More than 150 hypothalamic fractions were reassayed for luteinizing hormone releasing hormone (LHRH) and follicle stimulating hormone releasing hormone (FSHRH) activities in search for LHRH and FSHRH which differ from the decapeptide (pyro)Glu His Trp Ser Tyr Gly Leu Arg Pro Gly NH 2 (I). Among the porcine fractions tested were those obtained: 1) from the isolation of thyrotropin releasing hormone; 2) from two isolation procedures for LHRH; and 3) from methanolic and aqueous 2 N acetic acid extracts which were subjected to Biogel P-2 filtration and partition chromatography. Some bovine hypothalamic fractions were also tested. Both in vivo and in vitro assays were used for measuring LHRH and FSHRH activities. The values obtained were in each case compared with those resulting from the administration of pure natural or synthetic LHRH decapeptide I. A radioimmunoassay for LHRH (I) was also utilized for some fractions. In all the purification steps the location of LHRH and FSHRH activity, as determined by in vivo assays, corresponded to that of the decapeptide I. Purification of hypothalamic extracts on Biogel P-2 and by partition chromatography separated a fraction from the decapeptide I, which released more FSH than LH in vitro from the pituitaries of immature female rats. However, this material was inactive in vivo and in other in vitro systems, so that its significance is obscure. The results suggest that if material with LHRH and FSHRH activity other than the decapeptide I is present in acid extracts of porcine hypothalami, then its FSHRH and LHRH activity would be a minor part of the total LHRH/FSHRH activity in the extracts. (Pyro) Glu His Trp Ser Tyr Gly Leu Arg Pro Gly NH 2 appears to account for most of all of the LHRH and FSHRH activity found.
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