A comparison of the pharmacokinetics of metronidazole in man after oral administration of single doses of benzoylmetronidazole and metronidazole

1 Three healthy male volunteers were treated with benzoylmetronidazole suspension (3.2 g equivalent to 2 g metronidazole) in a pilot study to investigate the absorption of benzoylmetronidazole into the systemic circulation. A further ten healthy male volunteers took part in a crossover study to compare the pharmacokinetics of metronidazole and its principal oxidative metabolites after administration of benzoylmetronidazole (equivalent to 2 g or 400 mg of metronidazole) or metronidazole (400 mg).

2 The plasma pharmacokinetics of metronidazole and metabolite I[1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole] and plasma and urinary concentrations of these, plus benzoylmetronidazole and metabolite II [2-methyl-5-nitroimidazole-1-acetic acid], were determined using specific and sensitive high performance liquid chromatographic assay procedures.

3 No benzoylmetronidazole was observed in any plasma or urine sample assayed. The values for and times of the highest observed plasma metronidazole concentrations after a single oral dose of benzoylmetronidazole, equivalent to 2 g and 400 mg metronidazole, were 17 μg/ml at 5.1 h after dosing and 4.6 μg/ml at 3.2 h after dosing, respectively. Following oral administration of metronidazole (400 mg), the comparable values were 8.5 μg/ml at 0.8 h after dosing. Peak plasma concentrations of metabolite I after each dose were comparable with each other when corrected for the amount of metronidazole reaching the systemic circulation. The peak concentrations of this metabolite were markedly lower than the peak metronidazole concentrations in the same volunteer. Metabolite II was observed in low concentrations (0.8 μg/ml or less) in plasma at a few time intervals after administration of the higher dose of benzoylmetrinidazole and was not detected at any time interval after administration of benzoylmetronidazole (640 mg, equivalent to 400 mg metronidazole) or metronidazole (400 mg).

4 Pharmacokinetic parameters of metronidazole absorption are markedly different after administration of benzoylmetronidazole than after dosing with metronidazole, but the pharmacokinetic parameters of metronidazole and metabolite I elimination are essentially identical after equimolar doses of each form of the drug. The systemic availability of metronidazole derived from benzoylmetronidazole is approximately 80% of that from metronidazole and is independent of dose over the range studied.

5 The mean value for minimum plasma metronidazole concentration at steady-state during the o.d. administration of benzoylmetronidazole (3.2 g equivalent to 2 g metronidazole) was predicted (from these single dose data) to be 6.2 μg/ml. Thus, these predictions suggest that the majority of patients will maintain therapeutic plasma metronidazole concentrations for the whole of the dosing interval during a once-daily dosing regimen. This oral liquid formulation of metronidazole may thus be regarded as a suitable alternative to other presentations of the drug.

     

A new bioassay for glucagon

1 The relaxant action of glucagon has been studied in strips of rabbit renal arteries partially contracted by a low concentration (1 ng/ml) of noradrenaline.

2 The preparation was relaxed in a dose-dependent manner by concentrations of glucagon varying between 25 ng/ml and 420 ng/ml.

3 The relaxant effect of glucagon (0.1 μg/ml ED₆₀) on this preparation was not affected by propranolol (5.0 μg/ml), cimetidine (10 μg/ml), diphenhydramine (10 μg/ml), indomethacin (5.0 μg/ml), phentolamine (1.2 μg/ml), atropine (10 μg/ml) and 8-Leu-AT_II (1.0 μg/ml) but was slightly potentiated by Des-Arg⁹ Leu-OMe⁸-Bk (25 μg/ml) and indomethacin (50 μg/ml).

4 The dose-response curve to glucagon remained parallel in the presence of papaverine (2.5 μg/ml) but was shifted to the left by a factor of 2.5 to 2.8. Theophylline (250 μg/ml) also potentiated the vascular relaxation induced by glucagon.

