In vivo pharmacological characterization of alpha adrenergic receptors in sheep myometrium and their physiological meaning.

Utero-cervical responsiveness to alpha-adrenergic receptor stimulation was electromyographically evaluated in vivo in adult ovariectomized ewes. Spontaneous motility and drug-induced changes were quantified with a microcomputer. Our results suggested that the two activity patterns previously described on the ovine genital tract could be respectively controlled by alpha-2 and alpha-1 adrenergic mechanisms. Alpha-2 receptors could be assigned to a chronotropic function by activating a hypothetical zone triggering the outbreak of discrete episodes of motility (regular activity); this function is apparent at the cervix even in the absence of estrogen priming. On the other hand, alpha-1 receptors could be assigned to an inotropic function, regulating mainly the magnitude of estrogen-dependent utero-cervical motility (irregular activity).