changes in HR, CBF, or loading conditions, and independent from their negative inotropic action.

Myocardial flow distribution. II : Empty beating heart, ventricular fibrillation and cardiac arrest

Myocardial oxygen consumption (MVO2) and coronary blood flow (CBF) distribution were studied in 21 isolated, metabolically supported dog hearts. Measurements of MVO2 and CBF distribution were carried out in three different experimental conditions : empty beating heart (EBH), ventricular fibrillation (VF) and high potassium-induced cardiac arrest (CA). MVO2 was approximately the same in EBH and VF (4.09 +/- 0.77 and 4.28 +/- 0.68 ml O2 min-1 100 g-1 respectively), and significantly lower in the group with CA (2.40 +/- 0.18 ml O2 min-1 100 g-1, P less than 0.05). Total CBF showed no significant differences among the three groups (84 +/- 7 ml/min in EBH; 78 +/- 7 ml/min in VF and 83 +/- 7 ml/min in CA). Subendocardial CBF per unit of tissue mass was significantly lower in hearts with VF (0.43 +/- 0.01 ml/min-1 g-1, P less than 0.05) when tested against the other two groups of experiments (0.69 +/- 0.03 ml min-1 g-1 in EBH and 0.65 +/- +/- 0.04 ml min-1 g-1 in CA). This was also reflected in the endo/epi ratio, that was significantly lower in VF (1.41 +/- 0.07, P less than 0.05) with respect to the other two groups (2 +/- 0.09 in EBH and 2.21 +/- 0.07 in CA). From data presented here we can conclude that cardioplegia, even in absence of hypothermia, is a method that will assure myocardial protection providing : (1) a lower subendocardial MVO2; (2) a higher subendocardial CBF, which helps for a prompt recovery during reperfusion.