Modification of human platelet response to sodium arachidonate by membrane modulation

Previous studies have shown that the majority of mongrel dogs have platelets that do not aggregate when stirred with sodium arachidonate, but respond normally to other aggregating agents. Here we have created a model in which human platelets mimic the unusual behavior of canine cells. Brief exposure of human platelets to low concentrations of prostacyclin will convert them to a physiologic state resembling that of canine platelets without causing elevation of intracellular levels of cAMP. Studies on the conversion of arachidonic acid showed that prostacyclin did not cause any inhibition of thromboxane B2 generation. Exposure of prostacyclin treated platelets to epinephrine restored their sensitivity to arachidonate without causing any detectable changes in levels of cAMP. The selective inhibition achieved by PGI2 could be mimicked by the endoperoxide analog. U44069, a thromboxane inhibitor, U-51605, and an endoperoxide/thromboxane receptor blocker, 13-APA. Inhibition induced by these compounds was also reversed by epinephrine. A calcium channel blocker, verapamil, and an alpha blocker, dihydroergocryptine, effectively blocked the corrective influence of epinephrine on prostacyclin-treated platelets. Results of these studies show that catecholamines and prostaglandin receptors share close sites on the membrane and exhibit a degree of cooperativity in calcium modulation. Dog platelets that do not respond to products of AA metabolism and the human platelets made to behave like canine platelets may have a defect in calcium mobilization and this defect is corrected by adrenaline through an alpha receptor modulation.

Influence of trifluoperazine on platelet aggregation and disaggregation

Calmodulin has been shown to activate platelet phospholipase A2 and initiate the metabolism of arachidonic acid. Trifluoperazine (stelazine), an agent which selectively binds calmodulin, inhibits phospholipase activity induced by calcium. We have evaluated the effect of this agent on the aggregation, disaggregation and reaggregation of human platelets. Results of our study have shown that stelazine is a selective inhibitor of the second wave response of platelets to the stimulation of agonists. The compound causes dissociation of aggregated platelet clumps and induces a refractory state in dispersed cells. Epinephrine reverses the refractory state and potentiates the response of dissociated cells to the action of thrombin, arachidonate and ionophore A23187. Stelazine elevates cAMP levels to some extent and inhibits release of labeled arachidonic acid from platelet membranes in response to thrombin induced stimulation. Epinephrine may correct stelazine induced inhibition by acting through alpha-adrenergic mechanism, by inducing changes in membrane permeability to calcium, by releasing membrane associated calcium or by directly promoting deacylation of phospholipids.

The influence of epinephrine on prostacyclin (PGI2) induced dissociation of ADP aggregated plateletes

Prostacyclin (PGI2) is a powerful inhibitor of platelet function and recent studies have indicated that it can dissociate aggregated platelets in vivo. The present investigation has evaluated the mechanism involved in the dissociation of ADP aggregated platelets by PGI2, the influence of epinephrine on the process of PGI2 mediated disaggregation, and effects of the catecholamine on the refractory state of PGI2 dispersed cells. Dissociation of ADP aggregates by PGI2 was concentration and time dependent, caused complete disappearance of sensitive platelet clumps and restored platelet discoid form. The dispersed platelets were refractory to further stimulation by ADP, thrombin, arachidonate or the calcium ionophore, A23187. Measurement of cAMP revealed no change in control levels after aggregation by ADP, but a sharp increase during and after dissociation by PGI2. Epinephrine added to ADP aggregates before or after PGI2 blocked disaggregation, or stopped dissociation if already in progress, and caused a rapid fall in the high levels of cAMP stimulated by PGI2. Agents to which PGI2 dissociated platelets were refractory, including ADP, arachidonate and A23187 caused no lowering of elevated cAMP levels. Reduction of high levels of cAMP in PGI2 dispersed platelets by epinephrine did not result in reaggregation. However, epinephrine addition to refractory platelets restored in large measure their sensitivity to aggregation by arachidonate, thrombin, ADP and A23187.

