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Relationship between Bioassay and Radioimmunoassay Estimates of Prolactin in Rat Serum^*

FREDERICK C. LEUNG, SHARON M. RUSSELL and CHARLES S. NICOLL

Department of Physiology-Anatomy, University of California Berkeley, California 94720

Abstract

RIA and bioassay (BA) estimates of the concentration of PRL ([PRL]) in rat serum were compared using homologous assay systems. A rat mammary gland organ culture BA was developed which allowed objective and quantitative measurement of serum [PRL]. The serum samples were tested at two doses against three doses of the RP-1 rat PRL standard and the responses were quantified by a histometric procedure. The index of precision of the BA ranged from 0.1–0.4 and the secretory response was not affected by physiological concentrations of rat GH, T₃, or by gonadal steroids.

Serum samples taken from female rats during the estrous cycle, from suckled lactators, from rats bearing a PRL-secreting pituitary tumor, and from females that were treated with perphenazine were assayed. A highly significant correlation (r = 0.99) was obtained between the two assay methods with 21 samples. However, the regression coefficient was 4.20 ± 0.55. Thus, although the two assays are highly correlated for measuring serum [PRL], the RIA measures only about 25% of the hormone that is detected by the mammary gland organ culture BA.

Footnotes

^* This work was supported by NIH Grant AM-13605, NSF Grants GB-42687 and PCM 76-14772, and funds from the Committee on Research of the University of California at Berkeley.

To whom requests for reprints should be addressed.

Received November 6, 1977.