Effects of derivatives of NGP 1-01, a putative calcium channel antagonist, on electrically stimulated guinea-pig papillary muscle.

In earlier work we have reported calcium antagonistic properties for the polycyclic compound NGP 1-01. We now have derivatized NGP 1-01 by side-chain substitution to obtain ten novel aromatic and aliphatic imino-keto and amino-ether compounds. Electrophysiological tests were conducted on these compounds using isolated guinea-pig papillary muscle preparations to record calcium-mediated (slow) action potentials (APs). The lipophilicities of the compounds, expressed as chromatographically determined RM values, were measured and the molecular surface areas calculated. Several derivatives showed increased activity compared with NGP 1-01. All compounds with aromatic side-chains (benzyl, phenethyl, phenylpropyl) were active (concentrations required for complete suppression of the AP varied between 1 x 10(-5) M and 5 x 10(-5) M) and compounds with shorter (methyl, butyl) aliphatic side-chains were inactive whilst activity increased dramatically in those compounds with octyl side-chains. Lipophilicity and calculated molecular volumes correlated linearly and bulkier, more lipophilic molecules had increasing activities in the electrophysiological assay. We therefore conclude that bulky substituents on the nitrogen atom increase calcium antagonistic activity in this series of compounds.

Structure-activity relationships of polycyclic aromatic amines with calcium channel blocking activity.

8-Benzylamino-8, 11-oxapentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane (1) inhibits the calcium current in L-type calcium channels. A series of nitrobenzylamines (2, 3, 4), methoxybenzylamines (5, 6, 7), methylpyridines (8, 9, 10), and a phenylhydrazine derivative (11) of 8,11-oxapentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane was synthesized. By substituting the 8,11-oxapentacyclo-[5.4.0.0(2,6).0(3,10).0(5,9)]undecane skeleton with 3-hydroxyhexacyclo-[6.5.0.0(3,7).0(4,12).0(5,10).0(9,13)]tridec ane (12), 8,13-dioxapentacyclo[6.5.0.0(2,6).0(5,10).0(3,11)]tridecane- 9-one (13), and pentacyclo-[5.4.0.0(2,6).0(3,10).0(5,9)]undecane (14), the effect of the polycyclic skeleton could also be investigated. Increased inhibition of calcium current was observed with aromatic substitution (especially ortho and meta substitution) in the pentacycloundecane series. The calcium channel activities of the methoxy compounds were slightly higher than those of the corresponding nitro compounds while a definite decrease in activity was observed for the phenylhydrazine and aminomethylpyridine derivatives. Increased inhibition of the calcium current was also observed for structures in which the polycyclic 'cages' were enlarged. Structure-activity relationships in this series of compounds therefore appear to be dominated by geometric or steric constraints.

A unified nomenclature for short-chain peptides isolated from scorpion venoms: alpha-KTx molecular subfamilies.

Peptidyl toxins are used extensively to determine the pharmacology of ion channels. Four families of peptides have been purified from scorpion venom. In this article, the classification of K+-channel-blocking peptides belonging to family 2 peptides and comprising 30-40 amino acids linked by three or four disulfide bridges, will be discussed. Evidence is provided for the existence of 12 molecular subfamilies, named alpha-KTx1-12, containing 49 different peptides. Because of the pharmacological divergence of these peptides, the principle of classification was based on a primary sequence alignment, combined with maximum parsimony and Neighbour-Joining analysis.

Comparison and characterization of the venoms of three Parabuthus scorpion species occurring in southern Africa.

Parabuthus transvaalicus, P. granulatus, and P. villosus are three medically important scorpion species occurring in southern Africa which can cause severe envenoming among people. In contrast to many other genera, no data is available on the venom composition of scorpions belonging to the genus Parabuthus. Here we have investigated the components which may contribute to the venomous potential. The constancy of venom composition within each of the three species and between the three species was investigated by means of gel filtration chromatography. The venoms of the three species each were characterized by a constant and typical elution pattern, resulting in a 'gel filtration fingerprint' which allows distinction between each species. It appears that certain components in the venoms are common to either all three species, or to two of the three species. This points to a clear interspecies relationship within the genus. We also describe the isolation and characterization of some of the polypeptide toxins present in the venoms of P. villosus, P. transvaalicus and P. granulatus by means of reversed phase chromatography and screening of the toxic components on voltage-activated potassium and sodium channels. Our results confirm that toxins which inhibit potassium channels and alter sodium channel gating are present in the venoms studied.

