The effects of multiple increases in sinus cycle length on sinus node recovery time (SNRT) were examined in 5 dogs. Pacing was performed from the left atrial appendage for 30 and 60 seconds using at least 4 different pacing cycle lengths selected between 230 and 620 msec. Each dog received propranolol (1 mg/kg, IV) prior to any measurements. The effects of increases in sinus cycle length on SNRT were first assessed during 2 levels (4 and 8 Hz) of continuous vagal stimulation. From a control cycle length of 439 +/- 28 msec (mean +/- SE), the vagal stimulations lengthened the sinus cycle lengths to 604 +/- 10 msec and 758 +/- 16 msec respectively. Sinus cycle length was then prolonged by combined muscarinic and beta-receptor blockade resulting in a sinus cycle length of 549 +/- 9 msec. Autonomic blockade plus verapamil (3-10 mg IV) resulted in sinus cycle lengths of 612 +/- 14 and 721 +/- 18 msec respectively, which were not significantly different from those obtained with vagal stimulation. Data relating SNRT to the sinus cycle length, pacing cycle length, duration of pacing and the negative chronotropic interventions used to achieve the changes in the sinus cycle length were analyzed via covariance analysis. The results demonstrate that the single most important determinant of SNRT is the sinus cycle length. Furthermore, equivalent increases in sinus cycle length whether obtained by vagal stimulation, autonomic blockade or intravenous verapamil results in SNRTs that are not significantly different. Therefore, in the sinus node, changes in the rate of pacemaker activity, regardless of how they are achieved, will largely determine the changes in SNRT.

Adrenergic beta-Antagonists↗

PubMedDate not supplied

Differential effects of sympathetic activity on AV junctional automaticity and AV conduction.

Rapid ventricular response during episodes of supraventricular tachycardia are often followed, on abrupt cessation of the tachycardia, by prolonged pauses terminated by a sluggish and sometimes erratic escape of a supraventricular pacemaker. Such chronotropic-dromotropic paradoxes are readily reproduced in the animal laboratory following elimination of the sinus node and bilateral decentralization of the stellate ganglia and vagi. This study examined whether left stellate stimulation (0.5, 1, 2, 4, 8 and 16 Hz) or lack thereof differentially affected AV junctional automaticity and AV conduction. In the absence of any sympathetic neural activity (maximal sympathetic deficit), the AV junctional rate averaged a mere 22 +/- 2 percent of its peak performance, whereas under the same conditions, anterograde AV conduction averaged 73 +/- 5 percent and retrograde VA conduction 56 +/- 13 percent of their respective peak performances. On comparing the response curve (normalized responses) for AV junctional automaticity with that obtained for anterograde AV conduction the differences were significant at all frequencies between 0 and 4 Hz. Retrograde VA conduction (as assessed by the fastest ventricular pacing rate still conducted 1:1 to the atria) was always significantly less than anterograde AV conduction (as assessed by the fastest atrial pacing still conducted 1:1 to the ventricles). These results indicate that AV junctional automaticity is considerably more affected by sympathetic deficit than are either anterograde or retrograde AV conduction. In other words, AV junctional automaticity is far more dependent upon sympathetic input than AV conduction. While sympathetic influence is critical to the escape and maintenance of AV junctional automaticity both anterograde and retrograde AV conduction are remarkably resilient even under conditions of severe sympathetic deficit.

Animals↗

PubMedDate not supplied

Cardiac catheterization and angiographic analysis computer applications.

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Angiocardiography↗

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Marketing a new program begins inside your own hospital.

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Alcoholism↗

PubMedDate not supplied

Systematic implications of chromosomal data from two insular species of Peromyscus from the Gulf of California.

G- and C-banded karyotypes for two insular species of deer mice, Peromyscus slevini and P. sejugis, are described and analyzed relative to the evolutionary relationship of these species to and their inclusion within the P. maniculatus species group. The chromosomal phenotype of P. slevini is unique among all banded karyotypes reported for Peromyscus, and comparison with published karyotypes suggests that P. slevini has systematic affinities with either the P. boylii or P. mexicanus species groups. The karyotypic data for P. sejugis clearly align these mice with P. maniculatus and provide a diagnostic character that supports the specific distinction between these taxa.

Animals↗

PubMedDate not supplied

Effect of halothane on contractile function of ischemic myocardium.

Effects of halothane on the force of myocardial contraction and energy demand-supply balance (NADH fluorescence) were studied in two rabbit heart preparations--the interventricular septum perfused through the septal artery at various flow levels, and a Langendorff whole-heart preparation with ischemia caused by graded reduction of perfusion pressure. The septum experiments showed that halothane [1.2% = 1.5 minimum alveolar concentration of anesthetic preventing movement response to a noxious stimulus (MAC)] increased NADH fluorescence (+9%, p less than 0.02) at a normal level of perfusion (3 ml/g/min) and, at the same time, decreased it (-6%, p less than 0.02) when myocardial energy balance deteriorated from severe hypoperfusion (0.2 ml/g/min). The inhibitory effect of halothane on developed systolic tension was less pronounced at the low (ischemic) level of myocardial perfusion as compared with the high level--leads to 24% (0.2 ml/g/min) vs. leads to 38% (3 ml/g/min), p less than 0.025. However, if control and halothane values of developed tension were compared at equi-NADH levels (the same state of energy balance), the depressive effect of halothane on the force of myocardial contraction was not less pronounced in severe energy imbalance. Similar results were obtained in the Langendorff preparation experiments. The results suggest that halothane partially restores energy balance in hypoperfused myocardium; however, at the normal level of perfusion, its effect is in an opposite direction. Halothane depresses contractility in the hypoperfused myocardium to a lesser degree than at the normal level of myocardial perfusion. This effect is probably determined by the interaction of two influences: direct depressive effect of the agent on contractile mechanisms, and indirect positive inotropic effect due to improvement in energy balance.

Animals↗

PubMedDate not supplied

Homology of partial primary sequences between alpha-enolase and a suppressive lymphokine from human T cells.

A relationship is described between TS--a human suppressive lymphokine produced by hybridoma T cells--and alpha-enolase from the U937 monocyte human cell line. A strong homology (92%) was observed by comparing the internal amino acid sequences of 6 TS peptides, corresponding to 52 residues, with the complete sequence of alpha-enolase. The molecular masses of these two molecules were found to be of about 47 kDa and both were detected with the same monoclonal antibody to TS. In contrast, no immunosuppressive activity was detected with the purified enolase fraction, whereas TS did not show any enolase activity. A suppressive monokine secreted by U937 cells was found to be unrelated with TS. Theses results suggest that the TS immunosuppressive factor despite its absence of enzyme activity, belongs to the enolase family.

Amino Acid Sequence↗