Luque R M, Rodríguez-Pacheco F, Tena-Sempere M, Gracia-Navarro F, Malagón M M, Castaño J P
Department of Cell Biology, Physiology and Immunology, University of Córdoba, Córdoba, Spain.
J Neuroendocrinol. 2005 Sep;17(9):577-82. doi: 10.1111/j.1365-2826.2005.01345.x.
There is increasing evidence that nitric oxide (NO) produced by NO synthase (NOS), and their signalling partners, guanylyl cyclase and cGMP, play a relevant role in growth hormone (GH) secretion from somatotrophs. We previously demonstrated that both GH-releasing hormone (GHRH; 10(-8) M) and low concentrations of somatostatin (10(-15) M) stimulate pig GH release in vitro, whereas a high somatostatin concentration (10(-7) M) inhibits GHRH-induced GH secretion. To ascertain the possible contribution of the NOS-NO and guanylyl cyclase-cGMP routes to these responses, cultures of pituitary cells from prepubertal female pigs were treated (30 min) with GHRH (10(-8) M) or somatostatin (10(-7) or 10(-15) M) in the absence or presence of activators or blockers of key steps of these signalling cascades, and GH release was measured. Two distinct activators of NO route, SNAP (5x10(-4) M) or L-AME (10(-3) M), similarly stimulated GH release when applied alone (with this effect being blocked by 10(-7) M somatostatin), but did not alter the stimulatory effect of GHRH or 10(-15) M somatostatin. Conversely, two NO pathway inhibitors, NAME (10(-5) M) or haemoglobin (20 microg/ml) similarly blocked GHRH- or 10(-15) M somatostatin-stimulated GH release. 8-Br-cGMP (10(-8) to 10(-4) M) strongly stimulated GH release, suggesting that cGMP may function as a subsequent step in the NO pathway in this system. Interestingly, 10(-7) M somatostatin did not inhibit the stimulatory effect of 8-Br-cGMP. Moreover, although 8-Br-cGMP did not modify the effect of GHRH, it enhanced GH release stimulated by 10(-15) M somatostatin. Accordingly, a specific guanylyl cyclase inhibitor, LY-83, 583 (10(-5) M) did not alter 10(-15) M somatostatin-induced GH release, whereas it blocked GHRH-induced GH secretion. These results demonstrate for the first time that the NOS/NO signalling pathway contributes critically to the stimulatory effects of both GHRH and low-concentration somatostatin on GH release, and that, conversely, the subsequent guanylyl cyclase/cGMP step only mediates GHRH- and not low-concentration somatostatin-induced GH secretion from somatotrophs.
越来越多的证据表明，一氧化氮合酶（NOS）产生的一氧化氮（NO）及其信号转导伙伴鸟苷酸环化酶和环磷酸鸟苷（cGMP）在生长激素细胞分泌生长激素（GH）过程中发挥着重要作用。我们之前证明，生长激素释放激素（GHRH；10⁻⁸ M）和低浓度的生长抑素（10⁻¹⁵ M）均可在体外刺激猪GH释放，而高浓度的生长抑素（10⁻⁷ M）则抑制GHRH诱导的GH分泌。为了确定NOS-NO和鸟苷酸环化酶-cGMP途径对这些反应的可能贡献，将青春期前雌性猪的垂体细胞培养物在不存在或存在这些信号级联关键步骤的激活剂或阻滞剂的情况下，用GHRH（10⁻⁸ M）或生长抑素（10⁻⁷或10⁻¹⁵ M）处理（30分钟），并测量GH释放。两种不同的NO途径激活剂，硝普钠（SNAP；5×10⁻⁴ M）或L-精氨酸甲酯（L-AME；10⁻³ M）单独应用时同样刺激GH释放（这种作用被10⁻⁷ M生长抑素阻断），但不改变GHRH或10⁻¹⁵ M生长抑素的刺激作用。相反，两种NO途径抑制剂，Nⁿ-甲基-L-精氨酸（NAME；10⁻⁵ M）或血红蛋白（2 μg/ml）同样阻断GHRH或10⁻¹⁵ M生长抑素刺激的GH释放。8-溴环磷酸鸟苷（8-Br-cGMP；10⁻⁸至10⁻⁴ M）强烈刺激GH释放，表明cGMP可能在该系统的NO途径中作为后续步骤发挥作用。有趣的是，10⁻⁷ M生长抑素并不抑制8-Br-cGMP的刺激作用。此外，尽管8-Br-cGMP不改变GHRH的作用，但它增强了10⁻¹⁵ M生长抑素刺激的GH释放。因此，一种特异性鸟苷酸环化酶抑制剂，LY-83,583（1⁻⁵ M）不改变10⁻¹⁵ M生长抑素诱导的GH释放，而它阻断GHRH诱导的GH分泌。这些结果首次证明，NOS/NO信号通路对GHRH和低浓度生长抑素刺激GH释放的作用至关重要，相反，随后的鸟苷酸环化酶/cGMP步骤仅介导GHRH而非低浓度生长抑素诱导的生长激素细胞GH分泌。