Enantiomeric resolution of the calcium channel antagonist 8-benzylamino-8,11-oxapentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]unde cane (NGP 1-01).

We report the enantiomeric resolution and results of studies designed to probe possible enantiospecific calcium channel activity of 8-benzylamino-8,11-oxapentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undec ane (NGP 1-01), a known polycyclic benzylamino calcium channel antagonist. R-(-)-acetylmandeloylchloride was used to generate the two diastereomers which were separated by conventional column-chromatography. Hydrolysis of the separated amide diastereomers was achieved in 10% oxalic acid/dichloromethane with silica gel as catalyst and yielded the resolved enantiomers of NGP 1-01. Enantiomeric purity was assessed by in situ derivatization of the individual enantiomers with 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl isothiocyanate (TAGIT) and HPLC analysis. A standard C18 column was used and the enantiomeric purity was found to be 98.5% and 96.63% for the (+)- and (-)-enantiomer, respectively. The enantiomers exhibited similar activity profiles, for calcium channel antagonism and also did not differ from the racemic mixture, suggesting that NGP 1-01 has very weak or no stereo-selectivity in the calcium channel assay used.

The biological activity of selected cyclic dipeptides.

Cyclic dipeptides are widely used as models for larger peptides because of their simplicity and limited conformational freedom. Some cyclic dipeptides have been shown to be antiviral, antibiotic and anti-tumour. The aim of this study was to determine the biological activity of four cyclic dipeptides synthesized in this laboratory: cyclo(L-phenylalanyl-L-prolyl), cyclo(L-tyrosyl-L-prolyl), cyclo(L-tryptophanyl-L-prolyl) and cyclo(L-tryptophanyl-L-tryptophanyl). The enhancement or inhibition of calcium channels in ventricular myocytes from rats and delayed-rectifier potassium channels in ventricular myocytes from guinea-pigs were determined by use of the whole-cell patch-clamp technique. The induction of differentiation in HT-29 cells was assessed by assaying for an increase in the expression of alkaline phosphatase. Antibiotic properties against Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, Bacillus subtilus and Streptococcus sp. were determined by use of the Kirby-Bauer disc-diffusion assay. Results from these assays indicate that the cyclic dipeptides have biological activity in both prokaryotes and eukaryotes. Three of the dipeptides block cation channels in ventricular myocytes and all increase the expression of alkaline phosphatase. All the dipeptides have concentration-dependent antibacterial properties. These results suggest that with increased solubility the cyclic dipeptides might have potential as muscle relaxants, anti-tumour compounds and antibiotics.

Purification and partial characterization of a 'short' insectotoxin-like peptide from the venom of the scorpion Parabuthus schlechteri.

A disulfide-rich, low-molecular-mass toxin-like peptide has been isolated from Parabuthus schlechteri venom using gel filtration, ion exchange, and reversed phase chromatography. Partial characterization of this peptide reveals a relationship with four-disulfide bridge proteins belonging to the family of 'short' insectotoxins (44% residue identity). In recognition hereof, the peptide was named PBITx1 (sITx10). Our work also reports on the deduced sequences of two other 'short' insectotoxins from Buthus eupeus, I3 and I4, and it provides a consensus sequence and nomenclature for all known 'short' insectotoxins. Finally, sequence similarities with K+ channel blockers (charybdotoxin, kappa-conotoxin), and a Cl- channel blocker (chlorotoxin) are highlighted.

Development and optimization of a purification strategy for the venom of the scorpion Parabuthus transvaalicus.

In search for the toxic components constituting the venom of the southern African scorpion Parabuthus transvaalicus we compared and optimized several chromatographic separation protocols resulting in an efficient venom purification strategy. We found that the sequential combination of gelfiltration (Superdex) together with reversed phase chromatography (C2/C18)-but not cation exchange (Mono S)-stood surety for the best purification.

