Abstract
By modification of an in vitro rat bioassay (1), we have developed a micro-method which allows simultaneous incubation of 12 unknown samples each at 3 dose levels, using 1-10 μl of unextracted plasma. Testes of 8 to 10 weeks old rats are digested with collagenase; the separated interstitial cells are suspended in Medium 199 and incubated under O2/CO2 (95/5%) at 37°C for 3 hours. Testosterone (T) is measured by an 21 hours-RIA using 125-iodine labelled tracer. T production after incubation with 25 ng of the standard pituitary extract hLH LER 907 is about 8 times the basal value produced in the absence of gonadotropins (range of standard curve 0.5 - 25 ngLH; sensitivity 0.5 ngLH; between-assay variation at 25 ng level: 10%). LH values in human plasma determined with our bioassay are higher than RIA values. Our results show that Bio/RIA ratios vary at different RIA LH levels, the lowest so far measured being 2.0. The high bioassay values associated with low immunological LH values observed in some of our patients may help to clarify unexplained discrepancies between RIA results and clinical findings.(1) DUFAU et al, J.Clin Endocrinol Metab 42:958, 1976Supported by the Swiss National Science Foundation Grant No. 3.901.077
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