Potassium balance in piretanide and digoxin treatment.

Piretanide, a new potent diuretic, was given to 18 healthy male subjects to determine its effect on serum, total body (TBK), and red cell potassium (RCP). TBK and RCP were measured before treatment to establish baseline values, after which all subjects received 6 mg piretanide a day for 14 days. After this period subjects were divided into two groups; group 1 received 6 mg/day piretanide for 14 more days and group 2 received the same dose of piretanide with 0.5 mg digoxin daily during the remaining 14 days. All treatments were terminated after 28 days, but subjects remained under observation for another 14 days. Serum potassium, TBK, and RCP were measured weekly during the 42-day period. Piretanide in a dose of 6 mg daily for a period of 6 wk did not induce a fall in serum potassium, TBK, or RCP. The addition of digoxin for 2 wk after piretanide alone for 2 wk did not decrease serum potassium and TBK, but RCP fell under the influence of piretanide with digoxin.

Kinetics, distribution, and sites of destruction of canine blood platelets with In-111 oxine.

In five normal dogs we have studied the survival, tissue distribution, and fate of autologous platelets labeled with indium- 111 oxine. The methods include blood sampling, computer-assisted scintigraphy, and whole-body profile scanning. Mean In- 111-platelet recovery in the circulation was 45 +/- 22.5 (s.d.) and survival 124.6 +/- 10.5 hr. Platelet survival curves fitted a linear function best. Initially platelets pooled rapidly in the spleen with a single exponential function, and at zero-time equilibrium (35 +/- 4)% of the injected In- 111 was located in this organ. Early hepatic uptake was also significant, and constituted (20 +/- 4)% of total-body radioactivity. As labeled platelets disappeared from the circulation, In- 111 activity in the spleen increased progressively and linearly to reach (59 +/- 9)% of the body activity at 120 hr. Hepatic radioactivity decreased with time but to a lesser extent than that of the heart. The results indicate that in the dog the major site of destruction of platelets is the spleen, with the liver playing a less important role.

Kinetics and in vivo redistribution of (111)Indium-labelled human platelets after intravenous protamine sulphate.

The pathogenesis of thrombocytopenia induced by intravenous protamine sulphate was studied in six patients who underwent cardiopulmonary bypass surgery, and in three normal volunteers. Autologous platelets were labelled with (111)Indium-oxine. Platelet lifespan was determined. In vivo (111)In-platelet localization, organ redistribution and sites of destruction were quantitated with a scintillation camera and a computer-assisted imaging system. Protamine induced a transient thrombocytopenia, maximal 5-10 min after injection, and 30-40 min in duration. . The thrombocytopenia was accompanied by a transient accumulation of platelets in the liver. The splenic platelet pool remained unaltered and no platelets accumulated in the lungs. Platelet survival, measured in two volunteers, was slightly longer than normal and fitted a linear function best. There was a severe transient neutropenia during the period of thrombocytopenia. We conclude that protamine-induced thrombocytopenia is caused by hepatic accumulation of "activated" platelets or platelet aggregates, the process is reversible, and in the two normal volunteers studied, platelet survival was not affected.

Preparation of a viable population of indium-111-labelled human blood platelets.

Factors influencing labelling of human platelets with 111Indium-8-hydroxyquinoline ([111In]-oxine) in a physiological saline medium were investigated. The efficiency of labelling is influenced by time of incubation, concentration of oxine, and pH of the incubating medium. It was found that a viable platelet population could be labelled under the following conditions: (1) centrifugation of platelet rich plasma in polystyrene conical tubes at 800 g for 15 min; (2) resuspension of the platelet pellet in saline, pH 5.5; (3) incubating for 30 min at 22 degrees C with [111In]-oxine at a concentration of 6.25 mg oxine/litre platelet suspension; (4) washing once with platelet poor autologous plasma (PPP); and (5) finally resuspending the platelets in PPP. The labelled platelets aggregated normally with collagen and ADP. Electron microscopy, done immediately after labelling, showed internal organelle reorganization characteristic of activated platelets. These ultrastructural features were reversible on incubation in PPP at 37 degrees C for 30 min. The 111In is not released from aggregated platelets and the label does not elute from incubated platelets for at least five hr. We conclude that human platelets thus labelled are suitable for in vivo kinetic studies.

Kinetics and sites of sequestration of indium 111-labeled human platelets during cardiopulmonary bypass.