Neurospecificity of phyto-bufadienolides is not related to differences in Na+/K+ pump inhibition.

The aim of the present study was to investigate the effects of neuro- (cumulative) and cardiotoxic (non-cumulative) bufadienolides originating from plants (phyto-bufadienolides) on the Na+/K+ pump current (Ip) in cardiac (rat and guinea pig) and dorsal root ganglion cells (guinea pig), and on Ca2+ currents in cardiomyocytes (guinea pig). All bufadienolides tested (non-cumulative drugs: thesiuside, tyledoside C; lanceotoxin B and tyledoside F for the neurotoxic group) were potent blockers of Ip at concentrations in the micro- and submicromolar range. K0.5 values for Ip inhibition in dorsal root ganglion neurones were slightly lower compared to cardiomyocytes, but the order of potency was similar in both cell types. Both classes of bufadienolides were equipotent in suppressing Ip, generated by high- and low-affinity pump isoforms. Phenomena related to pump inhibition, as hypercontracture and increase in T-type Ca2+ current in cardiomyocytes, were influenced to the same extent. Therefore, from these results, neurospecificity of some bufadienolides could not be explained by differences in Na+/K+ pump affinity.

The haemodynamic correlations of the cardiopulmonary flow index, a relatively non-invasive technique for diagnosis of myocardial pump insufficiency.

The cardiopulmonary flow index (CPFI) is the ratio of cardiopulmonary blood volume to stroke volume. OBJECTIVE. To compare the CPFI derived from a first-pass radiocardiogram and electrocardiogram with the usual haemodynamic measurements obtained by bedside catheterisation. DESIGN. Sixty-one patients in a coronary care unit who had flow-directed pulmonary artery catheterisation for clinical indications had a CPFI recorded together with the usual haemodynamic measurements and calculations. RESULTS. In patients with myocardial pump failure without significant pulmonary disease, linear regression analysis indicated that the best fit for the CPFI could be obtained with a model that used the inverse of stroke index and pulmonary capillary wedge pressure as independent variables. Ninety-six per cent of the variation in CPFI can be explained by variations in pulmonary capillary wedge pressure and stroke index. The CPFI correlated less well with these variables in patients with concomitant lung disease. CONCLUSION. The CPFI is a potentially useful and relatively non-invasive index of haemodynamic function in acutely ill patients without significant pulmonary disease.

In vivo effects of a novel calcium antagonist (R56865) against induced epoxyscillirosidin and tulp poisoning in sheep.

Two anaesthetized sheep were intoxicated with epoxyscillirosidin, the main cardio-active bufadienolide, extracted from Homeria pallida (Natal yellow tulp). The epoxyscillirosidin was injected intravenously as a bolus of 50 micrograms/kg, followed 30 min later by a continuous infusion in a normal saline drip (0.9% NaCl) at 25 micrograms/kg/h. In addition, another two conscious sheep were poisoned by intraruminal dosing of 1,25 g/kg of dried H. pallida plant material. Electrocardiograms, heart and respiratory rates and venous-acid-base levels were recorded prior to and at approximately 30-60 min intervals during the course of the experiment. Additional recordings were made when animals showed signs of intoxication. R56865 (Janssen Pharmaceutica, Pty Ltd), a novel Ca++ antagonist, was administered at the first distinct signs of cardiac disturbances in the sheep given epoxyscillirosidin and after development of tachycardia and dyspnoea in those that received plant material. Activated charcoal was drenched at 3 g/kg to both sheep that received H. pallida about 1 h after the initial administration of R56865. All H. pallida sheep and one of the epoxyscillirosidin sheep survived. The signs of intoxication with H. pallida, namely groaning and tachypnoea, abated within minutes of treatment with R56865, but returned c. 30 min later in both animals. The treatment apparently had little effect on heart rate and EKG changes. One of the epoxyscillirosidin sheep was treated while exhibiting paroxysmal ventricular tachycardia. Although a transient improvement in conduction disturbance was recorded, the animal died soon afterwards. The results of this study indicate that the in vivo response of R56865 against induced bufadienolide cardiac disturbance in sheep is not as evident as that observed with R56865 against similar cardiac disturbance in vitro. The potential use of R56865 together with activated charcoal is discussed.