Influence of pH on the prostacyclin (PGI2) mediated inhibition of platelet function

Prostacyclin (PGI2) stimulates platelet adenylate cyclase, elevates intracellular levels of cyclic adenosine monophosphate and blocks the response to aggregating agents. It is rapidly hydrolyzed (T 1/2-5 min) to 6-keto prostaglandin F1 alpha at acid or neutral pH. As a result, platelets incubated with PGI2 will recover spontaneously and respond to aggregating agents within 15--60 min, depending on the initial PGI2 concentration. In the present study we have evaluated the influence of temperature and pH on the stability of PGI2 and its effects on platelet function. PGI1 in Tris buffer was stabilized at several pH levels and stored at 37 degrees C, 23 degrees C, and 4 degrees C. Inhibitory influence in platelet function was lost rapidly at pH 7.2--7.4, lasted several hours at pH 7.8 and was retained indefinitely at pH 7.8 and was retained indefinitely at pH 8 or above. PGI2 (2.8 nM) completely inhibited the response to arachidonic acid for 15 min. at pH 7.4, for at least 1 hour at pH 7.8 and showed no reversal of inhibition after 48 hours at pH 8. However, PGI2 inhibited samples at pH 8 completely recovered their sensitivity to arachidonic acid when the pH was reduced to 7.4. These findings indicate that the biological activity of PGI2, though labile at neutral pH, is stable at pH 8 and can inhibit, cAMP mediated platelet functions for at least 48 hours. Because of its pH dependence, PGI2 may be a useful agent for prolonging the sensitivity of stored platelets.

Long-term function of NCGT vascular conduits in a multicenter trial: evaluation of physical chemical parameters

Our experience with the NCGT graft has now encompassed 12 years in experimental animals and 4.5 years clinical experience with 134 grafts in man. It has previously been suggested that vessel wall structure, interface-charge, electric potential, and polarity of the blood intimal interface appear critical in the prevention of intravascular thrombosis in all vascular prosthetic bypass grafts. This concept has now been confirmed using ferritin, colloidal iron and fluorescamine intimal labelling. These provide a quantitative special characterization of the surface charges of several grafts, including the NCGT graft. Study indicates that each step in the production of the NCGT graft results in a cumulative increase in the structured negative charge of the vascular interface. The more dense the structured negative charge of the prosthesis, the more resistant is the graft to short and long-term thrombosis in experimental animals and man. The experience has been confirmed with a comparative analysis of implantation results in 105 patients up to 4.5 years with 65 to 70% patency rate over that time interval. Statistical analysis of parameters confirm again that the polarity and structure of the vascular interface is important in the effective function and patency rate of the grafts.

Bacterial flora in acute small bowel obstruction

The bacterial flora has been studied by direct sampling techniques at various levels in 25 cases of acute small bowel obstruction. The presence of coliform bacteria in the distal ileum below the level of obstruction and progressive increase of bacterial counts from the jejunum towards the distal ileum above the obstruction suggest that ingestion may not be the only factor of bacterial growth in the small bowel in acute intestinal obstruction. Moreover, indirect peritoneal contamination in 8 cases of long-standing acute small bowel obstruction indicates that possibly a combination of multiple factors like ingestion of food, retrograde spread from the large bowel, lymphatic and/or hematogenous spread are responsible for bacterial dissemination in and around the obstructed bowel.

Tranylcypromine induced hypertension is not mediated by the inhibition of prostacyclin synthesis

Tranylcypromine (TCP) is a monoamine oxidase inhibitor used extensively in the treatment of patients with reactive depression. Hypertensive crisis can complicate drug therapy, but the mechanism through which TCP causes high blood pressure is unknown. The present study was undertaken because recent investigations have shown that TCP can inhibit production of a potent vasodilator hormone, prostacyclin (PGI2), by blood vessels, possibly explaining the mechanism of pressor effects by the drug. Heart rate, left atrial, pulmonary artery and aortic pressures were monitored in dogs under control conditions and continuously following the IV infusion of TCP at the rate of 1 mg/kg over a period of one minute. Right femoral and the left internal mammary arteries were obtained during the control period and the left femoral and right internal mammary arteries resected between 6 and 30 minutes following drug infusion for PGI2 studies. Concentrations of the drug that caused significant elevation of the mean systemic pressure to 203 +/- 8 mmHg had no inhibitory effect on PGI2 production. Therefore, the influence of TCP on the hemodynamic parameters does not appear to be mediated through the inhibition of vascular PGI2 synthesis.

