RADIOIMMUNOASSAY OF RAT PROLACTIN . COMPARISON OF RAT PROLACTIN PREPARATIONS ISOLATED FROM GRANULAR FRACTION OF PITUITARY TUMOUR TRANSPLANTS AND FROM NORMAL PITUITARY GLANDS

The performance in various procedures for radioimmunoassay of a rat prolactin preparation isolated from the 'granular fraction' of transplants of prolactin-producing pituitary tumours is compared to that of a prolactin preparation isolated from pooled frozen normal pituitary glands. Antisera titration curves and competitive inhibition curves indicate that the two preparations resemble each other closely. Analysis of covariance of competitive inhibition curves indicates that the small differences observed between the two preparations in recent assays can be ascribed to experimental error. Not withstanding a marked difference in biological activity between the two preparations as measured by the local pigeon crop assay, the reported experiments indicate that radioimmunoassays based on either of the two preparations will give approximately the same values when the prolactin estimates in biological material are expressed in unit weight aequivalents of the preparation employed. Expression in unit weight aequivalents should therefore be preferred to an extrapolation from these to i.u. of biological prolactin activity. © 1969.