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Isolated rabbit papillary muscles that do not present pacemaker activity under physiological conditions develop a spontaneous activity in the presence of 2 mmol/l BaCl2. Ba-induced contractions were unaffected by high concentrations of the Na antagonist procainamide (10(-5) mol/l). Tetrodotoxin (10(-5) mol/l), a specific blocker of the fast Na current, only slightly increased the amplitude of contractions. In contrast, the calcium entry blockers nifedipine, diltiazem, and verapamil strongly depressed the mechanical activity in a time- and dose-dependent manner. The concentrations that decreased the amplitude and frequency of contractions by 50% were determined. The order of potency was nifedipine much greater than diltiazem greater than or equal to verapamil. Ba-induced automaticity is a particularly useful model on which the potency of calcium entry blockers could be assessed.

The effect of Bay K 8644 on contractile responses to angiotensin II (AII) was investigated in rabbit aorta. Bay K 8644 alone did not elicit contraction while contractile responses to AII were enhanced at low concentrations (10(-8), 3 X 10(-8), 10(-7) M) and depressed at a higher concentration (10(-6) M). The potentiating effect was always observed and increased after treatment by phentolamine. These findings suggest that Bay K 8644 activates calcium channels operated by angiotensin receptors.

The specificity of the alpha-adrenergic blockade by trifluoperazine was tested in pithed rats. Trifluoperazine reduced the pressor effects of (-)-noradrenaline. The log dose-response curve to methoxamine, an alpha 1-agonist, was shifted to the right whereas the vasopressor responses to BHT-920, an alpha 2-agonist, were unaffected by trifluoperazine. It was concluded that trifluoperazine acts as a peripheral vascular alpha 1-antagonist in the rat.

Extracorporeal shock wave lithotripsy is a new therapeutic technology that has received instant and widespread acceptance. The history and technical aspects of the procedure are presented, but most importantly, the authors discuss radiology's role and note the importance of management's awareness of the potential impact on departmental fiscal, equipment and personnel resources.

It has been suggested that complex ventricular arrhythmias commonly occur in hypertensive patients with left ventricular hypertrophy. We have previously demonstrated that coronary artery ligation in anesthetized spontaneously hypertensive rats (SHR) and their normotensive controls (WKY) resulted in a significantly increased incidence and duration of ventricular fibrillation in SHR compared with WKY. The object of the present study was to characterize the structural and electrophysiological abnormalities in hypertrophied hearts, associated with the occurrence of arrhythmias. We used a double tissue bath in which a ventricular strip was exposed simultaneously to normal and to altered conditions (low pH, hypoxia and high potassium). Electrical activity recorded using standard micro-electrode techniques showed the occurrence of arrhythmias in all preparations and the development of major alterations in conduction (a conduction block appeared at 11 +/- 1 mn in SHR vs 16 +/- 1 mn in WKY, p less than 0.05), and maximal upstroke velocity (Vmax values before and 3 mn after the beginning of ischemia were 229 +/- 12 to 46 +/- 7 v/s for the SHR and 227 +/- 10 to 106 +/- 12 v/s for the WKY; p less than 0.001). These changes were associated in hypertrophied ventricles with a marked sub-endocardial collagen fibrosis as estimated by the use of automated image analysis (subendocardial collagen density = 4.39 +/- 0.34 p. 100 in SHR vs 1.66 +/- 0.15 p. 100 in WKY; p less than 0.001). Action potential duration measured using conventional glass micro-electrodes in a single chamber tissue bath revealed a highly significant difference (p less than 0.001) in APD 90 p. 100 of papillary muscles between SHR (114.7 +/- 2.8 ms) and WKY (76.9 +/- 1.7 ms). The addition of tetra-ethylammonium to block potassium channels induced triggered activity arising from early afterdepolarizations only in muscles hypertrophied SHR hearts.(ABSTRACT TRUNCATED AT 250 WORDS)

Global forebrain ischemia was induced in unanesthetized rats by electrocauterization of the vertebral arteries and transient occlusion of the common carotid arteries for 30 minutes. Local cerebral blood flow (l-CBF), cortical tissular pO2 (tpO2), electrocorticogram (ECoG), mean arterial pressure, pH and blood gas determinations and neurologic deficit were evaluated during and after ischemia. Cerebral ischemia induced a substantial decrease in l-CBF and tpO2 and the ECoG was flattened. One hour after ischemia, the neurologic deficit was at its maximum, l-CBF was still decreased and ECoG depressed. Twenty-four hours later, the neurologic deficit was still present but ECoG, l-CBF and tpO2 had returned to their preischemic values. Treatments with naloxone were performed during, after or during and after ischemia. When naloxone was administered during or after ischemia, postischemic neurologic deficit was not influenced by the treatment. A slight but significant improvement of the neurologic score was observed when naloxone was injected during ischemia and infused thereafter. Our results show that this experimental model of cerebral ischemia is suitable for quantification of neurologic alterations during the postischemic period. The slight improvement observed with naloxone suggests that endogenous opioids may have a minor role in the neurologic consequences of ischemia.