5 Insulin (10 μg/ml) did not influence the relaxant effect of glucagon.

6 The removal of the N-terminal amino acid (His) of glucagon reduced by 89% the biological activity of this fragment on the vascular preparation. The removal of the C-terminal amino acids Met-27, Asn-28 and Thr-29 of glucagon resulted in a fragment which was inactive either as an agonist or as an antagonist when tested at concentrations as high as 925 ng/ml.

7 It is concluded that the relaxation of partially contracted strips of rabbit renal arteries by glucagon constitutes a simple, sensitive, relatively specific and reliable bioassay which may be useful for the determination of glucagon in biological materials and for structure-activity relationship studies with this hormone.

     

The haemoglobin-oxygen dissociation curve: In vivo and in vitro effects of five β-adrenoceptor antagonists and lignocaine

1 The effects of several β-adrenoceptor antagonists and lignocaine on blood oxyhaemoglobin dissociation curves have been studied in healthy non-smoking subjects.

2 The P_O2 at 50% saturation (P₅₀) did not significantly change after oral propranolol 80 mg (single dose, and following 2 weeks' administration of 80 mg twice daily), or following separate intravenous injection of propranolol (0.2 mg/kg), practolol (1 mg/kg), atenolol (0.2 mg/kg) and SL 75212 (0.15 and 0.6 mg/kg).

3 Increases in P₅₀ were found after the addition of propranolol 100 and 500 μg/ml, and lignocaine 5 μg/ml to whole blood, but incubation with propranolol at 1000 ng/ml or less, or sotalol 5 and 500 μg/ml and 5 mg/ml resulted in no significant change in P₅₀.

4 These results suggest that to increase P₅₀ with propranolol requires plasma propranolol concentrations far in excess of concentrations normally achieved, and that the therapeutic effect of propranolol in patients with ischaemic heart disease cannot be attributed to an increase in P₅₀.

     

Plasma concentrations and cardiotoxic effects of desipramine and protriptyline in the rat

1 Desipramine and protriptyline were administered to anaesthetized rats by two consecutive intravenous infusions in order to obtain a peak level (first infusion) followed by lower steady state concentrations (second infusion) (Wagner, 1974). Theoretical plasma level time courses were confirmed experimentally.

2 Desipramine and protriptyline were measured in atria and ventricles. Increasing infusion rates led to proportional increases in plasma and atrial concentrations. The tissue/medium ratio ranged from 57 to 21 for desipramine and from 43 to 11 for protriptyline according to the time of determination during infusions.

3 Heart rate changes, deviation of the electrical axis of the heart and prolongation of atrioventricular conduction were recorded at fixed times during infusion.

4 Positive chronotropic effects were noted at plasma concentrations ranging from 0.035 to 0.1 μg/ml for desipramine and from 0.04 to 1.2 μg/ml for protriptyline. At higher plasma concentrations the positive chronotropic effect decreased and bradycardia developed. Both drugs induced right rotation of the electrical axis of the heart. Threshold plasma levels giving 40° rotation were 1.35 μg/ml (desipramine) and 1.75 μg/ml (protriptyline). Atrioventricular conduction was prolonged at threshold plasma concentrations of 2.2 μg/ml for desipramine and 3.6 μg/ml for protriptyline.

5 Desipramine is more cardiotoxic than protriptyline. This difference is discussed in relation to the plasma and heart concentration of the two drugs.

     

Prostaglandin inactivation in guinea-pig lung and its inhibition

1 Several compounds were tested for their ability to inhibit prostaglandin metabolism in guinea-pig lungs.

2 In isolated perfused lungs polyphoretin phosphate (PPP) inhibited prostaglandin metabolism being active at concentrations greater than 100 ng/ml and having an ID₅₀ of 2.15 μg/ml against prostaglandin E₂ metabolism and 1.55 μg/ml against prostaglandin F_2α metabolism.

3 At these doses no antagonism of the actions of prostaglandins was seen.

4 Diphloretin phosphate (DPP) was more active on a weight for weight basis and inhibition of inactivation of prostaglandins was seen at concentrations greater than 10 ng/ml, the ID₅₀ being 0.54 μg/ml against both prostaglandins E₂ and F_2α.

