Relationships between alpha-MSH levels in blood and in cerebrospinal fluid.

Using a new cannulation technique of the cisterna magna of the rat, CSF was obtained in which alpha-MSH levels were determined under various conditions and were compared with alpha-MSH levels in plasma. Basal levels of 66 +/- 9 pg alpha-MSH/ml were found in the CSF and of 179 +/- 13 pg alpha-MSH/ml in the plasma. A rapid flow of CSF from the lateral ventricles to the cisterna magna could be established as detected by elevated alpha-MSH levels in cisternal CSF 2 min after injection of a large quantity of alpha-MSH into the ventricular system. A half-time disappearance of alpha-MSH from the CSF of 33 min was calculated. The possibility of a contribution of peripheral alpha-MSH to central melanotropic activity was suggested by the finding of elevated levels of alpha-MSH in the CSF, following artificially induced high alpha-MSH concentrations in the blood. Additionally, the movement of alpha-MSH from the CSF to the blood was demonstrated. Both these movements were shown to be independent of the pituitary gland, since hypophysectomized animals exhibited the same rate of alpha-MSH transport as intact animals.