Electrophysiologic and anatomic changes in the atrioventricular junction of dogs after direct-current shocks through tissue fixation catheters

Barb-tipped fixation electrode catheters were inserted under fluoroscopic control in the region of the atrioventricular (AV) node in 6 dogs. A series of direct-current shocks (20 to 240 J) were delivered from the electrode catheter to a back plate. Serial electrophysiologic studies were performed before and 2 to 3 weeks after delivery of the shocks. In general, low-energy shocks--20 to 180 J--resulted in predominant damage to the approaches to the AV node, the AV node and common bundle, whereas larger shocks created diffuse damage involving the His bundle and bundle branches. Despite histologic damage to the AV junction, only minimal changes in AV conduction were observed. Thus, there is a large safety margin for AV conduction.

Hybridization studies of chicken liver fatty acid synthetase. Evidence for the participation in palmitate synthesis of cysteine and phosphopantetheine sulfhydryl groups on adjacent subunits

Enzymatically inactive variants of chicken liver fatty acid synthetase have been prepared by specific chemical modification of the active cysteine SH group with iodoacetamide, and the phosphopantetheine SH group with chloroacetyl-CoA. Hybridization of each of these variants with the unmodified enzyme yielded (modified)-(unmodified) hybrid dimers which possessed 50% synthetase activity. A 50% active (iodoacetamide-modified)-(chloroacetyl-CoA-modified) hybrid dimer was also demonstrated by recombination of these variants with each other. These results indicate that the two functional sites on the synthetase are independently active, and that each is comprised of a cysteine SH group from one subunit and a complementary phosphopantetheine SH group from the other subunit as depicted by the head-to-tail arrangement proposed by Wakil and co-workers (Wakil, S. J., Stoops, J. K., and Joshi, V.C.

The role of essential fatty acids and prostaglandins in cercarial penetration (Schistosoma mansoni)

We used rat skin membranes to test the putative role of prostaglandins (PG) and essential fatty acids (EFA) in the penetration response of Schistosoma mansoni cercariae. To examine the effects of EFA on cercarial penetration an EFA-deficient rat model was used. Dams were fed an EFA-deficient diet during lactation and the pups were weaned to this diet. Cercarial penetration of EFA-deficient rat skin membranes was not reduced from control levels until 12 wk on the diet. At this time a decrease of 64.3% was observed. This decrease remained constant up to 16 wk, after which the study was terminated. Other normal rats were treated with 20 mg/kg ibuprofen, a PG inhibitor, to examine the role of PG in the penetration response. Treated rat skin contained a mean of 2 micrograms ibuprofen per 30 mm3 of skin (25-mm skin disc) at 1.5 hours post-injection. Skin from treated rats inhibited penetration by over 81%. These studies indicate that skin EFA and PG may have a critical role in the completeness of penetration by cercariae through the skin, although it is not clear whether cercarial or host PG are involved in the penetration response.

The role of prostaglandins in cercarial (Schistosoma mansoni) response to free fatty acids

In examining the structure-activity relationship of a diverse group of chemicals reported to prevent cercarial penetration after topical application, we noticed a moiety that was common to free fatty acids and prostaglandins. Because unsaturated fatty acids have been reported to stimulate cercarial penetration, we hypothesized that cercarial stimulation by skin and fatty acids may invoke prostaglandin mechanisms in cercariae, skin, or both. Thus we compared the stimulation of cercariae by a series of essential and nonessential fatty acids and demonstrated an inhibition of this response by ibuprofen and aspirin, known cyclo-oxygenase inhibitors, and by 13-azaprostanoic acid, a potent antagonist of the thromboxane/endoperoxide receptor. These data led us to postulate a major role for prostaglandins in the cercarial penetration response.

Effect of Substrate Concentration and Organic and Inorganic Compounds on the Occurrence and Rate of Mineralization and Cometabolism

Isopropyl N -phenylcarbamate (IPC) at 400 pg and 1 μg/ml was mineralized in samples of sewage, but only the lower concentration was mineralized in lake water samples in a 50-day period. IPC at 1 μg/ml disappeared from lake water, but it was converted to organic products. Mineralization of IPC at 400 pg/ml in lake water was enhanced by additions of inorganic nutrients or a mixture of nonchlorinated water pollutants but not by yeast extract or mixtures containing aromatic compounds or excretions of primary producers. The mineralization of 200 pg of 2,4-dichlorophenoxyacetate per ml of lake water was not affected by additions of low levels of yeast extract or compounds excreted by primary producers but was enhanced by low concentrations of mixtures of water pollutants. It is suggested that some chemicals that are found to be converted only to organic products, presumably by cometabolism, in tests using the concentrations commonly employed in laboratory evaluations may be mineralized at the lower concentrations prevailing in natural waters.

