EFFECTS OF RELAXIN ON BLOOD-PRESSURE AND THE RELEASE OF VASOPRESSIN AND OXYTOCIN IN ANESTHETIZED RATS DURING PREGNANCY AND LACTATION

The effects of porcine relaxin (pRXN) on arterial blood pressure and o n the release of vasopressin (VP) and oxytocin (OT) were investigated in urethane-anesthetized rats at different stages of pregnancy and lac tation. Acute i.v. pRXN (5 mu g) caused a significant increase in syst olic and diastolic blood pressure in pregnant and lactating rats. Howe ver, the presser response was attenuated from Day 14 of pregnancy to D ay 1 of lactation. The hormone had no effect on blood pressure in Day 16, Day 19, or Day 21 pregnant rats. At all stages of pregnancy and la ctation, i.v. pRXN caused a significant increase in plasma VP concentr ations. This response was attenuated in Day 19 and Day 21 pregnant and in Day 1 lactating rats. intravenous pRXN also caused a significant, short-term increase in plasma OT in pregnant and lactating rats. The O T response to pRXN was attenuated on Day 16 of pregnancy, and pRXN had no effect on plasma OT in late-pregnant rats. The data in this study demonstrate that pRXN causes an increase in both arterial blood pressu re and VP and OT release in anesthetized pregnant and lactating rats. However, these effects are either reduced or not observed in late-preg nant and early-lactating rats.