ACETYLCHOLINE RELEASE IN CEREBROSPINAL FLUID BY OUABAIN J. A. RIBEIRO and F. PERES-COMES Laboratory of Pharmacology, Gulbenkian Institute of Sciences. Oeiras.

Portugal

Summary--0uabain increased the acetylcholine and potassium levels in the effluent collected from cisterna magna in cats anaesthetized and with the cerebral ventricles perfused with artificial cerebrospinal fiuid. These cffccts were not modified by tetrodotoxin.

ice. The samples were assayed against standard solutions of acetylcholine Ion the arterial pressure of a cat. All samples contaminated with blood were discarded and the experiment ended. The action of ouabain on acetylcholine release was studied in 4 groups of animals as follows:

It has been shown that cardiac glycosides increase the release of acetylcholine from sympathetic ganglia (Konzett and Rothlin, 1953 ; Perry and Reinert. 1954). motor-nerve terminals (Birks. 1963, Elmqvist and Feldman. 1965). nerve terminals in the guinea-pig ileum (Paton, Vizi and Zar. 1971) and from cortical slices (Vizi, 1972; Grewaal and Quastel, 1973). On the other hand tetrodotoxin (TTX) decreases the release of acetylcholine from the exposed cerebral cortex of anaesthetized cats (Dudar and Szerb, 1969). In previous studies (Peres-Gomes and Ribeiro unpublished; Ribeiro, 1976) it was observed that TTX, given intracerebroventricularly, protected against ouabain arrhythmias and blood-pressure effects. Therefore it seemed of interest to study the effects of ouabain on acetylcholine release from cats pretreated with TTX and concomitantly to look at the sodium and potassium levels in cerebrospinal fluid in the absence and in the presence of TTX. METHODS Male adult cats were anacsthetized with chloralose, 80mgikg injected into a femoral vein. The trachea and femoral artery were cannulated for artificial respiration and arterial pressure recording. Heart rate was recorded with a cardiotachometer triggered by the pressure pulse. Electrocardiogram (usL\ally Lead II) was recorded simultaneously with the other parameters. The cerebral ventricles were perfused, using the technique described by Bhattacharya and Feldberg, (1958) with artificial cerebrospinal fluid (Merlis, 1940) containing 5 /‘g/ml of neostigmine methylsulphate. The perfusion was carried out from the left lateral ventricle of the brain to the cisterna magna at a rate of 0. I ml/min. The effluent was collected every 30 min in tubes containing 0.1 ml of HCI N/3 surrounded by KCJ~ Words-ouabain. potassium, tetrodotoxin. Mailing macology. gal.

cerebrospinal

First group: ouabain was injected intravenously (20 pgg!kg) every 30 min until ventricular fibrillation occurred. The control was carried out in open chest animals inducing the ventricular fibrillation by electrical stimulation, aconitine or potassium chloride directly applied on the external surface of the cardiac ventricles. Second group: two hours after the beginning of the ventricular perfusion. ouabain was added to the perfusion fluid into the lateral ventricle of the brain at a rate of 3 icg/min until the development of ventricular fibrillation. Third group: ouabain was administered in the same way as in the second group at a rate of 6pg/min but only for 60 min. Fourth group: ouabain was used as in the third group. Tetrodotoxin was present during all the ventricular perfusion starting 2 hr before the beginning of ouabain administration. Two concentrations of tetrodotoxin were used, given at rates of 6.6 ng/min and 33.3 ng/min.

fluid, acetylcholine,

address: Dr .I. A. Ribeiro. Laboratory of PharGulbenkian Institute of Sciences, Oeiras, Portu-

695

The sodium and potassium concentration of the samples were dctermincd by flame photometry. The significance of differences between means was determined by Student’s t-test. RESULTS The perfusion of the cerebral ventricles with artificial cerebrospinal fluid containing neostigmine did not change the blood pressure, heart rate or electrocardiogram for the time of the perfusion. even when carried out for 3-4 hr. In the first group of cats the samples corresponding to the terminal phase of the ouabain intoxication by the intravenous route presented an increase of acetylcholine levels (Table I ). However, a further increase

J. A. RIBEIROand F. PERES-G• MES

hYh

Table

1. Acetylcholine

content

of the cerebrospinal

fluid in different Acctylchohne

Experimental

conditions

30

Acetylcholine release in cerebrospinal fluid by ouabain.

ACETYLCHOLINE RELEASE IN CEREBROSPINAL FLUID BY OUABAIN J. A. RIBEIRO and F. PERES-COMES Laboratory of Pharmacology, Gulbenkian Institute of Sciences...
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