Relaxin acts centrally to inhibit XXXX release during parturition: an effect that is reversed by @entity1510 .

@entity35 @entity398 @entity1510
Experiments were carried out to establish whether infusion of relaxin prolongs gestation and labour in the @entity35 by suppressing release of @entity398 , and whether the effects of relaxin on birth could be reversed by the opioid antagonist @entity1510 . Female @entity35 were implanted with subcutaneous osmotic minipumps for the infusion of purified porcine relaxin into the jugular vein for 84 h from either day 19 or day 20 of gestation. Infusion of relaxin delayed the onset of labour and in those animals which delivered during relaxin infusion, delivery was longer by approximately 45 min. Plasma @entity398 levels 40 min after delivery of the first fetus were 45.25 +/- 3.6 pmol/l (mean +/- S.D.) in unoperated controls and significantly (P less than 0.01) depressed (23.89 +/- 3.9) in @entity35 that delivered during infusion of relaxin. @entity35 that delivered after the infusion of relaxin had finished, gave birth significantly (P less than 0.05) faster than controls and plasma @entity398 levels were significantly (P less than 0.01) raised (77.87 +/- 15.9 pmol/l). @entity1510 treatment (1 mg/kg; i.m.) given immediately after the delivery of the first fetus reversed the inhibitory effect of relaxin and the interval between successive deliveries was slightly faster than that of controls. Plasma @entity398 levels in relaxin-infused @entity1510 -treated @entity35 were significantly (P less than 0.01) higher than values in unoperated control @entity35 . The results confirm that relaxin suppresses @entity398 release possibly through an opioid system and this may be important in the control of the timing of birth.
