Chen C, Farnworth P, Petersenn S, Musgrave I, Canny B J, Clarke I J
Prince Henry's Institute of Medical Research, Clayton, Victoria, Australia.
Endocrine. 1998 Aug;9(1):71-7. doi: 10.1385/ENDO:9:1:71.
Effect of growth hormone-releasing peptide-2 (GHRP-2) on ovine somatotrophs is abolished by a growth hormone-releasing factor (GRF) receptor antagonist, which raises the possibility that GHRP-2 may act on GRF receptors. In the present study, we used rat pituitary GC cells with or without stable transfection of cDNA coding for the human GRF receptor (GC/R+ or GC/R-) to determine whether or not GHRP-2 acts via the GRF receptor. Northern blot analysis indicated that GRF receptor mRNA was undetectable in GC/R-cells, whereas a high level of expression occurred in GC/R+ cells that were transfected by GRF receptor cDNA. In GC/R- cells, incubation with up to 10(-7)M of either hGRF or GHRP-2 did not alter the intracellular cAMP, [Ca2+]i, or GH secretion. In GC/R+ cells, hGRF (10(-11)-10(-7)M) increased cAMP levels in a concentration-dependent manner up to 20-fold. This increase in cAMP levels was blocked by a GRF receptor antagonist, [Ac-Tyr1, D-Arg2]-GRF 1-29, but not by a Ca2+ channel blocker, NiCl2 (0.5 mM). GH secretion and [Ca2+]i were, however, not increased by hGRF. Incubation of the transfected cells with 10(-1)-10(-8)MGH RP-2 did not modify intracellular cAMP levels. This result suggests that GHRP-2 does not act through the GRF receptor.
生长激素释放因子（GRF）受体拮抗剂可消除生长激素释放肽-2（GHRP-2）对绵羊生长激素分泌细胞的作用，这增加了GHRP-2可能作用于GRF受体的可能性。在本研究中，我们使用稳定转染了编码人GRF受体的cDNA的大鼠垂体GC细胞（GC/R+或GC/R-）来确定GHRP-2是否通过GRF受体发挥作用。Northern印迹分析表明，在GC/R-细胞中未检测到GRF受体mRNA，而在转染了GRF受体cDNA的GC/R+细胞中出现了高水平的表达。在GC/R-细胞中，用高达10^(-7)M的hGRF或GHRP-2孵育不会改变细胞内cAMP、[Ca2+]i或生长激素分泌。在GC/R+细胞中，hGRF（10^(-11)-10^(-7)M）以浓度依赖的方式将cAMP水平提高了20倍。cAMP水平的这种升高被GRF受体拮抗剂[Ac-Tyr1, D-Arg2]-GRF 1-29阻断，但未被Ca2+通道阻滞剂NiCl2（0.5 mM）阻断。然而，hGRF并未增加生长激素分泌和[Ca^2+]i。用10^(-1)-10^(-8)M GHRP-2孵育转染细胞不会改变细胞内cAMP水平。该结果表明GHRP-2不通过GRF受体发挥作用。