5 At concentrations greater than 5 μg/ml DPP antagonized the actions of prostaglandin F_2α.

6 The sulphydryl-binders N-ethyl maleimide (NEM) and sodium p-chloromercuriphenyl sulphonate (PCMS) also inhibited prostaglandin inactivation by guinea-pig isolated lungs.

7 All four compounds inhibited prostaglandin metabolism by a crude enzyme preparation from guinea-pig lungs.

     

Dose-response relationships in tropicamide-induced mydriasis and cycloplegia

1 Mydriatic and cycloplegic effects of tropicamide in the normal and in the guanethidine-treated human eye have been recorded following prolonged exposure of the eye to drug solutions.

2 Marked effects and satisfactory dose-response relationships were observed at drug concentrations within the range 1.25-40 μg/ml, by comparison with concentrations of 5-10 mg/ml usually applied as eye-drops.

3 The findings are discussed in relation to drug concentrations which produce cholinergic antagonism in vitro.

     

Purine antagonists in the identification of adenosine-receptors in guinea-pig trachea and the role of purines in non-adrenergic inhibitory neurotransmission

1 To test the possibility that adenosine receptors exist within the trachea of the guinea-pig, an attempt has been made to identify a compound with adenosine antagonist activity in this tissue.

2 Quinidine, phentolamine, phenoxybenzamine, 2-2′-pyridylisatogen tosylate (PIT) and caffeine were tested for antagonism of spasmolytic responses to adenosine, adenosine 5′-triphosphate (ATP) and adenine on the guinea-pig isolated trachea.

3 Quinidine (10 and 25 μg/ml), phentolamine (10 and 30 μg/ml) and phenoxybenzamine (10 μg/ml) had little or no effect on response to adenosine, ATP and adenine. PIT (21 μg/ml) potentiated responses to adenosine, ATP and adenine by an unexplained mechanism.

4 Caffeine (25 μg/ml) partially relaxed the trachea and inhibited spasmolytic responses to both adenosine and ATP, but not to adenine, isoprenaline, aminophylline or prostaglandin E₂ (PGE₂).

5 A number of compounds related to caffeine (xanthine, hypoxanthine, theophylline and theobromine) were tested for adenosine antagonist activity. Xanthine (300 μg/ml) and hypoxanthine (300 μg/ml) did not relax the trachea or antagonize spasmolytic responses to adenosine. Both theophylline (10 μg/ml) and theobromine (30 μg/ml) partially relaxed the trachea; theophylline, but not theobromine, antagonized spasmolytic responses to adenosine.

6 pA₂ values for caffeine and theophylline as antagonists of adenosine were 4.3 and 4.7 respectively. However, the slopes of the Schild plot regressions were significantly less than 1.0 for both compounds.

7 Four compounds, adenine, AH 8883, M30966 and ICI 63197, which like caffeine and theophylline, have phosphodiesterase inhibitory activity were tested for adenosine antagonist activity in the trachea. Adenine and AH 8883 had no effect and M30966 and ICI 63197 caused significant potentiation.

8 The effects of caffeine and theophylline were also investigated on the non-adrenergic inhibitory response to nerve stimulation (NAIR). Both caffeine (100 μg/ml, n = 4) and theophylline (30 μg/ml, n = 4) enhanced the NAIR (20 Hz) while virtually abolishing matched responses to exogenous adenosine.

9 The results support the existence of adenosine receptors in the guinea-pig trachea.

     

The effects of three β-adrenoceptor blocking drugs on isolated preparations of skeletal and cardiac muscle

1 The effects of propranolol, oxprenolol and practolol on the isometric twitch responses to electrical stimulation of isolated diaphragm muscles from the rat and of isolated papillary muscles from the rabbit are described.

2 Depression of the twitch responses of the diaphragm muscle was produced by propranolol (20 μg/ml), by oxprenolol (100 μg/ml) and by practolol (500 μg/ml).

3 Depression of the twitch responses of the papillary muscles was produced by propranolol (20 μg/ml) by oxprenolol (100 μg/ml) and by practolol (200 μg/ml).

