Figure 1

Relaxin (R) administration increases serum R concentrations, which is enhanced by β-estradiol (E) and attenuated by progesterone (P). Systemic R concentrations were assayed in serum from sham-operated controls (SC), ovariectomized normal controls (NC), and rabbits treated with E, R, E + R (ER), P, P + R (PR), and E + P + R (EPR) groups on day 2 and day 6, respectively, using an enzyme-linked immunosorbent assay as described. (a) Histograms of the median with inter-quartile value showed that there was no statistically significant difference in the basal levels of R on day 2 between any of the groups. Additionally, the SC, NC, E, and P groups showed no statistically significant differences in R concentrations between day 2 and day 6. R administration resulted in a significant increase of systemic R concentration on day 6 in R, ER, PR, and EPR groups compared with the corresponding basal levels of R on day 2. (b) The fold change in R was determined by normalizing the day-6 concentration to the corresponding day-2 concentration of R for each animal, and the median with inter-quartile value was plotted for each group of animals. The fold increase in R was significantly greater in R (35-fold), ER (46-fold), PR (13-fold), and EPR (32-fold) groups compared with that in SC, NC, E, and P groups. No statistically significant difference of R ratio was found between any of the R-treated groups, with the exception of ER versus PR groups (p < 0.01). Data were collected from a minimum of six rabbits in each group and expressed as median with inter-quartile value. (* < 0.05; ** < 0.01; *** < 0.001; **** < 0.0001; a, versus SC; b, versus NC; c, versus E; d, versus P; e, versus PR.)