The prevalence of hypertension in the Indian population of Durban

In a random house-to-house study of 1 000 Indians the prevalence of essential hypertension according to the World Health Organization (WHO) criteria was 19% (females 22%; males 15%). The study revealed that the prevalence of hypertension was higher than in published data from India. Ethnicity in our study caused a significant variation in prevalence. Prevalence was lower than in our urban Zulu study. Blood pressure rose with age, but there was a greater rise in systolic than in diastolic blood pressure. Prevalence in males and females under 40 years were equal. There was an association between hypertension and diabetes mellitus. More effective screening and therapeutic programmes should be initiated in the Indian population because of the high prevalence of hypertension which may lead to complications if untreated, and because 58% of the hypertensive subjects were untreated or had discontinued therapy.

Acute toxicity of 12,13-epoxytrichothecenes in one-day-old broiler chicks

Acute toxic effects of several 12,13-epoxytrichothecenes were investigated in 1-day-old broiler chicks by single oral doses. The 7-day median lethal dose values of purified 8-acetylneosolaniol, diacetoxyscirpenol, T-2 toxin, HT-2 toxin, neosolaniol, deacetyl-HT-2 toxin, and T-2 tetraol were 3.22 +/- 0.26, 3.82 +/- 0.40, 4.97 +/- 0.44, 7.22 +/- 0.39, 24.87 +/- 2.64, 30.18 +/- 7.53 (incomplete value), and 33.79 +/- 5.39 mg/kg of body weight, respectively. Deaths occurred during the 8- to 60-h period after dosing with the tested trichothecenes. Within 4 to 10 h after dosing, inappetence, asthenia, diarrhea, and coma generally developed. Sublethal doses of each toxin decreased feed consumption and weight gain proportionally with the amounts of toxins administered. These results demonstrate that the toxic potency of 12,13-epoxytrichothecenes varies depending on the modification of side chains in the molecule.

Familial incidence of L-xylulosuria

During a survey for genetic disorders, L-Xylulosuria, an autosomal recessive condition, was found to affect three cousins in an inbred family. There were no clinical symptoms.

A sibship with hypervalinemia

During routine screening of amino-acid disorders, we detected hypervalinemia in two sibs (a girl of 4 and a boy of 3 years of age) of a consanguineous marriage. There was no excess accumulation or excretion of leucine or isoleucine, which presumably indicates the absence of valine transaminase.

Multiple fistulas between the coronary arteries and the left ventricle

The authors report a case of fistulas connecting the anterior descending, circumflex, and dominant right coronary arteries with the left ventricle. Although fistulous connections between a coronary artery and a cardiac chamber have been described before, this is only the third known case in which all of the coronary arteries communicated with the left ventricle.

Radionuclide venography of the lower extremities and inferior vena cava by continuous injection and moving bed gamma camera technique

Radionuclide venography has proved to be a tedious procedure because of the need for multiple imaging set-ups with coordinated, repeated injections of radionuclide. The use of a moving bed gamma camera has shortened the procedure. This method enables the entire sapheno-femoral-iliac-caval system to be visualized in continuity on a single film. The moving table top system also adequately imaged the suspected areas of thrombi or endothelial damage on the post-exercise study on a single film.

Oxygen toxicity: augmentation of antioxidant defense mechanisms in rat lung

In studies directed at determining the activities of selected enzymes in lung tissue after in vivo exposure to hyperoxia, 70-day-old rats were exposed to 85% or 90% O2 for 1-14 days. After 7 days of exposure to 90% O2 (1atm), superoxide dismutase activities in mitochondrial and cytosolic fractions increased, respectively, to 245 and 145% of control; glutathione peroxidase, glutathione reductase, and glucose-6-phosphate dehydrogenase activities increased, respectively, to 317, 175, and 413% of control. The levels of reduced glutathione and total nonprotein sulfhydryl compounds were elevated to 195% and 365% of control. Similar changes were observed in rats exposed to 85% O2 for up to 14 days, but to a lesser degree. The changes are interpreted as a reflection of the overall magnitude of oxidant-induced lung injury-reparative processes. The results suggest that hyperoxia induces an increase in lung "antioxidant" defense capabilities. This apparent adaptive response may be important in decreasing the susceptibility of lung tissue to continued O2 toxicity.