Studies on the Purification of Ovine Prolactin-Inhibiting Factor

Abstract

After several extractions, hypothalamic extract was subjected to gel filtration on long columns of Sephadex G-25. Prolactin-inhibiting activity of the fractions was estimated by their ability to block suckling-induced decline in pituitary prolactin. This inhibitory activity was recovered in each of 5 f ractionations with Sephadex. In each instance the prolactin-inhibiting activity was found to be closely associated with luteinizing hormone (LH)-releasing activity as estimated by ovarian ascorbic acid depletion; however, in 3 of 5 experiments there was a tendency for the prolactin-inhibiting activity to be eluted from the column just prior to the emergence of the peak of the LH-releasing activity. When the zones with prolactin-inhibiting and LH-releasing activity from several columns were pooled, lyophilized and eluted from a carboxymethylcellulose column by application of ammonium acetate buffers of increasing pH and ionic strength, prolactin-inhibiting activity was again recovered from the column in fractions which also possessed LH-releasing activity. The peptide content in the highly purified prolactin-inhibiting factor (PIF) was estimated to be < 3 [mu]g. Clearly, a manyfold purification of PIF was achieved without obtaining a clear-cut separation from the LH-releasing factor (LH-RF). The PIF was partially separated from follicle stimulating hormone-RF and removed from the zones which contained growth hormone-RF, melanocyte stimulating hormone-RF, thyrotropin-RF and vasopressin.