Relaxin on Induction of Parturition in Beef Heifers*

Abstract

Purified porcine relaxin (3000 U/mg) was administered into the cervical os of primiparous beef heifers on day 278 of gestation (approximately 5 days before parturition normally occurs) to determine its effects on the induction of parturition, changes in progesterone, estrone (E1), 17 beta-estradiol (17 beta-E2), cervical dilation, and pelvic relaxation. Heifers were assigned randomly to 1 of 3 treatments: relaxin-double (two infusions of 3000 U, 12 h apart; n = 17), relaxin-single (3000 U; n = 14), and PBS-gel vehicle (n = 16). Relaxin induced marked earlier calving (P less than 0.002) than PBS-gel vehicle. The intervals between the administration of relaxin or the PBS-gel vehicle and calving were 2.0, 2.5, and 5.3 days for heifers given relaxin-double, relaxin-single, and PBS-gel vehicle, respectively. The duration of gestation was significantly reduced (P less than 0.002) in relaxin-treated heifers compared with that in control heifers. A precipitous decrease in progesterone (7.1 ng/ml) occurred in peripheral blood plasma within 24 h after relaxin treatment. Coincident with a decline in levels of progesterone, E1 and 17 beta-E2 increased by 1700 and 400 pg/ml, respectively, an increase of 35% compared with the 12% increase in these steroids in control heifers. Mean deviations of cervical dilation increased 643%, 526%, and 11% in heifers given relaxin-double, relaxin-single, and PBS-gel vehicle, respectively. Relaxin induced maximum pelvic opening between 12-36 h after treatment. Although relaxin induced significantly earlier calving, there was no incidence (0 of 31 heifers) of retained placenta. We conclude from this study that purified relaxin administered intracervically to primiparous beef heifers during late pregnancy induced premature parturition. Marked shifts of progesterone, E1, 17 beta-E2, pelvic canal expansion, and cervical relaxation reflect the premature parturition induced by relaxin.

Relaxin Activates the l -Arginine–Nitric Oxide Pathway in Vascular Smooth Muscle Cells in Culture

“…30 The choice of VSMCs of bovine origin was motivated by the fact that these cells retain a distinct muscular phenotype in in vitro culture, including the ability to produce NO, 30 and that porcine RLX has been found to be active in cattle heifers in vivo. 50 Smooth muscle tissue strips were explanted from bovine aortas and placed in tissue-culture flasks. The tissue strips were then incubated in DMEM plus 10% FCS until the SMCs, which had spread from the explants, reached confluence.…”

Relaxin on induction of parturition in cattle: effects on hormonal, pelvic and cervical changes, and postpartum fertility

“…The combined induction resulted in reduced intervals between drug treatment and calving, shortened the calving period, reduced the incidence and severity of dystocia, reduced the proportion of heifers with retained placenta as well as the duration of retained placenta. These events were preceded by an accelerated decrease of plasma progesterone, and pelvic and cervical relaxation in much the same manner as reported earlier (Musah et al, 1986a,b).In this study, the profile of plasma peripheral progesterone levels during the periparturient period was similar to those observed during the periparturient period associated with normal calving, relaxin facilitated calving, prostaglandin or glucocorticoid induced calving (Johnson and Jackson, 1982;Musah et al, 1986a). Relaxin alone or combined with cloprostenol and dexamethasone is associated with luteal demise, consistent with earlier reports (Musah et al, 1986a).…”

“…This study indicates that a combined treatment of relaxin with cloprostenol or dexamethasone reduced the incidence and severity of dystocia due to increased cervica^. and pelvic relaxation (Musah et al, 1986b) as well as reduced the incidence of retained placenta as reported earlier (Musah et al, 1986a).The mechanisms by which relaxin may reduce retained placenta are unknown* The maternal and fetal connective tissue in placentome becomes progressively collagenized up to the time of parturition. At the onset of parturition, the tissue of the placentome becomes loose, a process that is essential for expulsion of the fetal membranes (Grunert, 1980).…”

“…The results in the present study indicate that pelvic growth during the last 10 days before parturition can be modified by the intracervical administration of relaxin. Apart from modifying these pelvic parameters, the administration of relaxin at this time significantly reduces the duration of gestation by inducing earlier calving (Musah et al, 1985). The mean interval between the administration of relaxin or eel-vehicle and calving was 2.1.…”

“…The inter-assay and intra-assay variabilities for progesterone were determined from replicates of a peripheral serum pool from mid-gestation sham-operated heifers. The inter-assay and intra-assay coefficients of variation were 7.2% (n=3) and 4.1% (n=6), respectively.Concentrations of E^ and I76-E2 in peripheral blood plasma were quantified as described previously by Musah et al (1986a). Recovery after extraction was 85-95% and 86-95% for and respectively=…”