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. 1995 Aug;115(7):1211–1214. doi: 10.1111/j.1476-5381.1995.tb15027.x

Increased sensitivity of rat myometrium to the contractile effect of platelet activating factor before delivery.

B K Kim 1, H Ozaki 1, S M Lee 1, H Karaki 1
PMCID: PMC1908802  PMID: 7582547

Abstract

1. The contractile effects of platelet activating factor (PAF) were compared in the myometrium isolated from non-pregnant and pregnant rats. 2. In the non-pregnant myometrium, PAF, at a concentration of 0.1 microM, did not change muscle tension and induced only a small transient contraction at 10 microM. 3. The contractile responses to PAF increased with the progress of gestation. In the late pregnant myometrium (21 day after gestation), PAF (0.1 nM-10 microM) induced large and relatively sustained contractions. The threshold concentration of PAF was decreased by approximately 10,000 times and the maximum contraction was increased 5 times by day 21 of gestation. 4. PAF (10 microM) increased the cytosolic Ca2+ concentration ([Ca2+]i) and muscle contraction to levels higher than those induced by high K+ in the pregnant rat myometrium (day 21). Verapamil (10 microM), a voltage-dependent Ca2+ channel blocker, decreased the stimulated [Ca2+]i and muscle tension to 49.6% and 22.7%, respectively, while the same concentration of verapamil completely inhibited the high K(+)-induced responses. 5. PAF (10 microM) induced a transient increase in [Ca2+]i with no contraction in the absence of external Ca2+ in the pregnant myometrium (day 21). 6. These results suggest that PAF induces contraction in rat myometrium by increasing Ca2+ influx. Although PAF released Ca2+ from stored sites, this Ca2+ does not seem to contribute to the PAF-induced contraction. Our major finding is that the sensitivity of the myometrium to PAF increased after gestation and that this may play a role in delivery.

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Selected References

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