4 No increase of twitch tension was produced by oxprenolol or practolol on either tissue.

5 It is concluded that propranolol, oxprenolol and practolol produce negative inotropic actions on isolated cardiac muscle by a mechanism unrelated to blockade of β-adrenoceptors and which occurs at doses which are well in excess of those doses required to produce β-blockade.

     

Studies on the cardiovascular effects of pindolol in DOCA/saline hypertensive rats

1 A hypotensive response to orally administered pindolol in conscious normotensive and deoxycorticosterone acetate (DOCA)/saline hypertensive rats (DS-rats) is described. In DS-rats, pindolol (10-50 μg/kg) produced a dose-dependent fall in blood pressure and elevation of resting heart rate.

2 The hypotensive response and tachycardia produced by oral pindolol (50 μg/kg) in DS-rats were prevented by propranolol (5 mg/kg), suggesting that pindolol's effects are mediated by β-adrenoceptor stimulation.

3 After mecamylamine (10 mg/kg), oral pindolol (50 μg/kg) produced a further fall in blood pressure in DS-rats, suggesting that its hypotensive effects are probably mediated in the peripheral vasculature.

4 Pretreatment with oral pindolol (10 or 50 μg/kg) resulted in a reduction of neuronally-induced tachycardia in pithed DS-rats; neuronally-evoked pressor effects were also antagonized by pindolol (50 μg/kg, orally).

5 Whereas pindolol, 50 μg/kg orally or intraperitoneally, produced a marked and progressive hypotensive response of rapid onset (20 min) in DS-rats the same dose intravenously produced a smaller response of delayed onset (80 minutes).

6 In anaesthetized DS-rats, an equivalent degree of cardiac β-adrenoceptor blockade was produced by pretreatment with pindolol, 50 μg/kg orally (2 h previously) or intravenously (1 h previously).

7 After administration of pindolol, 2 mg/kg intravenously, to conscious DS-rats, the tachycardia produced by intravenous isoprenaline, 3 μg/kg, was almost abolished for the first 60 min of the study, whereas a hypotensive response to pindolol was delayed in onset (100 minutes).

8 The hypotensive response and tachycardia produced by oral pindolol 50 μg/kg, in DS-rats were prevented by inhibition of metabolic enzyme activity by pretreatment with Proadifen (SKF 525-A), 80 mg/kg.

9 The results suggest that pindolol's effects on blood pressure and heart rate in the conscious DS-rat are mediated by a metabolite(s) acting by stimulation of peripheral β-adrenoceptors.

     

Electrophysiological effects of the salicylates on isolated atrial muscle of the rabbit

1 Intracellular recordings were made from cells of the sinoatrial (S-A) node region and from atrial muscle fibres of rabbit hearts. The effects of sodium salicylate and 5-bromo salicylate on various parameters of the membrane action potential were studied.

2 5-Bromo salicylate (30-100 μM) and sodium salicylate (300-500 μM) caused a dose-dependent decrease in the frequency of discharge of the SA node cells. Applications of atropine (2.6 μM) with propranolol (3.3 μM) did not affect the negative chronotropic effect, whereas adrenaline (5 μM) reversed it.

3 Depolarization and shortening of the action potential duration were found in atrial muscle fibres after the application of 5-bromo salicylate (60-100 μM). The reduction of the action potential duration (APD) was not affected by atropine (2.6 μM).

4 Higher concentrations of 5-bromo salicylate (> 100 μM) also caused a dose-dependent reduction in the action potential amplitude (APA), in the overshoot (OS) of the action potential and in the maximum rate of rise of the action potential (V_max). All these effects were completely reversed on washing.

5 Substitution of the NaCl of the bathing Tyrode solution by an equimolar concentration of Na isethionate did not affect the plateau depression induced by the salicylates in atrial muscle fibres.

6 After increasing the K concentration to 27 mM in the presence of isoprenaline (1 μM), `slow responses' were obtained upon stimulation. 5-Bromo salicylate (20-60 μM) and sodium salicylate (100 μM) decreased reversibly the amplitude and the rate of rise of the `slow response'.