A new approach for the study of the kinetics and quantification of the in vivo and ex vivo sites of sequestration of platelets during cardiopulmonary bypass (CPB) is described. Autologous platelets of four patients were labeled with 111In-oxine and reinfused on the day prior to CPB for coronary artery bypass grafting. Changes in blood 111In-labeled platelet radioactivity and blood platelet counts were monitored during the operation. In vivo 111In-labeled platelet redistribution was quantified with a scintillation camera and a computer-assisted imaging system before and after CPB. Sequestration of 111In-labeled platelets in the bubble oxygenator was measured. 111In-labeled platelet activity in the blood decreased by 46% +/- 5% within 5 minutes of CPB, but this decrease was mostly due to hemodilution; the true loss of platelets from the circulation was 13% +/- 4%. Intraoperatively, whole body 111In activity decreased by oxygenator 10.8% +/- 1.3% of administered platelets were sequestered, especially in the innermost active layers of the defoaming mesh of the bubble oxygenator. Mean survival time of circulating platelets was 58 +/- 8 hours and fitted an exponential function best. The bleeding time increased to 40 minutes during operation and returned to normal within 24 hours. During operation 111In-labeled platelets accumulated somewhat in the liver (10.7%) but not in the spleen, thorax, or head. In the 48 hours after operation, platelets were sequestered mainly in the liver. The scintillation camera with computer-assisted imaging allows in vivo quantitative studies of platelet kinetics of a type which has not been possible with previous techniques.

Evidence of direct positive inotropic and chronotropic actions by PGE1 not mediated by cyclic AMP in conscious sheep.

The underlying mechanism for the cardiac responses to PGE1 has not yet been fully elucidated. In order to investigate a possible role for cyclic AMP in the positive inotropic and chronotropic actions of prostaglandin E1 (PGE1) in conscious sheep, theophylline-ethylenediamine was used to inhibit phosphodiesterase activity. Any significant potentiation or the lack of potentiation of the measured cardiac response to PGE1 was then used as a criterion to establish whether the cardiac actions of PGE1 were produced by an alteration in the intracellular levels of cyclic AMP. The results suggest that PGE1 produced positive inotropic and chronotropic actions in conscious sheep, which is neither caused by the autonomic nervous system (baroreflexes) nor by changes in intracellular cyclic AMP levels. Further research seems warranted to establish whether a relationship exists between Ca2+ and the contractile response of PGE1. Such a relationship could then possibly explain the positive inotropic action of PGE1 in conscious sheep.

Radiation dose from human platelets labelled with indium 111.

The biological distribution of 111In-labelled platelets in normal subjects was determined by whole-body counting and scintillation-camera computer-assisted imaging. Using these data, organ radiation dose was quantitated. The highest radiation dose of 7.4 mGy/MBq (27.4 rad/mCi) was received by the spleen and 0.97 mGy/MBq (3.6 rad/mCi) by the liver. While body radiation dose was 0.25 mGy/MBq (0.9 rad/mCi). The gonad radiation dose of males was 0.14 mGy/MBq (0.5 rad/mCi) and that of females 0.22 mGy/MBq (0.8 rad/mCi). These estimates indicate that radiation doses received from 8.6 MBq of 111In-labelled platelets are well within acceptable limits, and that 111In is a safe labelling agent for the study of platelet kinetics.

Aspects of folate metabolism in lactating women studied after ingestion of 14C-methylfolate.

Radioactive methylfolate (14C-5CH3H4PteGlu) (10-14 microgram/kg) was fed to four lactating women presenting with breast abscesses necessitating cessation of lactation. The appearance of radiofolate in milk, plasma and urine over the next 24 hours was investigated. In spite of a minimal postabsorption rise of plasma biofolate, plasma radiofolate (including a dialysis-resistant (bound) fraction) increased steadily to 1.26 to 5.11 microgram/l at 24 hours. Urinary radiofolate excretion was considerable. Total milk biofolate rose significantly by 15 to 28 microgram/l, in contrast with a much smaller radiofolate fraction (1.95-3.88 microgram/l) which at 24 hours was comparable with that of plasma. Milk radiofolate included a dialysis-resistant fraction rising to 0.75 to 1.15 microgram/l at 24 hours. On chromatography (Sephadex-DEAE-A50) plasma, urine and milk showed a nonbound radiofolate peak suggestive of 10-CHO.H4PteGlu. This folate may originate predominantly from the apocrine mammary glands. The in vitro labelled radiofolate milk binder could not be identified chromatographically, but it was shown that the in vitro milk binders of PteGlu and 5CH3H4PteGlu could be separated chromatographically.

Evaluation of different formulae for the study of platelet survival.

The International Committee of Standardization in Haematology has recommended in 1977 three methods for calculating the mean platelet survival time of isotope labelled platelets, although in recent years other mathematical equations were also suggested for the determination of platelet survival times. Seven different methods of calculating the mean survival time for normals were investigated and were compared with one another.

