Effect of pregnancy and steroid hormones on plasma adrenomedullin levels in the rat

Pregnancy is characterized by volumeexpansion and vasodilation. We investigated whether thehypotensive peptide adrenomedullin (ADM) might be a significantfactor in the cardiovascular adaptation to pregnancy. Rats wereprepared with indwelling cannulae. Plasma ADM levels weremeasured by RIA before mating, at 7, 14, and 21 days ofpregnancy, and at 7 days postpartum. We also investigated theeffects on plasma ADM levels of administering estrogen,progesterone, and the metabolite of progesterone3-OH-5-pregnan-20-one(3-OH-DHP); this last steroid has been implicated inaltering reflex control of blood pressure and volume duringpregnancy. Plasma ADM levels increased progressively duringpregnancy from 123 ± 27 pg/mL in virgin animals to 404 ± 50 pg/mLat 21 days of pregnancy. The levels returned to pre-pregnancyvalues postpartum.3-OH-DHP caused a significant rise in plasma ADM levels,whereas neither estrogen nor progesterone had any effect. Wesuggest that ADM may be an important contributing factor to thevasodilatatio...