title: Plasma clearance in the rat of the LH bioactivity of two human LH standards of differing molecular composition.
abstract: The LH biological potency of the International Reference Preparation (IRP) of Human Pituitary LH for Immunoassay (IRP 68/40) relative to that of the 2nd IRP of Human Pituitary FSH and LH for Bioassay (IRP 78/549) is markedly greater when estimated by in-vitro interstitial cell testosterone production (TICT) bioassay than by in-vivo bioassay, and by the 4-h ovarian ascorbate depletion (OAAD) assay than by the 4-day seminal vesicle weight gain assay. Other preparations of human LH which, like IRP 68/40, were highly purified, showed a similar spectrum of bioactivity in these assay systems and also contained a higher proportion of more basic LH isoforms than are found in crude pituitary extracts such as IRP 78/549. In an attempt to explain these differences, a comparison was made of the plasma survival in rats of the LH bioactivity (by TICT assay) of these two preparations. Contrary to expectation, their relative plasma clearance rates over a 4-h period did not account for their differing bioactivities. The plasma half-life of the LH bioactivity (with 95% confidence limits) was estimated to be 42.4 (35.3-49.5) min for IRP 68/40 and 41.3 (31.5-51.0) min for IRP 78/549. Furthermore the time-course of action in vivo of IRP 78/549 did not appear to be more prolonged than that of IRP 68/40. Thus their plasma testosterone responses during the course of these 4-h plasma clearance studies were similar, and estimates of the LH potency of IRP 68/40 relative to that of IRP 78/549 were no greater by 2-h than by 4-h OAAD assay.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: National Institute for Biological Standards and Control, Hertfordshire.
authors.forename: P L
authors.initials: PL
authors.lastname: Storring
authors.forename: S A
authors.initials: SA
authors.lastname: Khan
authors.forename: Y G
authors.initials: YG
authors.lastname: Mistry
authors.forename: E
authors.initials: E
authors.lastname: Diczfalusy
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism; D001681:Biological Assay; D005260:Female; D006801:Humans; D007118:Immunoassay; D007536:Isomerism; D007986:Luteinizing Hormone / Q000097:blood* / Q000493:pharmacokinetics; D008297:Male; D008657:Metabolic Clearance Rate; D010053:Ovary / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012015:Reference Standards; D013739:Testosterone / Q000097:blood
chemical_list: D013739:Testosterone; D007986:Luteinizing Hormone; D001205:Ascorbic Acid