Characterization of "big big prolactin" in serum and tumor extract in patients with PRL-secreting tumor.

Molecular size heterogeneity of immunoreactive prolactin (PRL) in sera of pregnant women and patients with PRL-secreting pituitary tumor as well as pituitary tumor extract was investigated. "Big big PRL" in the vicinity of the void volume was identified by PRL radioimmunoassay. The ratio of "big big PRL" to "little PRL" was almost constant in normal pregnant women, while the proportion varied from case to case in patients with pituitary tumor. The ratio of "big big PRL" to "little PRL" was significantly (P less than 0.01) larger in these patients (43.3 +/- 9.8%, mean +/- SE) than in pregnant women (13.0 +/- 0.77%). Neither radiation therapy nor thyrotropin releasing hormone (TRH) stimulation significantly affected the ratio of "big big PRL" to "little PRL", while it decreased from 20.5% to 9.5% one month after tumor resection. The elution patterns of the normal human pituitary extract and the tumor extract obtained from patients with PRL-secreting pituitary tumor revealed peaks in identical positions, although the ratio of "big big PRL" to "little PRL" in the tumor extract (38.2 +/- 3.6%) was significantly (P less than 0.01) larger than that in normal human pituitary extract (5.8 +/- 2.8%). These results indicate that "big big PRL" is present in sera of pregnant women and patients with PRL-secreting pituitary tumor, normal pituitary extract and tumor extract. It is also suggested that the increased circulating "big big PRL" observed in patients with PRL-secreting tumor may originate in tumor tissue.