The direct effects of progesterone/progestin on vascular tone

Cho, Soo Hyun; Kim, Seung Ryong; Kim, Kyoung Hun; Suh, Jung Kook

Abstract

OBJECTIVES
To evaluate the effects of progesterone/progestin and in combination with estrogen in relaxation of rat aorta.
METHODS
Eight weeks after bilateral oophorectomy, the descending aorta of Spague-Dawley rats (n=10) were quickly removed and placed in organ bath containing Krebs solution. Each aorta ring in 2-3 mm length was connected to an isometric force transducer (FT 03, Grass, USA) and the changes in tension were recorded with an AD converter system (MP 100, Biopac Inc, USA) in a personal computer. After precontraction of the rings with norepinephrine (1 umol/L) or KCl (40 mmol/L), estradiol, progesterone, medroxyprogesterone acetate (MPA), norethisterone acetate (NETA) (10-5-10-8 M/L in each) were added to each ring and they were incubated for 15 minutes. The relaxation was expressed as a percentage of the tonic contraction.
RESULTS
Estrogen relax the aorta in all concentrations. The degree of relaxation was dose dependent (P<0.001). All of the progesterone, MPA, NETA relax the aorta and the effects was different according to the concentration of steroids (P<0.0001). The degree of relaxation was not different between estrogen and those of progesterone, MPA, NETA except MPA 10-8 M, NETA 10-5 M. Addition of progesterone, MPA and NETA to the estrogen showed similar vascular effects compared to those of estrogen alone.
CONCLUSION
Not only estrogen but also progesterone, MPA, and NETA acutely relax aorta. Progesterone/progestin have not been found attenuate the action of estrogen in our animal in vitro study.