The distribution in the rabbit of choline administered by injection or infusion.

1. The concentration of choline in plasma, erythrocytes, skeletal muscle, heart, lung, liver, small intestine and kidneys and the changes that follow the injection or infusion of choline have been measured in rabbits anaesthetized with pentobarbitone.2. The concentration of choline in the plasma of arterial blood was 11.8 +/- 0.6 n-mole/ml. and in the erythrocytes 28.4 +/- 1.3 n-mole/ml. blood.3. All tissues contained a higher concentration of free choline than did plasma. The values range from 19.1 +/- 2.2 n-mole/g in skeletal muscle to 500 +/- 25 n-mole/g in the kidney.4. In order of their choline concentrations the tissues were intestine (duodenal end) > kidney > intestine (caecal end) > liver > lung > brain > heart > erythrocytes > (blood) > skeletal muscle > plasma, while in order of the contribution to the total body choline they were liver > intestine > skeletal muscle > (blood) > kidney > erythrocytes > lung > brain > plasma > heart. The total free choline determined by these analyses was between 30-40 mumole/kg body weight, about one third being present in the liver.5. The choline content of the small intestine varied along its length. The lowest amount being present in the portion adjoining the caecum.6. Within 1 min of the injection of choline 100 or 300 mumole/kg, 70-90% had left the circulation. The proportionate loss was higher after 100 mumole/kg than after 300 mumole/kg.7. The loss following 300 mumole/kg was increased if that dose were preceded by a dose of 100 mumole/kg 40 min earlier; this suggests some additional disposal mechanism(s) had been activated by the first dose.8. Three minutes after the injection of choline 300 mumole/kg, about 60% was present as free choline in the tissues studied. The order of the concentration increases was kidneys > liver > muscle > lung > small intestine (caecal end) > heart > intestine > small intestine (duodenal end) > brain.9. Forty minutes after the injection of choline 300 mumole/kg, only 11% could be accounted for as free choline. Only the levels in the kidney, liver, muscle and lung were significantly above normal at this time.10. Infusion of choline 0.8 mumole/kg. min or greater produced rises in plasma choline that corresponded to a clearance of 32 ml. plasma/kg. min.11. After the infusion of 300 mumole/kg over a period of 1 hr, raised levels of choline were detected in all tissues assayed, but the amount found accounted for only 14% of the choline administered. The concentrations in the kidney, liver and lung were similar to those found 40 min after the injection of 300 mumole/kg.12. There was no change in the concentration of choline in the erythrocytes after the injection of choline 100 or 300 mumole/kg, nor during the infusion of choline at the rate of 5 mumole/kg. min for 1 hr.13. The plasma volume appeared to be affected by the injection of the large doses of choline; after choline 300 mumole/kg the plasma volume was reduced. No effect on the plasma volume was observed during the infusion of the same dose.