7 A four fold increase in Ca concentration of the standard Tyrode solution did not antagonize the plateau depression of atrial muscle fibres or the negative chronotropism induced by salicylates.

8 Addition of CsCl (10 mM) to the Tyrode solution did not affect the shortening of the APD induced by the salicylates in atrial muscle fibres.

9 When the K concentration in the Tyrode solution was increased from 2.7 mM to 5.4 mM, the effects of 5-bromo salicylate on the APA, OS and V_max were potentiated. However, a significant reduction in the shortening of the APD produced by the salicylate was observed.

10 It is suggested that the salicylates possibly depress the slow inward current in both S-A node cells and atrial muscle fibres of the rabbit heart. In atrial muscle fibres, a concomitant increase in the outward potassium current is probably involved.

     

Impairment of cognitive function associated with hydroxyamylobarbitone accumulation in patients with renal insufficiency

1. Sodium amylobarbitone was given by intravenous infusion to six patients with chronic renal insufficiency and to six healthy volunteer subjects. Serum concentrations of amylobarbitone and its major metabolite hydroxyamylobarbitone were measured by a gas chromatograph method.

2. The serum concentrations of amylobarbitone were consistently lower in the patient group than in the control group and the concentration half time was shorter (0·10>P>0·05); the 48 h urinary excretion of hydroxyamylobarbitone was reduced (P<0·001) and the serum concentrations of hydroxyamylobarbitone were consistently raised.

3. When two patients were given 200 mg of sodium amylobarbitone daily over five consecutive days the serum concentration of hydroxyamylobarbitone rose steadily to a maximum of about 8 μg/ml. The serum concentrations in two healthy control subjects did not exceed 0·5 μg/ml.

4. Three parallel tests of cognitive function (Otis matched test forms A, B and C) were given to 16 control patients and to 12 amylobarbitone-treated patients. Significant impairment of performance was observed in test B (P<0·001) at a time when amylobarbitone only could be detected in the patients' serum, and in test C (P<0·001) when amylobarbitone concentrations were very low (0·52±0·08 μg/ml±SEM) but hydroxyamylobarbitone concentrations were still high (3·30±1·23, μg/ml±SEM).

5. There was a strong (r=-0·71) and significant (P<0·01) negative correlation between the performance in test C and the serum concentration of hydroxyamylobarbitone. It is concluded that hydroxyamylobarbitone has cerebral depressant effects in man.

     

Electrophysiological actions of Mexiletine (Köl 173) on canine Purkinje fibres and ventricular muscle

1 The effects of mexiletine (Kö1173) were investigated in canine isolated cardiac Purkinje fibres and ventricular muscle with microelectrodes. Some Purkinje fibres were depolarized by mechanical stretch to induce spontaneous activity with slow upstroke velocity. The preparations were stimulated at rates of 1, 2, 3 and 4 Hz. The drug concentrations tested were 0.4, 2 and 10 μg/ml in Tyrode solution (KCl = 5.4 mM).

2 The `therapeutic' drug concentration (2 μg/ml) shortened action potential duration and effective refractory period of Purkinje fibres, the effect being pronounced at lower stimulation rates. In ventricular fibres, action potential duration changes were not consistent while the effective refractory period was prolonged.

3 In depolarized Purkinje fibres showing automatic activity, the drug (0.4 or 2 μg/ml) depressed phase 4 depolarization and reduced the firing rate without changing maximum diastolic potential. However, when depolarized Purkinje fibres were electrically driven at a constant rate, the maximum diastolic potential became more negative with a concomitant decrease of pacemaker slope and increase of maximum rate of rise (_max) of action potentials.

4 Moderate (2 μg/ml) to high (10 μg/ml) concentrations of the drug depressed _max in Purkinje fibres stimulated at 2 Hz by 12 and 42% respectively and depressed `membrane responsiveness'. The decrease in _max depended upon the stimulation rate, being minimum at the lowest (1 Hz) and maximum at the highest (4 Hz) stimulation rate.

