Effects of growth hormone-releasing factor(1–44) on growth hormone release from human somatotrophinomas in vitro: interaction with somatostatin, dopamine, vasoactive intestinal peptide and cycloheximide

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Abstract
The effect of GH-releasing factor(1–44) (GRF) alone, or together with somatostatin (SRIF), dopamine (DA), vasoactive intestinal peptide (VIP) or cycloheximide was studied in a total of ten human somatotrophinomas using a static cell culture system. Growth hormone-releasing factor (2·0×10−8 mol/l) significantly (P−10−2·0×10−8 mol/l) was observed in five tumours thus studied. Repeated GRF (2·0×10−8 mol/l)-mediated GH release was seen during 96% (n = 25) of experiments performed on six tumours over 4 h and up to 27 days in culture. Growth hormone-releasing factor (2·0×10−8 mol/l) also stimulated GH release from five out of seven somatotrophinomas during 60-min incubations. Somatostatin (6·1×10−9 mol/l) completely inhibited GRF-induced GH secretion from four tumours studied over 4 h, but in each case there was significant (PP< 0·01) enhanced GRF-stimulated release of GH during a 60-min incubation, but inhibited both basal and GRF-stimulated release over 4 and 8 h. We conclude that a static cell culture system can be used successfully to study the action of GRF on human somatotrophinoma tissue for up to 27 days in culture. Human somatotrophinomas seem to be only rarely unresponsive to the stimulatory action of GRF, which is itself significantly modulated by SRIF, DA and VIP. De-novo protein synthesis appears to be necessary for the full expression of GRF activity on human somatotrophinoma tissue. J. Endocr. (1985) 105, 269–276

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