Metabolic Clearance Rate and Production Rate of 20α-Hydroxypregn-4-en-3-one in the Menstrual Cycle

Abstract

The metabolic clearance rate (MCR^r_B), plasma concentration, and production rate (P^I) and conversion to progesterone of 20Α-hydroxypregn-4-en-3-one (20Α-OHP) have been determined in women during the menstrual cycle. The MCR^r_B was 3,110 ± 217 (SE) 1/day and was independent of the day of the cycle. The P^I was 0.92–2.53 mg/day for days 6–18 of the cycle and 0.78–15.6 mg/day for days 20–24. The percent conversion of 20Α-OHP to progesterone was 4.88 ± 1.10 (SE)% and the calculated transfer constant of 20Α-OHP to progesterone was 0.05. The contribution of progesterone to the blood production rate of 20Α-OHP for days 20–24 was calculated to be between 24 and 73 %, and it was concluded that plasma concentrations of 20Α-OHP are not a valid indicator of corpus luteum regression in the human.

Progesterone: The Key Factor of the Beginning of Life

“…The per cent conversion of 20α-OHP to progesterone was 4.88 ± 1.10 (SE)% and the calculated transfer constant of 20α-OHP to progesterone was 0.05. The contribution of progesterone to the blood production rate of 20α-OHP on days 20-24 was between 24 and 73% [68]. The corpus luteum also secretes 5 alpha-pregnane-3,20dione (5 alpha-DHP) in an amount eightfold higher than in the follicular phase.…”

“…The production rate, which also depends on the MCR, defined as the volume of blood irreversibly cleared of a substance over time, which in turn supports the serum concentration [68]. Notably, the MCR of progesterone may change depending on exercise, body temperature, and other factors;…”

“…Metabolites in blood and tissue produced by progesterone vary depending on the route of administration, thereby inducing different effects on target tissues. For instance, the metabolism of oral progesterone differs from non-oral administration because of the first liver pass effect [68,[174][175][176] and the first uterine pass effect [112]. As a consequence, different routes of administration have different effects on endometrial pre-decidualization [112];…”