Fetal bilateral obstructive uropathy: a series of nine cases.

Bilateral obstructive uropathy is increasingly diagnosed in early pregnancy by ultrasound examination. Termination of pregnancy presented an opportunity to study uropathy in nine cases between 18 and 24 weeks of gestation. En bloc dissection of the urinary tract and subserial sectioning of the urethra revealed obstruction at the level of the membraneous urethra in all cases. No structural obstruction could be demonstrated in three cases, and urethral valves caused partial obstruction in two cases. The urethra was distorted by a fibrous band in one case. In three cases overriding urethral lumens appeared to represent incomplete or faulty canalization at the angled junction of the developing posterior and anterior urethra. Urethral obstruction is considered the major etiologic factor in the development of bilateral fetal uropathy and presumably the prune-belly phenotype.

Progressive familial heart block type I. Clinical and pathological observations.

Progressive familial heart block type I (PFHB-I) is an autosomal inherited disease. It was previously postulated that the disease is limited to the cardiac conduction tissue. The presentation of a patient with dilated cardiomyopathy focused on the possibility that this might be part of PFHB-I. This observation led to routine echocardiographic examination of patients with complete heart block, who belonged to PFHB-I families, and another 5 cases with signs of dilated cardiomyopathy were identified. This is the first time, to our knowledge, that the histological picture of PFHB-I has been described. From these case reports it is clear that in the presence of a dilated cardiomyopathy the prognosis in PFHB-I tends to be poor.

The toxic effects on cardiac myocytes of tyledoside F, a cumulative neurotoxic cardiac glycoside isolated from Tylecodon grandiflorus.

To investigate the cardiac cellular effects of tyledoside F, a cumulative neurotoxic bufadienolide and ouabain, a non-cumulative cardenolide, the whole-cell clamp method was used to measure the Na-K pump current after the Na-K pump had been activated by high intracellular Na2+. The toxic effects of tyledoside F and ouabain on cardiac myocytes were also investigated by observing the effect of the Ca2+ overload on the variability of myocytes during a period of 75 min. From the results it is clear that there are similarities in the direct effects of tyledoside F and ouabain on the Na-K pump. It was found that ouabain inhibited the Na-K pump current more than that of tyledoside F. With regard to Ca2+ overload, there are differences in their mode of production of Ca2+ overload because cinnarizine protects the myocytes against ouabain-induced Ca2+ overload but not against tyledoside-induced Ca2+ overload. This study shows that with the whole-cell clamp technique tyledoside F inhibited the Na-K pump in a manner similar to inhibition of the pump by ouabain. Viability studies with myocytes indicated that tyledoside F also has other effects which are different from these of ouabain.

A comparison of haemodynamic and vasoconstrictory responses in sheep with a toxic fraction from Pachystigma pygmaeum and with the plant material.

ST-segment changes in the ECG, which are an indication of acute myocardial ischaemia, are obtained when a small quantity of an extract from dried Pachystigma pygmaeum is injected intravenously in sheep. When the fraction was injected subcutaneously, animals reached a crisis after about 5 h, with low values of stroke volumes and high values for pulmonary arterial pressures, pulmonary vascular resistances and heart rates. The haemodynamic changes are an indication of the development of pump failure of the heart. In sheep, injected subcutaneously with the toxic fraction, as well as for sheep dosed with plant material through rumen fistula, increased serum levels for thromboxane and increased or decreased levels for prostacycline were observed. The experimental results are interpreted as being an indication that these prostaglandines may be involved in the development of gousiekte by impeding cardiopulmonary function as a result of coronary and pulmonary vasoconstriction. The sudden death observed in some gousiekte sheep may be due to myocardial ischaemia and associated arrhythmias.

Lafora-body disease with optic atrophy, macular degeneration and cardiac failure.

