Significance of Ventricular Pacing Site in Manifest Entrainment During Orthodromic Atrioventricular Reentrant Tachycardia with Left-Sided Accessory Pathway

We examined entrainment by ventricular pacing in six patients during orthodromic atrioventricular reentrant tachycardia (AVRT) utilizing a left-sided lateral accessory pathway. Constant fusion and progressive fusion were demonstrated in all patients by left ventricular pacing during tachycardia, but in none of the patients by right ventricular pacing. When left ventricular pacing was performed during AVRT, the antidromic wave front from the pacing impulse (n) collided with the orthodromic wave front of the previous pacing beat (n - 1) within the ventricle, therefore, constant fusion and progressive fusion were demonstrated in the surface electrocardiographic QRS complexes. On the other hand, when right ventricular pacing was performed during orthodromic AVRT, the antidromic wave front from the pacing impulse (n) collided with the orthodromic wave front of the previous paced beat (n - 1) within the normal atrioventricular pathway, and constant fusion and progressive fusion were therefore not demonstrated. These phenomena were explained by the relationship of the ventricular pacing site and the reentrant circuit. This study demonstrates the importance of the pacing site in manifest entrainment of orthodromic AVRT during ventricular pacing.     

The ionic mechanism of phenylephrine-induced rhythmic contractions in rabbit mesenteric arteries treated with ryanodine

Phenylephrine induces endothelium-independent rhythmic contractions in ryanodinetreated rabbit mesenteric arteries. To elucidate the ionic mechanism of this rhythmic behaviour, rabbit mesenteric arterial rings were suspended in an organ chamber for isometric tension studies. Yohimbine, propranolol, and atropine had no effect on these contractions, minimizing the possibility that transmitter release from nerve terminals was involved. Additionally, the oscillatory contractions were not altered by diphenhydramine, cimetidine, and indomethacin, thus ruling out the involvement of histamine and prostaglandins. This oscillatory response was completely abolished after the removal of extracellular Ca 2+, as well as after Ca 2+ channel blockade by diltiazem or nifedipine. Sparteine and quinidine, Ca 2+-activated K+ channel antagonists, also abolished the oscillation. In contrast, tetraethylammonium and 3,4-diaminopyridine, voltage-dependent K+ channel antagonists, augmented the response. Glibenclamide, an antagonist of the ATP-sensitive K+ channel, had no effect on the rhythmic contractions. These results suggest that the rhythmic contractions observed in rabbit mesenteric arteries after ryanodine treatment were caused by the movement of Ca 2+ and K+ across the plasmalemma via the voltage-dependent Ca 2+ channel and the Ca 2+-activated K+ channel, respectively.     

Primitive neuroectodermal tumor of the adrenal gland

We report a rare case of primitive neuroectodermal tumor arising from adrenal gland in adulthood, diagnosed preoperatively as having non-functional adrenocortical adenoma. Laparoscopic adrenalectomy was performed. Immunohistological examination revealed the definite diagnosis as primitive neuroectodermal tumor of the adrenal gland. Although primitive neuroectodermal tumor is a highly malignant neoplasm, there is no evidence of local recurrence and distant metastasis 16 months after surgery.     

The Inhibitory Effects of Cephalosporin and Dipeptide on Ceftibuten Uptake by Human and Rat Intestinal Brush-border Membrane Vesicles

Abstract— The types of inhibitory effects caused by compound V (an analogue of ceftibuten) and alanylproline (dipeptide) on the uptake of ceftibuten by brush-border membrane vesicles (BBMV) prepared from human and rat small intestine were analysed. In the presence of an inward H⁺-gradient, the initial uptake rate of ceftibuten by both human and rat intestinal BBMV was concentration-dependent with apparent K_m and V_max values of 0·35 min and 2·052 nmol (mg protein)^?1 min^?1 for human BBMV, and 0·50 mm and 3·056 nmol (mg protein)^?1 min^?1 for rat BBMV, respectively. For both human and rat BBMV, kinetic analysis by Dixon and Lineweaver–Burk plots demonstrated that the uptake of ceftibuten was competitively inhibited by compound V, whereas inhibition by alanylproline was noncompetitive or partially competitive. These results suggest that there is a stereospecific transport system which is common to ceftibuten and compound V, and that this system is not identical to the carrier system for the dipeptide, alanylproline.     

Narrow QRS Complex Tachycardia with Atrioventricular Dissociation

We describe the case of a 22-year-old man who had frequent episodes of narrow QRS complex tachycardia with atrioventricular dissociation. The ECG during sinus rhythm showed normal PR and QRS intervals, but it showed a left bundle branch block configuration during atrial pacing or after injection of verapamil. An electrophysiological study demonstrated that the patient had nodoventricular Mahaim fibers. The narrow QRS complex tachycardia was explained by a circuit involving antegrade conduction via the atrioventricular nodo-His axis and retrograde conduction via the nodoventricular bypass tract.     

Differential Effects of Dopamine Antagonists on Evoked Dopamine Release from Slices of Striatum and Nucleus Accumbens in Rats

The effects of dopamine-receptor antagonists on electrically-evoked dopamine release were compared in the nucleus accumbens and striatal slices of rats. (-)-Sulpiride induced a concentration-dependent increase in the evoked dopamine release from both regions, the increase in the nucleus accumbens being significantly greater than that in the striatum. Clozapine also increased evoked dopamine release from the nucleus accumbens, but not from the striatum. The haloperidol-induced increase in evoked dopamine release from the nucleus accumbens was less than that from the striatum. These findings indicate that, in terms of dopamine transmission, (-)-sulpiride and clozapine, but not haloperidol, predominantly affect the nucleus accumbens rather than the striatum. We have previously reported that the contribution of D₃ receptors to the regulation of dopamine release from dopamine nerve terminals is much greater in the nucleus accumbens than that in the striatum. (-)-Sulpiride and clozapine have relatively higher affinity for D₃ receptors than does haloperidol. The regional differences in responsiveness of dopamine release to dopamine antagonists could be due to the different affinities to D₂ or D₃ receptors of the dopamine antagonists.