Alpha-Adrenergic Receptors in Myometrium of Pregnant and Nonpregnant Pigs Until Day 19 Postestrus

Binding of [3H] dihydroergocryptine (DHE) to myometrium was studied in cyclic and pregnant gilts. The binding was saturable and of high affinity (Kd = 2-4 nM). DHE binding was inhibited by phentolamine, phenoxybenzamine, epinephrine and norepinephrine, but almost not at all by propranolol or isoproterenol. DHE appears to be bound to an alpha 2-adrenergic receptor because yohimbine had a much greater ability to compete for DHE binding sites than did prazosin. The concentration of DHE binding sites in the myometrium was greatest during the luteal phase of the estrous cycle as has been previously reported for sheep. The decrease at estrus did not appear to be associated with a change in the alpha 2-adrenergic receptor dominance in myometrial membranes. Embryo migration to the site of implantation may be associated with reduced concentration of DHE binding sites on Days 10 to 12 of pregnancy in pigs.