In vitro effects of L-arginine on spontaneous and homocysteine-induced contractility of pregnant canine uteri

The L-Arginine-Nitric Oxide Synthase-Nitric Oxide (L-Arg-NOS-NO) system exerts a pivotal role in the maintenance of uterine quiescence during pregnancy, whereas Homocysteine (Hcy) promotes uterine contractility. The aim of this study was to test the in vitro effects of L-Arg on spontaneous and Hcy-induced contractions of uteri excised from pregnant bitches. 104 strips cut from pregnant uteri were mounted in an organ bath. 40 out of 104 strips (16 from mid-gestation uteri and 24 from close to term uteri, respectively) were exposed to cumulative doses of L-Arg; 40 strips (16 from mid-gestation-uteri and 24 from close to term-uteri, respectively) were exposed to N-nitro-L-arginine methyl ester (L-NAME), a NOS antagonist; the remaining 24 strips (from close-to-term uteri) were first exposed to a single dose of Hcy and then to increasing doses of L-Arg. L-Arg showed no effects on spontaneous contractility both in mid-gestation- and close to term-uterine strips, whereas it promoted a relaxant effect on Hcy-induced contractility. On the contrary, L-NAME increased amplitude of contraction both in mid-gestation and close to term strips. These findings suggest that the L-Arg-NO system is present in the uterus of pregnant bitches and that Hcy is able to modulate its actions. Further investigation of this system may provide the basis of future obstetrical therapies in bitches.