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A radioimmunoassay (RIA) for the measurement of activin A, which is identical to erythroid differentiation factor (EDF), has been developed. A specific antiserum against activin A/EDF was raised in rabbits using a mixture of recombinant EDF and polyvinyl pyrrolidone. Of the compounds tested this polyclonal antibody cross-reacted only with bovine inhibin (3.2%) and human TGF-β (4.2%). The least detectable value in this assay was 0.06 ng/tube. The within- and between-assay coefficients of variation at three different concentrations were 3.6–9.8% and 3.4–7.7%, respectively. Using this RIA, immunoreactive activin A/EDF levels in various biological fluids and tissues were examined. The dose-response curves of porcine follicular fluid and ovarian extract were parallel to the standard curve, and porcine follicular fluid contained high activin A/EDF immunoreactivity (1050 ng/ml). On gel chromatography of porcine follicular fluid, the major immunoreactivity was eluted in the same position as authentic activin A/EDF. Human placental extract and amniotic fluid had relatively high immunoreactive activin A/EDF levels (174 ng/g wet wt. and 63.9 ng/ml, respectively), but the dose-response curve of amniotic fluid was not parallel to the standard curve. Among rat tissues, the ovary showed the highest activin A/EDF immunoreactivity (163 ng/g wet wt.) much lower than that of porcine ovary (1020 ng/g wet wt.). Low immunoreactive activin A/EDF levels were detected in most parts of rat brain (8.7–14.2 ng/g wet wt.), except for the pituitary gland (70.0 ng/g wet wt.). The initial plasma half clearance time (t 1 2 ) of exogenous activin A/EDF was 14 min in the rat and the plasma FSH concentration did not change significantly during this period. These results suggests that this RIA system has sufficient sensitivity and specificity to measure activin A/EDF concentrations in biological materials, and that the reproductive tissues are the main sources of activin A/EDF.

A sensitive and specific radioimmunoassay is described for plasma and urinary levels of [D-Ser(tBu)]6des-Gly-NH2(10) ethylamide (buserelin). No appreciable cross-reaction (less than 0.05%) was observed with LH-RH and its analogs other than buserelin fragments (1.6-45%). The sensitivity was 3 pg per tube. At buserelin concentrations of 125, 250 and 500 pg/ml, the intra- and inter-assay coefficients of variation were 7.9, 10.0 and 10.0%, and 19.0, 7.8 and 6.8% respectively. Recovery of buserelin added to plasma was quantitative (62.5 pg/ml, 101.6%; 125 pg/ml, 76.8% and 250 pg/ml, 63.4%). A dose of 5 micrograms buserelin injected subcutaneously into 5 normal male adults, reached a peak plasma level in 45 min (mean value 119.3 +/- 47.3 pg/ml) and remained detectable for at least 4 h. The half disappearance time was 118.8 +/- 26.0 min. Between 9 and 16% of the administered dose was excreted in the urine within 24 h. Buserelin could also be detected in the plasma after intranasal administration of doses of 150, 300 and 450 micrograms. There was a significant difference in the area under the curve (AUC) for plasma levels after subcutaneous injection of 5 micrograms and intranasal administration of 150 micrograms, but not between the AUC values after the three intranasal doses. These results indicate that this method for radioimmunoassay of buserelin is suitable for analyzing the pharmacokinetics and bioavailability of buserelin in man.