Neuropeptides such as vasoactive intestinal peptide, LHRH, or TRH have been found in rat pituitary tissue and could act via paracrine or autocrine actions in this tissue. In this study we investigated whether normal human pituitary tissue and GH-secreting human pituitary adenomas could release somatostatin (SRIH) and GHRH. Fragments from three human pituitaries and dispersed cells from six GH-secreting adenomas (four adenomas were studied for GHRH release and five for SRIH release) were perifused using a Krebs-Ringer culture medium, and the perifusion medium was collected every 2 min (1 mL/fraction for 5 h). GH, GHRH, and SRIH were measured by RIA under basal conditions and in the presence of 10(-6) mol/L TRH or SRIH. Both normal pituitaries and GH-secreting pituitary adenomas released SRIH and GHRH. SRIH release commenced 90-180 min after initiation of the perifusion, at which time GH secretion had decreased significantly. TRH stimulated SRIH release from normal pituitary tissue and inhibited SRIH release from adenoma tissue. GHRH was present at the start of the perifusion, but rapidly disappeared. However, SRIH stimulated GHRH release from normal pituitary tissue, but not from adenoma tissue. Significant amounts of GHRH and SRIH were released during the experiments, suggesting their local synthesis. These results indicate that pituitary cells can release hypothalamic peptides. The liberation of these neuropeptides is regulated, and moreover, their regulation differs between normal and adenomatous pituitaries.

Endogenous production of SRIH and GHRH was analyzed in human breast tissue. SRIH precursor (pro-SRIH) was identified after Sephadex G-50 filtration of acetic acid extracts of normal and tumoral human breast samples. SRIH-(1-14) or -(1-28) could not be detected in breast tissue, whereas the immunoreactive SRIH released in vitro was characterized as SRIH-(1-28). Endogenous production of GHRH was assessed by identification of GHRH messenger ribonucleic acid by PCR followed by sequencing of the amplified complementary DNA and by high performance liquid chromatographic characterization of immunoreactive GHRH contained in the tissue and released in vitro. There were no differences in pro-SRIH or GHRH-(1-44) tissue contents between normal and tumoral samples. The release of both peptides was evidenced in perifusion and static incubation. Perifusion of normal breast tissue (n = 3) showed pulsatile release of SRIH and GHRH. Perifusion of tumors (n = 4) showed SRIH release in 50% of the cases. SRIH release was pulsatile in one case. GHRH release was observed in the four tumoral samples analyzed, but was pulsatile in only one case. In static incubation, tumors (n = 6) secreted 13 times more GHRH than did normal samples (n = 3; 383 +/- 92 vs. 29.6 +/- 4.6 fmol/mg protein; P < 0.05). Stimulation of GHRH release by exogenous SRIH was observed only with the normal tissue. Together these data provide evidence for the existence of local production of SRIH and GHRH by human breast. Hypersecretion of GHRH by breast tumors indicates that this peptide could play a role in maintaining epithelial cell proliferation as is the case for other peptides produced locally.

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