Operational correlates of prostanoid TP receptor expression in human non-pregnant myometrium are unaffected by excision site or menstrual cycle status of the donor

1 Cumulative concentration-effect curves for the selective prostanoid TP receptor agonist, U46619, were constructed in strips of human non-pregnant myometrium grouped according to tissue excision site (top, lateral wall, lower uterine segment, sub-serosal or sub-endometrial), tissue orientation (strips cut either parallel or perpendicular to the serosa) and donor menstrual status (proliferative or secretory phase). 2 U46619 was excitatory in all tissues. There was no significant difference in either pEC(50) or maximum response between groups (P < 0.05). The range of pEC(50), values was 6.8 +/- 0.1 (lateral wall, proliferative phase, n = 5) to 7.1 +/- 0.3 (lateral wall, secretory phase, n = 5). The range of maximum response values was 0.9 +/- 0.8 N cm(-2) (lateral wall, proliferative phase, n = 5) to 3.1 +/- 1.0 N cm(-2) (lateral wall, secretory phase, it = 5). 3 Saturation binding analyses were conducted using the radiolabelled TP receptor agonist, [I-125]-BOP. Binding parameters were estimated for membranes prepared from human non-pregnant myometrium excised from the lateral wall and grouped according to donor menstrual status. 4 There were no significant differences in the mean pK(d) and [R](tot) values for [I-125]-BOP binding between the two groups (proliferative phase: pK(d) = 8.3 +/- 0.3, [R](tot) = 412 +/- 319 fmol mg protein(-1), n = 5; secretory phase: pK(d) = 8.5 +/- 0.4, [R](tot) = 369 +/- 192 fmol mg protein(-1), n = 6; P < 0.05). 5 These data indicate that U46619-mediated responses in human non-pregnant myometrium are not influenced by tissue excision site, tissue orientation or donor menstrual status and that [I-125]BOP binding is not influenced by donor menstrual status. This suggests that the TP receptor population is homogeneous throughout the human non-pregnant myometrium, and not subject to hormonal regulation.