Intrinsic activity of labetalol on guinea‐pig isolated trachea

2-3 days. Nonetheless, our findings show that minipumps are suitable for administering lithium directly into the c.n.s. of rats on a long-term basis. The fact that the lithium concentration in blood is very much lower than the lithium concentration in the c.n.s. during long-term administration by minipumps suggests that the method may be of use to distinguish between peripheral and central actions of prolonged lithium treatment. We thank Vibeke Glud and Anne-Mette Nielsen for skilful technical assistance and P. Carl Petersen's Fund and the Danish Medical Research Council for financial aid.