Comparison between the unsaturated plasma folate binder and in vivo labelled plasma folate binder.

Endogenous plasma folate binder denuded of folate by dialysis at pH 3, subsequently bound more methylfolate than folic acid, in contrast with the minor unsaturated plasma binder which bound folic acid in preference to methylfolate. On Sephadex DEAE-A50 chromatography 14C-CH3H4PteGlu bound to acid-denuded endogenous binder, eluted like the endogenous binder-radioactivity, labelled in vivo after oral 14C-CH3H4PteGlu. It is suggested that the endogenous plasma folate binder is not identical with the unsaturated binder.

Folate metabolism and in vivo radiofolate binding in normal, folate-deficient and folate-saturated subjects.

After ingestion of 14C-CH3H4Pte Glu by folate-deficient and folate-saturated subjects, and 14C-CH3H4PteGlu as well as 3H-PteGlu by a normal control subject, the dialysis-resistant (bound) plasma radiofolate fraction appeared increased in folate saturation and decreased in folate deficiency (compared with normal folate status). This suggests that absorbed radiofolate does not admix with the total folate pool before complexing with the plasma binder. As the bound plasma fractions appeared later than did the total biofolate peaks, in vivo plasma folate binding probably occurs independently of the intestinal folate absorption process. It also appears unrelated to postabsorption storage folate displacement, as this biofolate fraction is unbound. A bound radiofolate fraction persisting in plasma for 72 hours in spite of a normal food intake indicates a relatively inert binder complex.

Self-medication in a developing community.

Representatives of 600 households in Ga-Rankuwa were interviewed to ascertain which medicines they had in their homes and how they would treat themselves for common complaints. There was an average of 1,6 medicines in each household; of these, 89,2% were Western medicines and 9,4% traditional African medicines, while 1,4% could not be classified into either group. The majority of medicines had been obtained from pharmacies (37,1%), general dealers (34.9%) and hospitals or clinics (15,8%). Traditional sources (6,7%), private practitioners (2,4%) and other sources (3,1%) accounted for the rest. For the treatment of most common symptoms respondents preferred to use Western medicines, but on the whole they were reluctant to take them for diarrhoea and vomiting. Most traditional African medicines appeared to be used for coughs and colds.

In vivo plasma and urine folate binding after ingestation of 3H-folic acid and 14C-methyl-folate.

After simultaneous ingestion of equivalent amounts of [3H]folic acid (3H-PteGlu) and [14C]N5-methyl-tetrahydrofolic acid (14C-CH3-H4PteGlu) we were able to demonstrate progressive macromolecular binding of radiofolate in plasma, which appeared to be near maximal at 6 h. Bound radiofolate was predominantly of 14C-CH3H4PteGlu origin, and only at 24 h could 3H incorporation be demonstrated. The binder eluted with albumin from Sephadex DEAE-A50 columns. In urine a smaller bound radiofolate fraction, with approximately equal amounts of 3H and 14C, appeared after 5.5 h. Plasma chromatography showed radio-PteGlu (peak 1) to be rapidly converted to CH3-H4PteGlu (peak 2), with subsequent appearance of two further radiofolate peaks (peaks 3 and 4) the nature of which is as yet unclear. Urine showed similarly placed fractions but their magnitude differed, and urinary peak 3 in particular was much more prominent than its plasma counterpart.

Aspects of radiofolate absorption, metabolism and plasma binding.

After 14C-methyl folate (14C-MeTHF) was taken by mouth, progressive incorporation of this istope into the dialysis-resistant plasma folate fraction occurred. At 6 hours 68,9% of the total plasma radioactive folate was dialysis-resistant. We have previously shown that 14C-folic acid (14C-PGA) taken by mouth is not similarly bound at 6 hours. Chromatography of plasma on DEA A50 after 14C-PGA absorption, showed that PGA in plasma (peak 1) was gradually converted to MeTHF (peak 2) and the absence of bound radiofolate 6 hours after 14C-PGA ingestion probably reflects this conversion phase. No radiofolate appeared in red cells up to 11 days after isotope ingestion. Initial divergence between plasma biofolate and radiofolate indicated that 'cold' storage folate was being displaced by abosrbed radiofolate. Urinary radiofolate resolved into 3 fractions (peaks 2, 3 and4) on DEAE A50 chromatography. One of these (peak 2) corresponded to MeTHF, but PGA (peak 1) was absent. Plasma showed peaks 1, 2 and 3, but at 3 hours no equivalent of urinary peak 4 was evident. Further studies are indicated to characterise fractions 3 and 4.

