Expression of LGR7 in the primate corpus luteum implicates the corpus luteum as a relaxin target organ

Abstract

In women, the corpus luteum is the source of circulating relaxin. No previous studies have addressed whether the corpus luteum is also a relaxin target organ. We determined relaxin receptor LGR7 mRNA expression in human term pregnancy corpora lutea and nonhuman primate corpora lutea obtained during the menstrual cycle. Real-time reverse transcription-PCR demonstrated the expression of LGR7 mRNA in both human and rhesus monkey corpora lutea. Rhesus monkey corpora lutea were obtained from naturally cycling animals following documented luteinizing hormone (LH) surges at early, mid-, mid-late, and late luteal phases. Luteal expression of LGR7 mRNA did not show temporal variation. Since the primate corpus luteum is LH dependent, we assessed LGR7 mRNA expression in corpora lutea from rhesus monkeys treated with a gonadotropin-releasing hormone (GnRH) antagonist, which significantly suppressed pituitary LH levels. GnRH antagonist treatment, which also inhibits both progesterone and relaxin production, resulted in a fivefold increase in luteal LGR7 mRNA expression. These data suggest that luteal LGR7 mRNA expression may be regulated by relaxin and/or LH and that the primate corpus luteum is a target organ for relaxin.

Figure 1

LGR7 mRNA levels in corpora lutea obtained at various times during the luteal phase of the menstrual cycle. Corpora lutea are designated as early stage, (days 3-5), mid stage, (days 7-8), mid-late stage (days 10-11), and late stage (days 14-16) following a documented LH surge. Each bar represents the mean amount of LGR7 amplicon, (× 10^-5 attamoles ± standard error), resulting from total RNAs, obtained from 3 animals at each time point, that were reverse transcribed into cDNAs, each of which were subjected to 5 PCR reactions.

Figure 2

LGR7 mRNA levels (× 10^-5 attamoles ± standard error) in corpora lutea obtained from rhesus monkeys that were either untreated (controls n=3 animals) or received a GnRH antagonist, (3mg/kg) (n=3 animals) on days 6, 7, and 8 of the luteal phase of the menstrual cycle, to suppress pituitary LH. Corpora lutea were removed 24 hours later, on day 9. Data are expressed as described for Figure 1.

Figure 3

Expression of LGR7 mRNA in Human Term Pregnancy Corpora Lutea. Electrophoretic profiles of PCR products from reactions programmed by RNA isolated from 3 individual specimens (#1, #2, and #3) are shown. Lanes 1 and 20: 100 base pair DNA ladder. Lanes 2 and 3: Human CL #1, reactions with reverse transcriptase (RT). Lanes 4 and 5: Human CL #1, reactions without RT. Lanes 6 and 7: Human CL #2, reactions with RT. Lanes 8 and 9: Human CL #2, reactions without RT. Lanes 10 and 11: Human CL #3, reactions with RT. Lanes 12 and 13: Human CL #3, reactions without RT. Lanes 15, 16: Positive control with RT. Lane 17: Positive control without RT. Lane 18: Negative control with RT. Lane 19: Negative control without RT.