Chen C, Pullar M, Loneragan K, Zhang J, Clarke I J
Prince Henry's Institute of Medical Research, Clayton, Victoria, Australia.
J Neuroendocrinol. 1998 Jun;10(6):473-80. doi: 10.1046/j.1365-2826.1998.00233.x.
There is a difference between the sheep and rat somatotrophs in the response to growth hormone-releasing peptide-2 (GHRP-2), which raises the question of what the response may be in human somatotrophs. In the present study, cells were obtained from seven human acromegalic tumours and the effects of GHRP-2 were studied. Cells were dissociated and kept in primary culture for 1-3 weeks before experimentation. Application of GHRP-2 for 30 min induced a significant increase in GH secretion from the cultured cells from all seven tumours whereas human GH-releasing hormone (hGHRH) at a dose of 10 nM induced a significant GH release in only four of seven tumours. The intracellular levels of cAMP in all seven tumours were significantly increased by both 10 nM GHRP-2 and GHRH, but the response to GHRH was significantly higher than the response to GHRP-2. The adenylyl cyclase inhibitor, MDL 12330A, blocked the effect of GHRH and GHRP-2 on intracellular cAMP levels, whereas the Ca2+ channel blocker Co2+ (0.5 mM) did not attenuate the cAMP response. For the tumours in which GH secretion was increased by GHRH and GHRP-2, the cAMP antagonist Rp-cAMP blocked the GH response to GHRH but not to GHRP-2. When a protein kinase A (PKA) inhibitor (H89) was applied, GHRH stimulated GH release was blocked, but cAMP accumulation was not affected. The response to GHRP-2 was not altered by H89. Calphostin C [a protein kinase C (PKC) inhibitor] reduced the effect of GHRP-2 on the secretion of GH but did not affect the response to GHRH. Both GHRH and GHRP-2 increased the intracellular Ca2+ concentration in a concentration-dependent manner. We conclude that (1) GHRH increases GH secretion from human GH tumours via the cAMP pathway whereas GHRP-2 increases GH secretion mainly via the PKC pathway; (2) GHRH increases cAMP (without GH release) in a subset of tumours whereas GHRP-2 increases cAMP levels (slightly) and GH secretion in all tumours; and (3) GHRP-2 and GHRH do not act on the same receptor on human somatotrophs derived from acromegalic tumours.
绵羊和大鼠的生长激素细胞对生长激素释放肽-2（GHRP-2）的反应存在差异，这就引出了人类生长激素细胞的反应可能是什么的问题。在本研究中，从7例人类肢端肥大症肿瘤中获取细胞，并研究了GHRP-2的作用。在实验前，将细胞解离并进行原代培养1 - 3周。应用GHRP-2 30分钟可使所有7个肿瘤的培养细胞中生长激素（GH）分泌显著增加，而10 nM剂量的人类生长激素释放激素（hGHRH）仅在7个肿瘤中的4个中诱导出显著的GH释放。10 nM GHRP-2和GHRH均使所有7个肿瘤中的细胞内cAMP水平显著升高，但对GHRH的反应显著高于对GHRP-2的反应。腺苷酸环化酶抑制剂MDL 12330A可阻断GHRH和GHRP-2对细胞内cAMP水平的影响，而Ca2+通道阻滞剂Co2+（0.5 mM）并未减弱cAMP反应。对于GHRH和GHRP-2能增加GH分泌的肿瘤，cAMP拮抗剂Rp-cAMP可阻断GH对GHRH的反应，但不能阻断对GHRP-2的反应。当应用蛋白激酶A（PKA）抑制剂（H89）时，GHRH刺激的GH释放被阻断，但cAMP积累不受影响。H89未改变对GHRP-2的反应。钙泊三醇C [一种蛋白激酶C（PKC）抑制剂]降低了GHRP-2对GH分泌的作用，但不影响对GHRH的反应。GHRH和GHRP-2均以浓度依赖的方式增加细胞内Ca2+浓度。我们得出结论：（1）GHRH通过cAMP途径增加人类GH肿瘤中的GH分泌，而GHRP-2主要通过PKC途径增加GH分泌；（2）GHRH在一部分肿瘤中增加cAMP（不伴有GH释放），而GHRP-2在所有肿瘤中均增加cAMP水平（轻微）和GH分泌；（3）GHRP-2和GHRH对源自肢端肥大症肿瘤的人类生长激素细胞的作用并非作用于同一受体。