A conjugate counting method to determine [75Se]SeHCAT retention in the human body.

To evaluate the functional integrity of the distal part of the ileum the retention of a gamma-labelled bile acid (SeHCAT) in the human body can be measured with a detector. Due to the lack of a whole body counter at our institution a two detector system was designed to measure SeHCAT retention and an evaluation of such a system has been made. The detectors are positioned on either side of a patient lying supine on a hospital trolley. The trolley is stepped forward in 100 mm steps, to determine the SeHCAT activity in the patient. With these counts the location of the SeHCAT activity and total activity present in the body can be determined. A water filled phantom and a phantom consisting of nine 1-L saline bags with 75Se activity placed in them was used to determine system performance. Four patients with no history of bowel disease were compared with published data for normals. Results showed that the system performed satisfactorily, and accurate quantitative measurements could be made, showing that this inexpensive system could be used where a whole body counter is not available.

Use of indium-111-labelled platelets in black stroke patients. A pilot study.

Human blood platelets labelled with indium-111 oxine have been shown to accumulate on damaged vascular surfaces and abnormal platelet deposition has been demonstrated in the carotid arteries of white stroke patients. Gamma scintigraphy of the carotid and cerebral arteries of 5 black stroke patients and 5 age- and sex-matched controls using 111In-labelled platelets showed no abnormal accumulation indicative of carotid artery disease.

In vitro binding of folates by body fluids.

It is useful to differentiate between saturated folate binders in serum (carrying endogenous folate) and unsaturated binders (investigated in the present study). These two groups of binders need not necessarily be chemically identical and the unsaturated binder may even be an in vitro artifact, especially when measured with non-physiological folates. Macromolecular binding of radio-active N-5-methyl tetrahydrofolic acid (CH3H4PteGlu) and/or folic acid (PteGlu) by human serum and urine was assessed by means of exhaustive saline dialysis, haemoglobin-coated charcoal adsorption, column chromatography with DEAE-Sephadex A-50, and sucrose gradient analysis. Binding was found to be minimal or absent. Charcoal adsorption showed a mean serum binding capacity of 0 mug/1. for PteGlu and 0.58 mug/1. for CH3H4PteGlu. In pregnancy the mean serum values were 0.23 mug/1. for PteGlu, 0.66 mjg/1. for CH3H4PteGlu, and with folate deficiency 0.30 mug/1. for PteGlu, 0.49 mug/1. for CH3H4PteGlu. Mean urinary folate binding was minimal (less than 0.5 mug/1.), and red cell haemolysate similarly revealed very low binding on exhaustive dialysis. Column chromatography showed that tracer doses of [14C]PteGlu added to serum migrated distally to the protein zone; [14C]CH3H4PteGlu similarly showed no evidence of protein binding. On a sucrose gradient [14C]PteGlu also separated clear of the protein zone.

Digoxin, whole body potassium and the electrocardiogram.

Previous studies have shown a significant linear relationship between the PTQ-index (a combination function of the PR-interval, corrected QT-time and T-wave depression in the ECG) and serum digoxin level in chronically treated patients. The relationship was confirmed in the present study and it was shown that it could be changed by concomitant administration of potassium chloride or furosemide, and that there was marked interindividual variation in response. An inverse linear relationship between PTQ-index and whole body potassium was found during chronic administration of a constant daily dose of digoxin, but no such relationship was found for serum potassium.

Kinetics, distribution and sites of destruction of 111indium-labelled human platelets.

The survival, tissue distribution and fate of 111In-oxine labelled autologous platelets in six normal humans were studied with serial blood sampling, scintillation camera and computer-assisted imaging, whole body profile scanning, and rectilinear scanning. 111In-platelets recovery in the circulation was 72+/-16% and survival was 216+/-17 h. Platelet survival curves fitted a linear function best. Initially platelets pooled rapidly in the spleen as a single exponential function, and at 90 min 26% of the injected 111In was located in this organ. Early hepatic uptake was also significant and at 90 min constituted 16% of total body 111In-activity. As labelled platelets disappeared from the circulation there was a threefold increase of radioactivity in the liver to reach 39% of whole body activity at 216 h. Radioactivity also increased significantly in the spleen (33.3% at 216 h). There was significant residual radioactivity in the thoracic and lower abdominal regions at 216 h, suggesting that platelets are also sequestered in the bone marrow. Radioactivity in the lower limbs almost disappeared with time (0.7% at 216 h), indicating that utilization of platelets in the peripheral vasculature is not marked in normal subjects.