Human prolactin heterogeneity in pituitary effluent blood

We have used column chromatography to study prolactin (PRL) heterogeneity in plasma obtained from the inferior petrosal vein, a sampling site very close to the anterior pituitary gland. Blood specimens were obtained from four hyperprolactinemic subjects over varying time intervals during inferior petrosal vein venography. All patients demonstrated an increase in PRL secretion during the sampling period which was presumably secondary to the mild stress of the procedure. In each study subject there was an increase in the percent and amount of PRL secreted as small PRL (peak III) as the PRL concentration in the inferior petrosal vein increased to a maximum. The percent secreted as intermediate PRL (peak II) fell while the amount either remained constant or increased slightly. The percent and amount eluting as large PRL (peak I) was small and unchanging in patients 1, 2 and 3, despite the increase in total PRL concentration. Patient 4 had an unusual elution pattern in which the 0 minute specimen contained predominantly large PRL. As the total PRL concentration increased the percent and amount eluting as small PRL dramatically increased while the percent eluting as large PRL fell in proportion to the increase of small PRL. Intermediate PRL was virtually absent in this patient. Thus, this study indicates that the increase in PRL concentration during a secretory pulse is primarily from small PRL while the contributions of large and intermediate PRL are modest and variable.