Somatostatin receptor 2 expression in the human endometrium through the menstrual cycle

Abstract

Somatostatin mediates its many inhibitory functions through five G-protein-coupled receptors (sstr1-5); however, it is not known whether somatostatin or its receptors are present in the endometrium. We have used immunohistochemistry on formalin-fixed paraffin-embedded sections of normal human endometrium from the menstrual (n = 6), proliferative (n = 15) and secretory (n = 10) stages of the endometrial cycle to determine the pattern of expression of somatostatin receptor (sstr) subtype 2. In addition, we have used quantitative polymerase chain reaction (PCR) to determine the level of expression of the sstr2 mRNA in 17 samples of normal human endometrium. Endometrial tissue had been removed from patients undergoing dilation and curettage (D&C) for menorrhagia and had been determined to be normal histologically. Immunostaining in the epithelium, endothelium and the stroma of the endometrial sections was characterized and was scored positive or negative. The PCR results were analysed using the software provided to standardize the expression of sstr2 against that of constitutively expressed beta-glucoronidase in the same sample. A final percentage value of the level of sstr2 expression was then determined. sstr2 was expressed variably throughout all the stages of the menstrual cycle in the epithelium, the endothelium and the stroma. In particular, the position of sstr2 expression varied in the epithelial cells surrounding the endometrial glands from being basal or diffuse in the proliferative and secretory phase to being lumenal in the menstrual stage. Quantitative PCR showed that 15 of 17 samples expressed sstr2 mRNA and the level of expression between individual samples varied dramatically. These data show that sstr2 is present in the endometrium and its location seems to vary through the menstrual cycle.