Extraction and partial purification of prolactin-release stimulating factor in bovine hypothalami

Partial purification of prolactin-release stimulating factor (PRF) was performed by Sephadex G-25 gel filtration of bovine hypothalamic extracts. PRF activity was evaluated on the basis of the measurement of immunoreactive prolactin released from the isolated rat hemipituitary in vitro. PRF activity was found in the fractions with Kav=0-0.49 and prolactin-release inhibiting activity was also detected in the fractions with Kav=0.69-0.89. The dose-response relationship was established between the partially purified PRF and its activity. The elution position of the partially purified PRF preceded that of TRH on Sephadex G-25. TRH at the dose of 100 nM stimulated the release of TSH in vitro, but not the release of prolactin. These results may indicate that there exists PRF with a relatively high molecular weight in the bovine hypothalamus.