We examined if rat myometrial cells in culture generate nitric oxide (
NO) and express various isoforms of NO synthase (NOS), Myometrial cell
s isolated from rats on day 18 of gestation were incubated with variou
s stimulators and inhibitors of NOS for 24 and 48 h, and NO production
was evaluated by measuring nitrites in the media and NOS proteins in
the cell lysates. NO was produced by myometrial cells and its producti
on inhibited by N-G-methyl-L-arginine (L-NMMA), This inhibition was re
versed by L-arginine (3 mM). Interleukin-1 beta (IL-1 beta) significan
tly stimulated NO production, in a dose-dependent manner, The IL-1 bet
a-stimulated NO production was inhibited by the NOS inhibitor, L-NMMA,
whose effects were reversed by L-arginine. Abundant NOS III protein w
as detectable in freshly isolated myometrial cells, and this was maint
ained in culture in the presence of fetal bovine serum (FBS; 10%). In
the absence of FBS, NOS III levels decreased significantly (by 90%) wi
thin 24 h. In contrast, NOS I and NOS II proteins were undetectable in
freshly isolated muscle cells and in cells cultured without IL-1 beta
, However, NOS II protein in these cells was induced by IL-1 beta. Thu
s, NO is produced by myometrial cells through the NOS III isoform, and
the myometrial NO may be important in maintaining uterine quiescence
during pregnancy.