Distribution of radioactivity in the organs of the rat and mouse after injection of (125I)alpha-melanocyte-stimulating hormone.

The distribution of radioactivity after intrajugular injection of 125I-labelled alpha-melanocyte-stimulating hormone (alpha-MSH) was studied by whole-body autoradiography of the mouse and by direct measurement of radioactivity in individual organs of the rat. Very high uptake of radioactivity in the pineal gland was measured 5 min after the injection of (125I)alpha-MSH. Lower levels of accumulation of radioactivity were found in the kidney and in the posterior (including intermediate) lobe of the pituitary. High uptake was also found in the thyroid, stomach, and oesophagus. The specificity of uptake of (125I)alpha-MSH into the pineal and pituitary is suggested by the very low uptake of Na125I into those tissues.