Csapo, A. I. (1956). Progesterone block. The American Journal of Anatomy, 98(2), 273-291. https://doi.org/10.1002/aja.1000980206
Csapo AI. Progesterone block. Am J Anat. 1956;98(2):273-291. doi:10.1002/aja.1000980206
Csapo, Arpad. "Progesterone block." The American Journal of Anatomy, vol. 98, no. 2, 1956, pp. 273-291.
For EndNote, Zotero or Mendeley:
License
Open-access status not yet checked.
RRM Academy Synopsis
Progesterone blocks organized uterine contractions in pregnant rabbits
In rabbits, progesterone blocks pregnant uterine muscle from contracting until labor starts, a 1956 review of experiments argues. The author proposes a similar block in other species as a working hypothesis. He links the block to low potassium and high sodium in muscle cells. These levels block excitation but do not change the muscle's working capacity.
Study at a glance, 1956 review article: Progesterone blocks pregnant uterine muscle contractions in rabbits. Source: Csapo AI, 1956, PMID 13326855.
Key Findings
The uterine contractile system, actomyosin-ATP, was not noticeably different under estrogen and progesterone domination, so the author placed the progesterone effect higher in the excitation-contraction process.
Horvath found a lower potassium to sodium ratio inside uterine muscle cells under progesterone domination than under estrogen domination.
In rabbits, oxytocin did not induce labor before day 30 of pregnancy. Twenty-four hours later, 96% of the rabbits went into labor and delivered when given oxytocin.
With progesterone prolonging pregnancy in more than 900 fetuses, live birth averaged 96% until day 32, fell after that, and reached zero by the 36th day.
In rabbit tests that the author says need extension, uterine muscle nearest a placenta showed stronger progesterone domination than muscle between two placentas or in the non-pregnant horn.
Interpretation
This is a 1956 review article. The author summarizes earlier work on the corpus luteum. He also describes experiments from his own lab, mostly in rabbits, including uterine strips studied in a laboratory dish. He extends the progesterone block to humans, monkeys, and other species as a working hypothesis. Potassium and sodium findings from his group support this idea. The author notes that proving the hypothesis in other species will need more experimental data. The findings support further study of progesterone's role across species and of the timing of progesterone therapy.
RRM Context
Many doctors doubted progesterone's role in human pregnancy after repeated failures of replacement therapy. This review calls that doubt unjustified. In rabbits, the progesterone effect took 12 to 24 hours to show up. The author says this may mean human progesterone therapy needs a fresh look at timing and dose. NaProTechnology protocols use cycle-timed progesterone support guided by charting.
Our editorial summary of this paper, not the article's abstract.
