Ghrelin对雏鸵鸟腺胃和小肠生长发育的作用及其机制研究

Ghrelin, a novel peptide isolated from stomach tissue of rats and humans, has been identified as the endogenous ligand for the growth hormone secretagogue receptor (GHS-R). The African ostrich is the biggest herbivorous bird in the world, and it has longer brood time.During the brood time, due to the development of digestive system is not perfect and the digestive ability is poor, thus affecting its growth. The previous test result indicated that the expression of Ghrelin mRNA and distribution of Ghrelin-immunopositive cells in the gastrointestinal tract of African ostriches changes with age, it is the most obvious change in the proventriculus and small intestine, these results suggest that ghrelin may be involved in gastrointestinal tract development, but the effect and its mechanism of action between them has not been verified. So, in the present study, in order to study the effect and its mechanism of action between ghrelin and the process of growth and development in the proventriculus and small intestine of the African ostrich chicks , after injection of ostrich Ghrelin homologue in the African ostrich chicks ，the Genome-wide expression, distribution of Ghrelin-immunopositive cells and its receptor, the content of GH in plasma, the content of SS and gastrin in the tissue , the process of growth and development of the proventriculus and small intestine were investigated from the level of genes, subcellsular level, hormone level, cell and tissue level. These results will offer the theoretical basis for further understanding the physiological functions of Ghrelin in the gastrointestinal tract of the poultry; Also provide a new research idea for how to accelerate the development of digestive tube, improve the digestive capacity and production performance in the African ostrich chicks. Therefore it has important theoretical significance and potential application value .

Ghrelin是一种脑肠肽，主要由胃内分泌细胞分泌，是生长激素促分泌素受体的一种特定的内源性配体。非洲鸵鸟是体型最大的草食型鸟，育雏期长，在育雏期间由于消化系统发育不完善而导致其消化能力较差，影响其生长。前期试验结果发现: Ghrelin阳性细胞及 mRNA在鸵鸟消化道的分布和表达都随着雏鸵鸟年龄变化而变化，其中腺胃和小肠的变化最明显，暗示Ghrelin与雏鸵鸟消化管的生长发育有一定的关系。但究竟有何关系及其作用机制如何，却未能探明。本课题拟以雏鸵鸟为研究对象，通过注射鸵鸟Ghrelin的同源物，从基因水平、亚细胞水平、激素水平、细胞和组织水平开展Ghrelin对雏鸵鸟腺胃和小肠生长发育的作用及其机制研究，其研究结果将对深入了解Ghrelin与禽类胃肠道的生理功能提供理论依据；也为加快雏鸵鸟消化管的发育完善，提高其消化能力及生产性能提供新的研究思路，因此具有重要的理论意义和潜在的应用价值。

为了探明外源性Ghrelin与雏鸵鸟腺胃和小肠的生长发育关系，本研究通过皮下静脉注射和跖静脉注射不同浓度的Ghrelin后，采用多种方法研究外周注射Ghrelin对雏鸵鸟腺胃和小肠生长变化的影响，其结果显示：1.当颈部皮下注射和跖静脉注射不同浓度的ghrelin后，非洲雏鸵鸟的摄食量和饮水量都增加，但体重变化不明显。2. 一定剂量Ghrelin能够促进腺胃重量的增加，小肠长度的增加；促进腺胃和小肠黏膜层、黏膜下层、肌层和浆膜层的厚度。3. 一定剂量Ghrelin能够促进腺胃和小肠Ghrelin免疫阳性细胞和的生长抑素阳性细胞的增加。4. 不同浓度ghrelin使雏鸵鸟血液中生长激素和胃泌素的含量增加，使腺胃和小肠中胃泌素、胃蛋白酶的含量也均有增加。以上结果说明，ghrelin通过促进鸵鸟的摄食、饮水、胃蛋白酶的活性、胃泌素的分泌、生长激素的分泌、ghrelin及抑制生长抑素的表达来促进雏鸵鸟腺胃和小肠的生长发育。这些结果为Ghrelin与禽类胃肠道的生理功能提供了理论依据，也为加快雏鸵鸟消化管的发育完善，提高其消化能力及生产性能提供新的研究思路。另外，本课题也进行了采用免疫组化法对ghrelin在非洲鸵鸟的其它组织中的分布定位进行了研究，其结果显示：ghrelin阳性细胞在非洲鸵鸟胰腺的胰岛及腺泡细胞中均有分布，且在胰岛中分布较多，腺泡细胞中分布较少，且随着鸵鸟年龄的增加其表达量逐步减少；Ghrelin阳性细胞在鸵鸟肝脏的枯否氏细胞和肝窦内皮细胞均有分布，而在肝细胞和肝门区均无分布；Ghrelin阳性细胞在鸵鸟胸腺皮质和髓质中均有表达，尤其是在上皮细胞和胸腺小体中，而胸腺细胞内未检测到阳性细胞；Ghrelin阳性细胞位于肺部三级支气管之间的粘膜上皮细胞、呼吸毛细血管上皮细胞和巨噬细胞中；Ghrelin免疫阳性细胞在非洲鸵鸟睾丸曲精小管的精原细胞、初级精母细胞、精细胞、精子、Leydig细胞、肌样细胞、支持细胞以及间质组织中均有分布；Ghrelin 阳性细胞分布于除包膜外的整个肾上腺，大部分ghrelin 阳性细胞位于嗜铬细胞中；以上结果说明，ghrelin对非洲鸵鸟其它组织器官的发育也有一定影响。