Effects of Several Sera on Prolactin and GH Release from Rat Pituitary Cells in Vitro

Abstract

Abstract

To study the acute effects of serum and albumin on prolactin (PRL) and growth hormone (GH) release from pituitary cells, 10, 25, and 50% of normal rat (NRS), horse (HS), fetal calf (FCS), or normal human serum (NHS) or 1, 2.5, and 5% of bovine serum albumin (BSA) was administered to dispersed rat pituitary cells (DC) and to clonal rat pituitary mammotrophs (2B8). Further, to obtain information on the nature of the serum factors influencing pituitary hormone release TRH or serum from hypophysectomized rats or heated, or dialyzed rat serum was also added into the culture medium containing DC, or 2B8 cells. Twenty-five and fifty percent of NRS, HS, and NHS consistently stimulated PRL and GH release from DC cultures. In contrast, FCS and BSA had no effect on the release of either hormone. 2B8 cells showed significant increases in the release of PRL during incubation with NRS, HS, NHS, or FCS at all of the concentrations of serum employed. However, the 2B8 cells showed no change in PRL release when BSA was added to the culture medium. The PRL and GH releasing activities of 10^-7 M TRH or 25% of hypophysectomized rat serum were much smaller than those obtained with the addition of 25% NRS to DC or 2B8 cells. Moreover, dialysis of NRS (which removes molecules below a mol wt of 12,000) significantly reduced the releasing activities for PRL both in DC and 2B8 cultures, while heat treatment of NRS did not change the activities in either cell system. These results indicate that (i) mammalian sera possess PRL- and GH-releasing activities, (ii) TRH is probably not a factor in this response although other hypothalamic releasing or release-inhibiting hormones may be involved, and (iii) these factors are heat stable and some of the PRL-releasing factors are molecules below a mol wt of 12,000.