GRELİNİN YAPISI ve ORGANİZMADAKİ FONKSİYONLARI

Abstract

Grelin, 1999 yılında Masayasu Kojima tarafından tanımlanmış bir hormondur. 28 aminoasitten oluşmuş bir polipeptiddir. Dolaşımdaki grelin miktarının önemli bir kısmı mideden salgılanır ve biyolojik olarak aktif olabilmesi için üçüncü aminoasidi olan serin kalıntısına n-oktanoik asit bağlanması gereklidir. Grelin, reseptörü olan GHSR1a’a bağlanarak hücreiçi Ca konsantrasyonlarını arttırır, büyüme hormonu (GH) salgılanmasına neden olur ve birçok fizyolojik etkisini bu yolla gösterir. Grelin, hipotalamik arkuat nükleusa etki ederek, gıda alımını kontrol eder; açlıkta grelin düzeyleri yükselir, yemek yemeyi takiben düşer. Oreksijenik etkilidir ve leptine zıt etki gösterdiği bildirilmiştir. Açillenmemiş (n-oktanoik asit bağlanmamış) grelinin de biyolojik fonksiyonları olduğu düşünülmektedir; ancak henüz bağlandığı reseptör ve etki mekanizması tanımlanmamıştır. Açillenmemiş grelinin; hücre proliferasyonunda, lipolizde, adipogenezde ve kardivaskuler fonksiyonlarda etkili olduğu düşünülmektedir. Fizyolojik ve patolojik değişimlerde, grelin düzeylerinin azaldığı veya arttığı bildirilmiştir. Obezlerde ve tip 2 diyabetli kişilerde de grelin düzeylerinin düşük olduğu gösterilmiştir. Grelin salgılanması sirkadyen ritm gösterir; özellikle sabaha karşı 2 saatlerinde dolaşımdaki grelin miktarı en yüksek düzeydedir. Önümüzdeki dönemlerde yapılacak çalışmaların grelinin birçok bilinmeyen fonksiyonuna ve özellikle açillenmemiş grelinin biyolojik etkilerine ışık tutacağı düşünülmektedir.

Keywords

• Grelin, grelin yapısı, grelin fonksiyonları

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