Journal of Applied Physiology, Vol 60, Issue 2 590-595, Copyright © 1986 by American Physiological Society
Progesterone receptors and ventilatory stimulation by progestin
P. Brodeur, M. Mockus, R. McCullough and L. G. Moore
Progestin is thought to be a ventilatory stimulant but its effectiveness in
raising ventilation is variable in humans and other species. We
hypothesized that the level of progesterone receptors was an important
determinant of the ventilatory response to progestin. Since estradiol
induces progesterone receptor formation, we compared the ventilatory effect
of the synthetic progestin medroxyprogesterone acetate (MPA) given in
combination with estradiol with the effects of estradiol alone, MPA alone,
or vehicle (saline) in ovariectomized rats. Animals receiving MPA alone had
low numbers of progesterone receptors (2.43 pmol/g uterine wt) and had no
change in ventilation, arterial Pco2, or Po2. MPA administration raised
ventilation 23 +/- 5%, lowered arterial Pco2 3.2 +/- 0.9 Torr (both P less
than 0.01) and tended to raise arterial Po2 when given in combination with
estradiol to animals with increased numbers of progesterone receptors (4.85
pmol/g uterine wt). Estradiol alone produced the highest number of
progesterone receptors (12.3 pmol/g uterine wt) but had no effect on
ventilation or arterial Pco2 and decreased arterial Po2. Combined estradiol
plus MPA treatment produced a greater fall in arterial Pco2 than did
treatment with MPA alone, estradiol, or saline (all P less than 0.05).
These results suggest that both an elevation in progestin levels and
progesterone receptor numbers are required to stimulate ventilation.