A 17-year-old boy was admitted to hospital in acute cardiac failure and psychosis. The clinical course, EEG records and tissue diagnosis, including biopsies of brain, skin, skeletal muscle, peripheral nerve and liver were compatible with Lafora-body disease (LBD). Unusual features were those of optic atrophy and macular degeneration, signs generally regarded as negative criteria for the diagnosis of this disease. We also present the findings on endomyocardial biopsy which was performed because cardiac failure as an early symptom of LBD has not been previously described. The patient died in status epilepticus a few months after discharge from hospital.

The regulation of the ratio of the cardiopulmonary blood volume to stroke volume in sheep.

Volume expansion with dextran was used in unanaesthetised sheep to investigate the mechanisms which are responsible for keeping the ratio of the cardiopulmonary blood volume to stroke volume (CPFI) constant under physiological conditions. For animals with heart rates lower than 80, active pulmonary vasoconstriction was mainly responsible for the regulation obtained with volume expansion, while the Starling mechanism was responsible for keeping the ratio constant for animals with heart rates above 79. The involvement of a regulatory mechanism was shown by the absence of large changes in the CPFI after inducing mechanical stress on the cardiopulmonary system as a result of experimental hypertension. Results obtained with receptor blockade showed that active pulmonary vasoconstriction may be the result of a reflex mechanism with parasympathetic efferents. It is suggested that the receptors for this reflex are situated in the pulmonary arteries and are activated by the pressure changes as a result of heart contractions.

Systemic lupus erythematosus with coronary vasculitis and massive myocardial infarction. A case report.

A 32-year-old white woman presented with angina pectoris and an acute myocardial infarction (MI) complicated by congestive cardiac failure. Other symptoms and results of immunological investigation were highly suggestive of systemic lupus erythematosus (SLE). Thallium-201 scintigraphy confirmed an extensive MI, as initially suspected from an ECG. Cardiac catheterization delineated a poorly contracting left ventricle secondary to MI. Selective coronary angiography showed features suspicious of coronary arteritis involving the left anterior descending and left circumflex coronary arteries. Right ventricular endomyocardial biopsy failed to show any 'small-vessel disease', vasculitis or myocarditis. We suggest that the acute MI was caused by coronary arteritis due to SLE. Overview of the literature indicates that coronary arteritis is not as rare a complication of SLE as previously believed; however, acute MI is most unusual.

Hypertrophic obstructive cardiomyopathy with pseudo-myocardial infarction pattern. A case report.

A 60-year-old woman with mild hypertension and presumed ischaemic heart disease was followed up over a very long period on account of angina pectoris. Acute myocardial infarction (MI) was suspected on the basis of the history, ECG findings and serum enzyme values, but disproved by radioisotope investigation. Echocardiography demonstrated features of hypertrophic obstructive cardiomyopathy (HOCM), a diagnosis supported by cardiac catheterization and endomyocardial biopsy (EMB). Histological features of HOCM were absent from left ventricular EMB specimens despite a significant intraventricular gradient, but the right ventricular EMB demonstrated extensive changes of HOCM despite a small intraventricular gradient. Cardiac catheterization excluded previous MI and coronary artery disease. A further interesting feature was the development of congestive cardiac failure, which necessitated modification of her drug therapy).

Unstable angina pectoris secondary to multiple calcified coronary artery masses. Successful treatment with coronary artery bypass surgery.

A 31-year-old doctor's wife suffered from severe unstable angina pectoris (AP) due to two large, heavily calcified masses involving the right coronary artery and the left anterior descending branch of the left coronary artery. The causes of the masses could not be determined with certainty, but in view of the history (which included the ingestion of large quantities of raw boerewors (traditional spiced sausage) and histopathological findings, we believe that they were coronary artery aneurysms which developed secondary to coronary arteritis many years previously. The possibility of echinococcal (hydatid) infection is also discussed. Cardiac surgery entailed total excision of both masses, together with sections of their accompanying coronary arteries which had become fibrotic as a result of the arteritis, and reestablishment of coronary blood flow by the insertion of two saphenous vein coronary artery bypass grafts. Her AP was dramatically relieved and she continues to be asymptomatic without taking anti-anginal drugs.