Cholinolytic drugs differ widely in their relative central activities. With the quaternary and some tertiary amines, central activity is very small, whereas the antiparkinsonian drugs have a high central activity. Because the so-called blood-brain barrier is lipid in character and allows highly lipid-soluble substances to penetrate faster than poorly lipid-soluble substances, the question was investigated whether central activity is influenced by the lipid-solubility of the drugs.

Accordingly the partition coefficients heptane/water of the drugs were measured and compared with the relative central cholinolytic activities. The relative central activity was represented by the central to peripheral cholinolytic active doses. The two values were determined by different biologic methods: antiarecoline action, investigated by means of the analgesia test in the mouse; inhibition of the EEG arousal reaction in the rabbit; intensification of the morphine induced stupor in the rat; mydriatic action in mouse and rabbit; and inhibition of chromodacryorrhoea in the rat.

The results show a correlation between the relative central activity and the partition coefficient heptane/water of the drugs. This means that the relative central activity increases as the lipid-solubility of the drug increases.