Mechanism of the haemotensive action of porcine relaxin in anaesthetized rats.

Abstract Experiments were done to examine the pressor effect of iv porcine relaxin in anaesthetized rats. Acute injections of relaxin caused consistent and sustained rises in systemic blood pressure that were dose-dependent within the physiological range. Pretreatment of rats with a specific vasopressin (V1) receptor antagonist, but not an alpha-adrenoreceptor antagonist, substantially reduced the pressor effect of relaxin. After the vasopressin receptor antagonist, small rises in blood pressure occurred after a longer latent period, compared with the responses in intact animals. The data clearly indicate that acute injections of relaxin cause a pressor response that is predominantly affected via the release of vasopressin. The possible sources of the persistent hypertensive component are discussed and it is suggested that relaxin might act through the central angiotensinergic systems to release vasopressin and cause a pressor response.