Serum Immunoreactive Relaxin and Softening of the Uterine Cervix in Pregnant Hamsters

Abstract

Serum immunoreactive relaxin levels and ripening of the cervix were measured throughout pregnancy in hamsters. RIA relaxin rose from an undetectable level on day 7 to a maximum value of 29 ng/ml on day 15 of gestation and then fell prior to parturition. The cervix became progressively more dilatable from the 12th to the 16th day of pregnancy. It is suggested that the endogenous relaxin measured by RIA may induce the cervical softening. The absolute levels of immunoreactive relaxin appear to be 10 to 15-fold higher than those previously observed in rats, mice and guinea pigs.

The effects of oestradiol benzoate, progesterone, relaxin and ovariectomy on cervical extensibility in the late pregnant rat

“…Serum relaxin concentrations in pregnant rats, as measured by radioimmunoassay, reach a peak about Day 15 and then slowly decline . This peak precedes the rise in cervical extensibility in rats and there is some correspondence between serum relaxin concen¬ trations and increased cervical size in the pregnant hamster (O'Bryne, Sawyer, Butler & Steinetz, 1976). Ovariectomy would remove the source of relaxin in the rat and this could explain the minimal increase in cervical extensibility in the ovariectomized, steroid-treated group.…”

The Role of Placental Hormones in Mediating Maternal Adaptations to Support Pregnancy and Lactation

“…In pregnant women, circulating relaxin concentration peaks in the first trimester, declines in the second trimester and is maintained until delivery in the third trimester (Quagliarello et al, 1979 ; Seki et al, 1985 ). In contrast, circulating relaxin peaks toward term in mice, rats, guinea pigs and hamsters (O'byrne and Steinetz, 1976 ; O'byrne et al, 1976 ; Renegar and Owens, 2002 ). In pregnant mice, relaxin deficiency leads to proteinuria, suggesting a particular role of relaxin in modulating renal function during pregnancy (O'sullivan et al, 2017 ).…”

“…In mice with a deficiency in relaxin signaling, obstructed deliveries occur at a higher rate due to poor maturation of the cervix (Zhao et al, 1999 ; Kamat et al, 2004 ; Krajnc-Franken et al, 2004 ; Kaftanovskaya et al, 2015 ). Conversely in hamsters, the rise in circulating relaxin toward term coincides with cervical ripening in preparation for delivery (O'byrne et al, 1976 ). Insufficient relaxin signaling also impedes mammary development through excessive duct dilation and reduces the nursing of offspring in mice (Zhao et al, 1999 ; Kamat et al, 2004 ; Krajnc-Franken et al, 2004 ).…”

Relaxin as a New Hormone*

“…Interestingly, there was no significant correlation in the same Winter, 1982 RELAXIN 77 animal between the changes in the cervix and the changes in the interpubic ligament, suggesting that each tissue has a different priming optimum. Serum relaxin immunoactivity measured in a porcine relaxin RIA has been shown to correlate with cervical softening during pregnancy in the hamster (125).…”