5 The drug (2 μg/ml) improved _max of the earliest propagated premature action potentials by shifting the takeoff potential to more negative levels in both Purkinje and ventricular fibres.

6 Membrane conductance in fibres mounted in a single sucrose gap chamber was increased by the drug (2 μg/ml) in both fibre types in normal and in Na⁺-deficient solutions. This increase was attributed to an increase in membrane K⁺ permeability produced by the drug.

7 All these effects are similar to those of lignocaine, diphenylhydantoin or aprindine, and can explain the antiarrhythmic action of mexiletine.

     

Hyperthermic responses to central and peripheral injections of morphine sulphate in the cat

1 The effect of morphine on body temperature was studied in conscious, unrestrained cats provided with implanted third or lateral cerebral ventricular cannulae, jugular venous catheters and retroperitoneal thermocouples.

2 Intraventricular injections of 2.5-50 μg and intravenous injections of 1-10 mg/kg morphine sulphate produced dose-related hyperthermic responses. Similar mean increases in body temperature after administration of a given dose were elicited in cats which had not previously received morphine and, provided that tolerance was avoided by spacing injections at least 72 h apart, in cats which received a series of injections of morphine. Morphine was at least 850 times more potent when injected into the third ventricle than when given intravenously. Increasing the dose of morphine sulphate injected into the third ventricle to 1250 μg only prolonged the hyperthermia. Morphine did not produce hypothermia at any dose tested.

3 Injection of 10 μg morphine sulphate into the third ventricle produced similar hyperthermias at ambient temperatures (tas) of 4-6, 21-23 and 33-36°C. The increase in body temperature was associated with shivering at the lower tas. At the highest ta, shivering was not evoked, but respiratory rate decreased after morphine if it was initially elevated. These results suggest that morphine increased the level at which body temperature was regulated.

4 Neither metiamide nor indomethacin antagonized morphine so histamine and prostaglandins were apparently not required for the hyperthermic effect.

     

Calcium antagonists: effects on cerebral blood flow and blood-brain barrier permeability in the rat

1 Because they affect isolated cerebral arteries, some calcium antagonists have been studied on the intact cerebral circulation of the rat.

2 Global cerebral blood flow (¹³³Xe clearance technique) was measured in anaesthetized rats. Neither perhexiline (0.1 μg/kg to 1.0 mg/kg, i.v.) nor diltiazem (0.06-0.6 mg/kg, i.v.) had any significant effect on resting cerebral blood flow when measured 5 min after each dose. A high dose of nifedipine (1.0 mg/kg, i.v.) was administered during induced hypocapnia. Nifedipine failed to modify the hypocapnic vasoconstriction of the cerebral vasculature when compared to vehicle-treated rats.

3 The possibility of discrete changes in regional cerebral blood flow was investigated. Local cerebral blood flow was measured in a number of brain regions by the [¹⁴C]-ethanol technique 15 min after the administration of nifedipine (20 or 100 μg/kg, i.v.). Nifedipine had no apparent effect on regional blood flow in the rat brain.

4 Acute arterial hypertension increases protein leakage into the brain, a phenomenon susceptible to drugs that act on endothelial pinocytosis which is known to be calcium-dependent. The increase in protein extravasation, induced by the intravenous administration of either angiotensin II or adrenaline, was unchanged in rats previously treated with either nimodipine (20 μg/kg, i.v.) or nifedipine (50 μg/kg, i.v.) when dissolved in ethanol alone. However, nifedipine (20 μg/kg, i.v.) when dissolved in a solution of polyethylene glycol and ethanol further enhanced the hypertension-induced increase in brain albumin permeability.

5 In conclusion, we have been unable to demonstrate any apparent effects of various calcium antagonists on the intact cerebral circulation of the rat, despite the number of different experimental models used.

