Immunologic and biologic characteristics of human decidual prolactin.

An increasing and consistent production of prolactin by decidual tissue (dhPRL) has been shown during a 24-hour incubation in a chemically defined buffer medium. No difference in dhPRL release was observed in tissue obtained from first- and third-trimester pregnancy. Estradiol had neither a stimulatory nor an inhibitory influence on dhPRL release, although release of this polypeptide by decidual tissue incubated with cycloheximide was blocked. The precise mechanism controlling the production and release of dhPRL is not known. Addition of theophylline, dibutyryl cyclic adenosine monophosphate, or guanosine triphosphate had no effect on dhPRL release during a 4-hour incubation. In contrast, these substances provoked a statistically significant increase in PRL release from rat hemipituitaries coincubated in vitro. Displacement curves for dhPRL against a human PRL standard suggest molecular homogeneity between both hormones. The biologic activity of dhPRL was next confirmed by means of a new bioassay system with a lower level of sensitivity of 20 pg/ml. In addition, dissociation of the biologic and immunologic activity of dhPRL has been completed and suggests that at least three isohormones are produced by human decidual tissue. The dhPRL production rate per gram of decidual tissue wet weight is far below that reported for the pituitary homologue. These studies not only provide confirmatory evidence of the immunologic and biologic activity of dhPRL but also intensify speculation as to its role in human gestation, including that related to osmoregulation across human amnion.