Plasma Disappearance of Injected Synthetic LRH in Man as Measured by Bioassay and Radioimmunoassay

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Abstract
Synthetic LRH was injected iv as one pulse (100–200 μg) to 6 healthy men. Plasma and urine LRH were bioassayed (increase of plasma radioimmunoassayable LH in the rat); plasma LRH and LH were measured by radioimmunoassay (RIA). Plasma LH rose maximally from 28 ± 3 to 345 ± 90 ng/ml (mean ± se, LER-907) after injection. The disappearance of LRH from plasma was rapid, t½ = 2.9 min when measured by bioassay and t½ = 2.7 min when measured by RIA within the first 5 min. Plasma LRH was not detectable after 20 min by bioassay, and varied from 0.8 to 4 ng/ml at 60 min when measured by RIA. LRH measured by RIA or by bioassay generally gave comparable results. Urine LRH was detectable by bioassay at 20 and 60 min only (1.5–2.4 ng/ml). When synthetic LRH was incubated in human plasma at 37 C for 90 min, no bioassayable loss of activity was found. LRH also was incubated in human plasma and submitted to gel filtration (Sephadex G-200) and LRH activity was found to be eluted after the major proteins, indicating that exogenous LRH is not evidently bound to major plasma proteins.

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