     

The effects of sodium cromoglycate on lung irritant receptors and left ventricular cardiac receptors in the anaesthetized dog

1 The time from the injection of sodium cromoglycate 10 to 50 μg/kg into a saphenous vein, the cervical carotid arteries, the left ventricle and the aortic arch, to the onset of reflex hypotension has been measured in anaesthetized dogs. The shortest latency was 16.9 s on injection of sodium cromoglycate into the left ventricle.

2 Instillation of 2% lignocaine into the pericardium of an anaesthetized dog blocked the reflex hypotensive response to sodium cromoglycate (10 to 50 μg/kg i.v.), and also prevented sodium cromoglycate (100 μg/kg) from reversing reflex bronchoconstriction induced by inhalation of an aerosol of histamine.

3 The effect of sodium cromoglycate (100 μg/kg i.v.) on resting discharge and histamine-induced discharge (20 μg/kg i.v.) of five lung irritant receptors in five anaesthetized dogs has been studied. Sodium cromoglycate (100 μg/kg i.v.) did not affect the resting discharge of these receptors or their ability to respond to histamine.

4 Sodium cromoglycate (100 μg/kg i.v.) increased the rate of discharge of three receptors found in the endocardium of the left ventricle of the canine heart. A solution of sodium cromoglycate (0.1%) was applied topically to one receptor and its rate of discharge was increased.

5 It is suggested that in the dog, sodium cromoglycate produces reflex hypotension and reverses histamine-induced reflex bronchoconstriction by activating receptors in the left ventricle of the heart.

     

An electroencephalographic investigation of short-term effects of three hypothalamic hormones (TRH, LH/FSH-RH, GH-RIH) in normal subjects

1 Three hypothalamic regulatory hormones, thyrotrophin-releasing hormone (TRH), luteinizing hormone/follicle-stimulating hormone-releasing hormone (LH/FSH-RH) and growth hormone-release inhibiting hormone (GH-RIH) given intravenously had no effect on the electroencephalographic response known as the contingent negative variation (CNV) in normal subjects.

2 TRH was given as a 10 ml infusion of 600 μg over 8 min to six subjects. This produced subjective sensations and a rise in heart rate but no significant alteration of CNV magnitude.

3 LH/FSH-RH was given in a dose of 200 μg in 10 ml over 2 min to six subjects. This had no effect on CNV magnitude or heart rate and produced no subjective effects.

4 GH-RIH was given as a 10 ml infusion of 250 μg over 10 min to six subjects. Again there was no alteration in the magnitude of the CNV; the heart rate was slowed.

     

Interaction of albumin and fusidic acid

1. By combining the agar plate diffusion technique for determination of antibiotic activity and zone microelectrophoresis in agar gel, the activity of fusidic acid in individual serum proteins of blood and pus obtained from patients given sodium fusidate revealed albumin to be responsible for the protein binding of this antibiotic.

2. Based on the assumption that only free fusidic acid is microbiologically active, the relationship between the concentration of albumin and the ratio of free to total fusidic acid was determined at four concentrations of free fusidic acid, using as test organisms four differently sensitive variants of a Staphylococcus aureus strain. At each concentration an increasing amount of albumin (0-40 mg/ml culture medium) decreased the activity of fusidic acid as determined in serial dilutions (IC50).

3. The law of mass action expressed as Langmuir's adsorption isotherm was valid if a correction for the influence of albumin on the sensitivity of the strain of Staph. aureus was introduced. For other test organisms no correction is necessary. The constant in Langmuir's adsorption isotherm was K=78400±8200 l./mol and n=3·15 (95% confidence limits: 2·09-5·52).

4. The mean blood concentration was 20·8 μg/ml and the mean pus concentration 17·2 μg/ml in nineteen sets of blood and pus samples. The ratio of pus to blood corresponds to the ratio of published values for the protein concentrations in serum and in inflammatory oedema.

5. It is concluded that for albumin bound drugs the `storage depot' of the organism also includes the fluid of the tissue spaces including the inflammatory oedema. As recent studies have revealed an extravascular albumin pool similar in size to the plasma pool, this `storage depot' should not be neglected.