Cardiac hypertrophy and hypertension are major elements in sudden cardiac death in patients with coronary artery disease. To investigate in animals the hypothesis that left ventricular hypertrophy (LVH) and/or hypertension increase the incidence of severe ventricular arrhythmias, we have undertaken a 30 min period of coronary artery ligation in anaesthetized spontaneously hypertensive rats (SHR), normotensive (NT) Wistar Kyoto (WKY) and Wistar (W) rats. Mean systolic blood pressure (SBP) was 190 +/- 4 mmHg in SHR vs 123 +/- 5 mmHg in WKY and 116 +/- 4 mmHg in W (p less than 0.001). LVH index was 2.81 +/- 0.04 in SHR vs 196 +/- 0.03 in WKY and 1.65 +/- 0.05 in W (p less than 0.01). Incidence (IVF) and duration (DVF) of ventricular fibrillation were significantly more elevated in SHR than in NT rats. IVF was 100 p. 100 in SHR vs 36 p. 100 in WKY and 27 p. 100 in W (p less than 0.001); DVF was 61 +/- 17 s in SHR vs 6 +/- 6 s in WKY and W (p less than 0.001). In addition the calcium channel blocker nicardipine (N) has been administered orally to SHR either chronically during eight weeks (20 mg/kg-1 per os twice daily) or acutely as a single dose of 20 mg/kg. After long term treatment (LT) with N the LVH index and SBP were significantly reduced when compared to vehicle treated (VT) SHR; whereas a single administration of N (AT) only decreased SBP without affecting LVH.(ABSTRACT TRUNCATED AT 250 WORDS)

LF 2.0254 is a new 1.4 dihydropyridine that relaxes vascular smooth muscles by blockade of calcium entry mediated by depolarisation. In rabbit aortas contracted by KCl (15 to 55 mM) or CaCl2 (2 mM), LF 2.0254 differs markedly from nifedipine and nicardipine because of its slow onset of action, the inhibitory effect increasing with the duration of tissular contact. LF 2.0254 has only slight negative chronotropic and inotropic effects on isolated guinea-pig atria as well as in anesthetized dogs after intravenous administration. Furthermore, in open-chest anesthetized dogs, LF 2.0254 decreases mean arterial blood pressure and since cardiac output is maintained total peripheral resistance is decreased. LF 2.0254 administered orally to perinephritic hypertensive dogs (0.1 and 0.3 mg/kg) and to spontaneously hypertensive rats (0.3 to 10 mg/kg) induces a more pronounced and long-lasting hypotensive action than nifedipine. In conclusion, these results suggest that LF 2.0254 could be useful in the treatment of hypertension associated or not with cardiac insufficiency.

Effects of two dihydropyridine derivatives, nifedipine and nicardipine, on systolic blood pressure and heart rate in adult (4- to 5-month-old) spontaneously hypertensive rats (SHR) were studied in comparison with those in aged (11- to 12-month-old) SHR. Both calcium channel blockers induced similar dose-dependent hypotensive effects in 4- to 5-month- and 11- to 12-month-old SHR. The maximal hypotensive action of both calcium channel blockers was delayed in aged SHR compared to adult SHR. Nicardipine induced a similar reflex tachycardia in adult and aged SHR. In contrast to nicardipine there was no increase in heart rate after administration of nifedipine in aged SHR at same hypotensive effects. It is concluded that nifedipine and nicardipine are potent antihypertensive agents in aged SHR which differently affect heart rate.

The effect of naloxone upon neurologic deficit was evaluated in a model of transient forebrain ischemia in rats. Awake male Wistar rats were subjected to a 30 minute ischemia by occluding both common carotid arteries 8 days after cauterizing vertebral arteries. Administration of naloxone 1 or 5 mg/kg iv 10 minutes after carotid occlusion or 1 mg/kg iv one hour after clamp removal failed to reduce immediate and tardive neurologic postischemic deficits. On the other hand, in rats treated by a dose of 1 mg/kg naloxone 10 minutes after carotid occlusion and perfused with an additional dose of 2 mg/kg/h for 80 minutes, neurologic score was improved one hour after ischemia. However mortality was not decreased whatever was the modality of naloxone administration. This result confirms previous data showing that naloxone exerts a protective effect when given at sufficiently high dosage.