Measurement of Prolactin Activity in Human Serum by the Induction of Specific Milk Proteins in Mammary Glandin Vitro

Abstract

The quantitative relationship between the prolactin concentration and the rates of induction of the specific proteins casein and lactose synthetase have been studied in mouse mammary explants incubated on medium containing human serum. Increases in the synthesis of ³²P-casein and in the activity of N-acetyllactosamine synthetase were proportional to the log concentration of ovine prolactin in the medium over the range 2–1000 ng/ml. Human growth hormone at concentrations greater than 10 ng/ml medium caused a significant stimulation, but this activity could be completely removed by pretreatment of the medium with antihuman growth hormone antiserum. Human chorionic somatomammotrophin exhibited a potency similar to that of ovine prolactin, but no other hormones interfered with the bioassay of prolactin. Dilutions of human serum containing prolactin activity paralleled the activity of the ovine prolactin standards over the entire concentration range of the ³²P-casein bioassay. The within assay precision was represented by a standard deviation which never exceeded ±10%, and excellent agreement was observed between assays. The lowest detectable concentration was considered to be 2 ng/ml serum (0.06 mU/ml serum). Elevated prolactin activity was found in all patients with clinically significant galactorrhea or with post-partum lactation, with serum values ranging from 0.54 to 56.0 mU/ml. These studies indicate that the induction of ³²P-casein or N-acetyllactosamine synthetase can be utilized as a sensitive and specific bioassay which can yield meaningful clinical data on prolactin activity in human serum with a high degree of statistical accuracy.