Inhibition of nitric oxide synthase activity diminishes the acute effects of relaxin on growth, but not softening, of the cervix in the rat.

Relaxin promotes growth and softening of the cervix during pregnancy in the rat. This study examined the hypothesis that nitric oxide (NO) mediates the effects of relaxin on the rat cervix. To test that hypothesis, Nω-nitro-l-arginine methyl ester (L-NAME) was used to inhibit NO synthase, the enzyme that converts arginine to NO and l-citrulline. Nonpregnant rats were ovariectomized when they were 78 days old (day 1 of treatment). At ovariectomy each animal was fitted with silicon tubing implants containing progesterone (P) and estrogen (E) in doses that provide blood levels similar to those during late pregnancy. Rats were assigned to three treatment groups. The control group OPE (n = 6 rats) received 0.5 ml L-NAME vehicle (PBS) sc at 6-h intervals from 0600 h on day 7 through 1200 h on day 8 and 0.5 ml relaxin vehicle (PBS) sc at 0600 and 1200 h on day 8. Group OPER (n = 6 rats) was treated in the same way as group OPE, except that 20 μg porcine relaxin were administered. Group OPERI (n = 7 rats) was tre...