Abstract
It is well established that secretion of prolactin by the pituitary gland in animals and humans is controlled by the hypothalamus by means of a hypothalamic neurohumor, prolactin release inhibiting factor (PIF) or hormone (1,2). Secretion of prolactin appears also to be regulated by a hypothalamic prolactin releasing factor (PRF) (1,2). Search for these neurohumors is in progress in our laboratory and several others. Our findings during the process of purification of PIF from the porcine hypothalamic tissue indicated that the fraction with highest PIF activity was rich in catecholamines. Catecholamines can suppress prolactin release in vivo and in vitro by direct action (3–5). The possibility has been raised that catecholamines may be the physiological PIF, but as of yet no concrete evidence has appeared to support this view. PIF activity in the extracts of the hypothalamus was also found in a fraction devoid of catecholamines. We wish to present recent data on the purification of a substance with PIF activity from porcine hypothalamic tissue.