     

Effect of caroxazone, a new antidepressant drug, on monoamine oxidases in healthy volunteers

1 Caroxazone is a new antidepressant drug with a reversible inhibitory effect on monoamine oxidases (MAO) as previously shown experimentally in animals.

2 The effect of caroxazone on MAO was explored in healthy volunteers and compared with that of tranylcypromine and imipramine. Daily urinary excretion of tryptamine and MAO activity in platelets were assayed at various times during and after treatment and the differences from basal values were statistically analysed. In addition, caroxazone plasma levels were determined.

3 Caroxazone administered orally at doses of 300 or 600 mg/day for 12 days induced a significant, dose-dependent increase in urinary tryptamine excretion. Tranylcypromine (20 mg/day for 8 days) was even more active in this respect; imipramine (50 mg/day for 12 days) was completely inactive.

4 MAO activity in platelets was not affected by caroxazone or imipramine, but was completely inhibited by tranylcypromine.

5 Mean steady-state plasma levels of caroxazone were about 6 μg/ml and 11-12 μg/ml with the dose of 300 mg/day and 600 mg/day respectively.

6 It can be concluded that caroxazone is a MAO inhibitor in man too, at a clinically effective dose such as 600 mg/day. The fact that its MAO inhibition is not apparent in platelet preparation may be explained by its reversibility.

7 Tranylcypromine confirmed its potent irreversible MAO inhibitory effect, while imipramine lacked any effect at the tested dose.

     

The influence of elevated plasma hydrocortisone concentrations on antipyrine metabolism in man

1 The plasma half-life of antipyrine was estimated overnight in four healthy volunteers on two separate occasions, one during i.v. infusion of hydrocortisone (3 mg/h) and the second during an infusion of normal saline.

2 The plasma fluorogenic corticosteroid concentration averaged 12.5 μg/100 ml during saline infusion, increasing to 20.1 μg/100 ml during hydrocortisone infusion.

3 The mean antipyrine half-life increased from 9.7 h during saline infusion to 12.6 h during hydrocortisone infusion.

4 No consistent change was found in the apparent volume of distribution or urinary excretion of antipyrine, or of the urinary excretion of D-glucaric acid.

5 The stimulation by hydrocortisone of antipyrine metabolism demonstrated by other workers has not been found.

     

The effects of acetylcholine on the membrane and contractile properties of smooth muscle cells of the rabbit superior mesenteric artery

1 Effects of acetylcholine (ACh) on the membrane potential and mechanical properties of rabbit superior mesenteric artery were investigated by the use of microelectrode and isometric tension recording methods. The membrane potential was -62.5 ± 3.0 mV (s.d.). The maximum slope of the membrane depolarization produced by tenfold increase in [K]₀ plotted on a log scale was 48 mV. Excess [K]₀ and low [K]₀ depolarized the membrane and produced contraction (contracture). The minimum depolarization to produce contraction was 10 mV.

2 Low concentrations (10 and 100 ng/ml) of ACh hyperpolarized the membrane. Increased concentrations of ACh (1 and 10 μg/ml) hyperpolarized the membrane further in adult rabbit, while increased concentrations of ACh produced a smaller hyperpolarization in young rabbit. These potential changes produced by ACh in immature and adult rabbits were suppressed by treatment with atropine (0.1 μg/ml).

3 ACh (10 ng to 1 μg/ml) consistently generated contraction in Krebs solution. However, ACh relaxed the contraction induced by either K⁺ or noradrenaline in the adult rabbit, and it enhanced contraction produced by this treatment in the immature rabbit. In Ca-free EGTA solution, the action of ACh on the mechanical response was markedly suppressed, although high concentrations of ACh still evoked contraction. However, treatment with atropine (1 μg/ml) completely prevented these actions of ACh.

4 ACh-induced relaxation during either K⁺-induced or noradrenaline-induced contraction was not caused by the hyperpolarization of the membrane.

5 It is concluded that ACh possesses dual actions on smooth muscle cells of the rabbit superior mesenteric artery in Krebs solution, i.e. ACh hyperpolarizes the membrane, while it consistently generates contraction. These ACh actions on the muscle cells were modified by aging.