Single and dual hormone secretors in GH3 cultures respond differently to hypothalamic factors

Recent studies using both normal and tumoral pituitary cell cultures have demonstrated that growth hormone (GH) and prolactin (PRL) secreting populations contain cells which release either one or both of these hormones. In order to determine whether these two cell types can be differentially regulated by hypothalamic factors we performed the following study employing plaque assays for GH and PRL. Using cultures of GH3 cells, a rat tumor cell line which contains both of these cell types, we found that the hypothalamic factors vasoactive intestinal peptide (VIP) and thyrotropin releasing hormone (TRH) when used together had a greater influence on plaque formation than when each was used individually. This suggested that cells were present in culture that responded to one peptide but not the other. Estradiol-treated cultures (which contain only dual-secreting cells) were then evaluated for VIP and TRH responsiveness and found to respond to TRH but not VIP. Finally, we assessed the peptide sensitivity of cultures that were exposed to a conjugate of VIP and the A-chain of ricin (a potent cytotoxin). In addition to eliminating VIP-responsive cells, this treatment markedly reduced the proportions of cells secreting GH-only while having no appreciable influence on dual-hormone secretors. When taken together, our findings indicate that single and dual secretors respond differently to at least two hypothalamic secretagogues and suggest that regulatory differences between these cell types may be important in the control of GH and PRL secretion.