lects the significant increase in PTGS2 and the terminal prostanoid synthases AKR1B1, CBR1 and PTGES3. The immuno-localization of CBR1, AKR1C3 and AKR1B1 are predominantly in the glandular epithelium and vasculature of the endometrium. This is in agreement with previous studies which report glandular epithelial cells to produce more PGF2a than stromal cells. AKR1C3 immunoreactivity has previously been shown in the luminal and glandular epithelium. We also demonstrate AKR1B1 immunoreactivity in a subset of stromal cells in the late and menstrual phases. Immunostaining for AKR1B1 localized to the perinuclear region in stromal cells. Terminal prostanoid synthases show distinct functional coupling with upstream COX G5555 site isoxymes. The immunostaining supports previous data suggesting that AKR1B1 couples to PTGS2 which resides predominantly in the perinuclear membranes. PGI2 is the main prostanoid synthesized by the vascular endothelium and it causes blood vessel dilatation and inhibition of platelet aggregation: these effects have suggested a role for PGI2 in menstruation. PTGIS and PTGIR immunoreactivity in the endometrium is localized predominantly to the glandular and luminal epithelium with expression also detected in the vasculature and stroma. PGI2 has been shown to be inhibited by progesterone which correlates with the expression of PGIS peaking in the late secretory phase as progesterone is withdrawn. PTGIR with a similar expression profile has also been demonstrated to be inhibited by progesterone as expression increases in the endometrium after administration of mifepristone. This study represents the first comprehensive view of prostanoid action in the endometrium during the menstrual cycle. Identifying the expression profile of the prostanoid system and its association to PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19817327 key inflammatory events provides valuable insight into the role of specific signalling pathways in normal endometrial function. Menstrual cycle disorders such as primary dysmenorrhea and heavy menstrual blood loss in the absence of any pathology have been associated with an increase and an imbalance in prostanoid synthesis. Hence the data presented herein provides the potential to identify which component of the prostanoid system may contribute to Expression profiles of the prostanoid system in the endometrium 191 induced progesterone withdrawal reveals novel regulatory pathways in human endometrium. The secretin receptor-like family B and metabotropic glutamate receptor-like family C were directly subjected to these methods. Conclusions: Our trees show the overall relationship of 277 GPCRs with emphasis on orphan receptors. Support values are given for each branch. This approach may prove valuable for identification of the natural ligands of orphan receptors as their relation to receptors with known ligands becomes more evident. refereed research interactions Background G-protein-coupled receptors are the largest and most diverse family of transmembrane receptors. They respond to a wide range of stimuli including small peptides, lipid analogs, 
amino-acid derivatives, and sensory stimuli such as light, taste and odor, and transmit signals to the interior of the cell through interaction with heterotrimeric G proteins. Certain amino-acid residues of this receptor family are well conserved and approaches exploiting this, such as low-stringency hybridization and degenerate PCR, have been used to clone new members of this large superfamily. Many of these putative receptor