Reproductive biology and endocrinology : RB&EDec 9, 2004

Effects of 17alpha-hydroxyprogesterone caproate (17P) on human uterine muscle contractions in the lab

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Apr 2, 2026

Abstract

There was no significant direct effect of 17 alpha-hydroxyprogesterone caproate (17P) on myometrial contractility in either pregnant or non-pregnant human tissues.

Spontaneous contractions in pregnant myometrium showed a mean maximal inhibition of 4.9% with 17P treatment.
Oxytocin-induced contractions in pregnant myometrium had a mean maximal inhibition of 2.2% with 17P treatment.
In non-pregnant myometrium, spontaneous contractions had a mean maximal inhibition of 8.8% with 17P treatment.
Phenylephrine-induced contractions in non-pregnant myometrium exhibited a mean maximal inhibition of -7.9% with 17P treatment.
The lack of significant direct effects suggests that potential benefits of 17P in preventing preterm labor may rely on genomic mechanisms rather than immediate utero-relaxant effects.

Simplified

BACKGROUND: 17 alpha-hydroxyprogesterone caproate (17P) administration reportedly improves outcome for women with a previous spontaneous preterm delivery. This study, using in vitro strips of human uterine smooth muscle, aimed to investigate the direct non-genomic effects of 17P on spontaneous and induced contractions in tissues obtained during pregnancy, and in the non-pregnant state.

METHODS: Biopsies of human myometrium were obtained at elective cesarean section, and from hysterectomy specimens, and dissected strips suspended for isometric recordings. The effects of 17P (1 nmol/L -10 micro mol/L) on spontaneous and agonist-induced (oxytocin 0.5 nmol/L for pregnant, phenylephrine 10 micromol/L for non-pregnant) contractions were measured. Integrals of contractile activity, including the mean maximal inhibition values (MMI) observed at the maximal concentration, were compared with those from simultaneously run control strips.

RESULTS: There was no significant direct effect exerted by 17P on pregnant or non-pregnant human myometrial contractility. The MMI +/- SEM for spontaneous contractions in pregnant myometrium was 4.9% +/- 7.2 (n = 6; P = 0.309) and for oxytocin-induced contractions was 2.2% +/- 1.3 (n = 6; P = 0.128). For non-pregnant myometrium, the MMI +/- SEM for spontaneous contractions was 8.8% +/- 11.0 (n = 6; P = 0.121) and for phenylephrine induced contractions was -7.9% +/- 6.5 (n = 6; P = 0.966).

CONCLUSIONS: The putative benefits of 17P for preterm labor prevention are not achieved, even partially, by a direct utero-relaxant effect. These findings outline the possibility that genomic effects of 17P, achieved over long periods of administration, are required for its reported therapeutic benefits.

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Effects of 17alpha-hydroxyprogesterone caproate (17P) on human uterine muscle contractions in the lab

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