AUTOCRINE AND PARACRINE EFFECTS OF PEPTIDES ON HUMAN PITUITARY-CELLS

In contrast to normal human pituitaries, GH-secreting adenomas cannot process in vivo ProSRIH whereas they do it in vitro. The existence of an endogenous factor able to inhibit ProSRIH processing in vivo was po stulated and such a role was analyzed for GHRH. Results showed that wh en GH adenomas are incubated in vitro with GHRH 10(-8)M, their ProSRIH contents are decreased, percent inhibition being negatively correlate d to the amount of endogenously released GHRH. When incubation is perf ormed in the presence of GHRH antibody in order to block the effect of endogenous GHRH, ProSRIH content is increased. The same effects are o bserved on SRIH release: inhibition by GHRH, stimulation by GHRH antib ody. Normal rabbit serum had no effect. It may therefore be concluded that the absence of ProSRIH maturation observed in adenomas in vivo ma y be the consequence of the GHRH release that is known to be higher fr om GH adenomas than from normal pituitaries.