Oestrous cycle and pregnancy alter the reactivity of the rat uterine vasculature

Isolated uterine vascular beds from virgin and pregnant rats were used to a ssess vascular reactivity and the ability of nitric oxide (NO), prostanoids and endothelium-derived hyperpolarizing factor (EDHF) to modulate these re sponses. One uterine horn from female rats in each oestrous cycle day and g estation day 17 was removed and perfused with physiological saline solution . Tone was induced with cirazoline (1 mu mol/l), and concentration-response curves to acetylcholine (ACh) generated. Responsiveness to ACh was tested in the presence of N-nitro-L-arginine (L-NA), ibuprofen (IBU) and tetrabuty lammonium (TBA), to inhibit NO synthase, cyclo-oxygenase and K+ channels re spectively. Cirazoline-induced tone was smaller in the pregnant compared wi th the proestrous group. Sensitivity to ACh was cycle day and pregnancy dep endent with pregnant > dioestrous day-1 > dioestrous day-2 > proestrous and oestrous. L-NA shifted the curve to the right in all groups except dioestr ous day-1. IBU inhibited the ACh response in the pregnant group only. TBA v irtually abolished the response in all groups. These results suggest that i n the uterine vascular bed from pregnant rats, EDHF, along with NO and a di lator prostanoid mediate ACh-induced dilatation, In contrast, in the dioest rous day-1 group, only EDHF seems to be released by ACh in this vascular be d. Lu the oestrous, dioestrous day-2 and proestrous groups, ACh releases bo th EDHF and NO.