Studies on the determination of plasma prolactin.

A double antibody solid-phase (DASP) and a plyethylene glycol (PEG) radioimmunoassay method for plasma prolactin determination were developed and evaluated as to their reliability. The iodination of prolactin was carried out using a lactoperoxidase sorbent with iodination conditions being optimized by studying the effect of reaction buffer pH in the range 5.0--7.0 at two ionic strengths. With the DASP-technique, intra-assay coefficient of variation was 6% (n = 30) and the inter-assay coefficient of variation 12% (n = 12), and with the PEG-technique, intra-assay coefficient of variation was 10% (n = 10). The sensitivity, with the DASP system, was 0.098 ng/tube and the detection limit for plasma, 0.8 microgram/l. The use of the PEG-technique was abandoned because of poor precision and nonparallelism of plasma dilution curves with the standard curve. The whole mean basal plasma value was 34.0 +/- 19.5 microgram/l (mean +/- 2SD, n = 35). The response after administration of 200 mg sulphiride was an increase of between 119--220% of basal values and after administration of 100 mg of chlorpromazine, an increase of 85--140%. After administration of TRH (thyrotropine releasing hormone) an increase of between 60 and 330% was obtained, the mean increments after 20 min in outpatients being 87.0 microgram/l and in hospitalized subjects, 51.2 microgram/l.