Beyin (Hipotalamus, Hipofiz) ve Polikistik Over Sendromu

Beyinde hipotalamus bölgesinde GnRH (Gonadotropin-releasing hormone) salgılayan sinir hücreleri (neurons) bulunmaktadır(1,2). GnRH hormonunun belirli aralıklarla artışlar ve azalışlar gösterek (pulsatile) salgılanmasına bağlı olarak hipofiz bezinde LH ve FSH hormonların üretim sıklığı (frequency) ve miktarları (amplitude) belirlenmektedir(3,4,5). Polikistik over sendromu olan kadınların bir kısmında GnRH hormonu salgılayan jeneratörün (dinamo) beyinde fazla çalışmasına (hyperactive) bağlı olarak GnRH hormonunun belirli aralıklarla (pulsatile) salgılanma sıklığında artış görülmektedir. Bunun sonucunda polikistik over sendromu olan kadınların bir kısmında hipofiz bezinde LH hormonunun üretim sıklığı (frequency), miktarı (amplitude) ve kan dolaşımında bulunan (basal) miktarı artmaktadır(3,5,6,7,8,9,10,11,12) Erkeklik hormonlarının yumurtalıkta yapılmasını sağlayan LH (luteinizing hormon) miktarının artması erkeklik hormonlarının yapımını arttırmakla (hiperandrogenism) birlikte yumurtlama öncesi olgun folikül (dominant) gelişimini ve yumurtlamayı (ovulasyon) da engellemektedir(5,12,13,14,15,16,17,18,19,20,21,22).

Polikistik over sendromu olan kadınların bir kısmında GnRH hormonu salgılayan jeneratörün (dinamo) fazla çalışmasına (hyperactive) neden olan beyinde daha üst seviyelerde bulunan sinir hücreleri (neurons) vardır(23,24,25,26,27,28,29). Bu sinir hücrelerinden GABA ve Kisspeptin (neurotransmitters) salgılanmaktadır. Kisspeptin salgılayan sinir hücrelerinin bir kısmından Neurokinin B (NKB) ve Dynorphin (neurotransmitters) de salgılanmaktadır(29,30,31,32,33,34,35). Bu maddeler (neurotransmitters) polikistik over sendromu olan kadınlarda hipofiz bezinde üretilen LH hormonu miktarı ile birlikte salgılanma zamanının sıklığını (frequency) da arttırmaktadır(23,24,25,26,27,28,29,30,31,32,36,37,38,39,40).

Polikistik over sendromu olan kadınların bir kısmında erkeklik hormonlarının (testosteron, dihidrotestosteron) fazla miktarda üretilmesi (hyperandrogenism) ve insülin direncine bağlı insülin miktarının artması (hyperinsulinemia) beyinde GnRH hormonu salgılayan jeneratörün (dinamo) fazla çalışmasına (hyperactive) neden olmaktadır(24,26,41,42). Erkeklik hormonları (testosteron, dihidrotestosteron) ve insülin bunu GnRH (Gonadotropin-releasing hormone) salgılayan sinir hücrelerinden (neurons) daha üst seviyelerdeki sinir hücrelerinde üretilen GABA ve Kisspeptin (neurotransmitters) salgılanmasını etkileyerek yapmaktadır(3,26,41,42).

Kaynaklar

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13-Estradiol production by granulosa cells of normal and polycystic ovaries: relationship to menstrual cycle history and concentrations of gonadotropins and sex steroids in follicular fluid. Mason HD, Willis DS, Beard RW, Winston RM, Margara R, Franks S. J Clin Endocrinol Metab. 1994 Nov;79(5):1355-60.

14-Premature response to luteinizing hormone of granulosa cells from anovulatory women with polycystic ovary syndrome: relevance to mechanism of anovulation. Willis DS, Watson H, Mason HD, Galea R, Brincat M, Franks S. J Clin Endocrinol Metab. 1998 Nov;83(11):3984-91.

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23-Activation of A-type gamma-aminobutyric acid receptors excites gonadotropin-releasing hormone neurons. DeFazio RA, Heger S, Ojeda SR, Moenter SM. Mol Endocrinol. 2002 Dec;16(12):2872-91.

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26-Kisspeptins and reproduction: physiological roles and regulatory mechanisms. Pinilla L, Aguilar E, Dieguez C, Millar RP, Tena-Sempere M. Physiol Rev. 2012 Jul;92(3):1235-316.

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