Prostatic cancer--II. Inhibitors of rat prostatic 4-ene-3-ketosteroid 5 alpha-reductase derived from 6-methylene-4-androsten-3-ones

The studied 6-methylene-4-androsten-3-ones proved to be significantly inferior to 6-methylene-4-pregnene-3,20-dione and its 17-acetoxy derivative described in Part 1 as inhibitors of 4-ene-3-ketosteroid 5 alpha-reductase [1] in vitro. Surprisingly, the 6-methylene derivative of testosterone was only weakly active until acetylated, when an effective inhibitor was obtained. Etherification of the hydroxyl-group, its replacement by a hydrocarbon chain, or introduction of a substituent at C17 or on the methylene group led to virtual loss of activity. 17 alpha-Chloro-6-methylene-4-androstene-3-one had ca 60-70% of the potency of progesterone, but was inactive as enzyme inhibitor in explants of rat prostate in tissue culture and in in vivo studies. 6-Methylenetestosterone acetate was weakly active as enzyme inhibitor in explants of human prostate in tissue culture and produced a histological picture closely resembling testosterone and differing from that of cyproterone acetate. In vivo in the rat it had 80% of the androgenic activity of testosterone propionate. The foregoing data have been used to define some structural characteristics necessary for enzyme inhibition and to draw some conclusions regarding the architecture of the androgen and progesterone receptors and of the enzyme active site.

Extent of atrial participation in atrioventricular-reciprocating tachycardia

Twenty-one patients with atrioventricular (AV) bypass tracts underwent electrophysiologic studies. The bypass tract was left-sided in 15 patients, septal in five and right-sided in one patient. Orthodromic AV-reciprocating tachycardia was induced in all 21 patients, with a mean tachycardia cycle length of 342 +/- 59 msec. The introduction of single stimuli in the high right atrium during tachycardia resulted in simultaneous dissociation of the high right atrial and low septal atrial electrograms in nine patients. In six patients, high right atrial overdrive pacing during tachycardia resulted in simultaneous dissociation of the high right atrial and low septal atrial electrograms for two to five consecutive beats. All patients in whom the low septal atrial electrogram was dissociated from the tachycardia had a left-sided bypass tract. In no patient was the coronary sinus atrial electrogram dissociated from the tachycardia by high right atrial pacing. Dissociation of the low septal atrial electrogram (as recorded in the His bundle electrogram) from AV-reciprocating tachycardia suggests that the portion of the right atrium adjacent to the AV node may not be a necessary link in the tachycardia circuit. This observation suggests that the site of entry of left-sided impulses into the AV node may be different from that of right-sided impulses.

Left ventricular volumes determined by two-dimensional echocardiography in a normal adult population

The purpose of this study was to determine normal population volume variables of the left ventricle as determined by different algorithms currently available. Two-dimensional echocardiography was prospectively performed on 52 normal volunteers to determine normal left ventricular volume and ejection fraction as a prerequisite to their clinical application. All echocardiograms were performed using a commercially available two-dimensional phased array sector scanner. Three algorithms were applied to three views in various combinations. Ejection fraction calculations were found to be reliable, reproducible and independent of the algorithm employed. Left ventricular volumes were larger in men than in women (probability [p] less than 0.005) despite correcting for body surface area, indicating the need for separating patients according to sex. The Simpson's rule algorithm resulted in smaller values for left ventricular volume than did any of the area-length algorithms and the data were the most reproducible as judged by intraobserver variation. The single plane area-length methods are clinically useful because they are simple, rapid to execute and reliable. Ejection fraction calculation was independent of the algorithm employed.

Normal left atrial function determined by 2-dimensional echocardiography

To obtain normal values for left atrial function noninvasively, volumes of the left atrium and ventricle were calculated in 52 volunteers by 2-dimensional echocardiography. A light pen digitizing and computation system, controlled by a microprocessor, was used to outline the left atrium and ventricle in orthogonal apical views. Then, to calculate end-systolic and end-diastolic atrial and ventricular volumes, a modified Simpson's rule formula was used. End-systolic left atrial volume (mean +/- standard deviation) was 37 +/- 11.7 ml or 21 +/- 6.6 ml/m2. The change in left atrial volume from end-systole to end-diastole was 24 +/- 7.6 ml or 13.5 +/- 4.3 ml/m2, which represented 37 +/- 12.9% of left ventricular stroke volume. The mean fractional emptying of the left atrium was 65 +/- 8.9% and the conduit volume was 41 +/- 14.0 ml or 23 +/- 7.9 ml/m2. These values are similar to those reported in studies in which left atrial function was calculated from contrast angiography.

Serological mass survey for early detection of nasopharyngeal carcinoma in Wuzhou City, China

A serological mass survey was carried out in Wuzhou City of the Guangxi Autonomous Region, China. Sera were collected from 12,932 persons between the ages of 40 and 59. The positive rate of VCA/IgA antibody-positive person was 5.3%, but no EA/IgA antibody was found in sera from VCA/Iga-negative persons. Thirteen and nine nasopharyngeal carcinoma (NPC) patients were detected from the VCA/Iga and EA/IgA antibody-positive persons, respectively. With the present combination method the detection rate of NPC for 12,932 persons was 100.5/100,000 and for 680 VCA/IgA antibody-positive persons it was 1,900/100,000. Thus, the rate was twice and 37 times higher, respectively, than the annual incidence rate of NPC in persons of the same age group from 1975-1978 in Wuzhou City. Of 13 NPC patients, 9 were in stage I (70%) and 4 in stage II (30%). Therefore, it is possible to reduce the mortality rate of NPC in Wuzhou City by radiotherapy of NPC patients in the early stage of the disease. The present results further suggest that EB virus is closely associated with NPC.