Karoly Nikolics

Distribution of 3H-α-MSH in rat brain

Abstract Radioactive synthetic α-MSH, prepared by selective tritiation of its dibromo-L-tyrosine2-derivative, was injected into the carotid artery of intact, hypophysectomized or pinealectomized rats. More radioactivity was found in the occipital cortex, cerebellum, and pons-medulla than in most other brain parts of rats decapitated 15 sec and, to a less significant extent, 30 min after injection. Part of this radioactivity behaved like α-MSH in several identification procedures. After administration of 3H-tyrosine, the least radioactivity was consistently found in the pons-medulla. Large amounts of radioactivity after 3H-α-MSH were found in the pituitary and, particularly in the hypophysectomized rats, in the pineal. The half-time disappearance of the first component of radioactivity from the blood of each group of rats injected with tritiated-α-MSH was no more than 2.5 minutes, a time considerably shorter than the behavioral and EEG effects of this pituitary hormone on visual attention.

Disappearance and excretion of labeled α-MSH in man

Abstract Despite the considerable evidence for the CNS actions of α-melanocyte-stimulating hormone (α-MSH) in man, little attention has been given to its half-time disappearance from plasma and urinary excretion in normal individuals. In the first experiment, a healthy man was given 15 μCi of tritiated ( 3 H)-α-MSH as a rapid IV injection. A plot of the disappearance time in plasma was characteristic of a multiexponential curve, the linear components of which were resolved by the subtraction method and half-time disappearance calculated directly from the slope of the regression line. The half-time disappearance was 1 min for the first component and 25 min for the second component. After the IV administration of 50 μCi of 125 I-α-MSH in the second experiment, the two components showed halftime disappearances of 1 min and 4.8 min respectively. These times were not changed by precipitation of the plasma with 10% trichloroacetic acid. Thirty-eight percent and 42% of the label appeared in the urine 4 hr after the injection of either 3 H-α-MSH or 125 I-α-MSH. The results suggest that the persistence of high levels of α-MSH in the blood after injection in man may be too short to fully explain the CNS effects of α-MSH.