Vascular smooth muscle reactivity to norepinephrine in ovariectomized rats: Relationship to vascular PGE 2/PGF 2α ratio

Abstract

1. 1. We have recently demonstrated that, in normal female rats, vascular reactivity (VR) and vascular prostaglandin-E 2 (PGE 2) and prostacyclin production are influenced by the ovarian cycle. 2. 2. In this study, we investigated the vascular reactivity (VR) of isolated rat thoracic aorta to norepinephrine (NE 10 −12-10 −6M) in ovariectomized rats (OVX-rats), 48 hr and 8 days after surgical removal of the ovaries and in normally cycling rats (NR) at the proestrus stage of the estrous cycle, when the level of circulating estrogen was higher. 3. 3. In addition, we determined the vascular synthesis of PGE 2 and protaglandin-F 2α (PGF 2α) in both groups of OVX-rats, and in NR during the proestrous stage. 4. 4. The results showed that VR to NE 10 −12-10 −10 M was similar between OVX-rats and normal rats. 5. 5. However, aortic rings obtained from both groups of OVX-rats showed a significant increase of the contraction response induced by NE 10 −9-10 −6 M. 6. 6. Furthermore, the contractile response to NE 10 −7-10 −6 M was greater in the aortic rings from OVX-rats 8 days after ovariectomy compared to OVX-rats 48 hr ( p < 0.001). 7. 7. Vascular PGE 2 and PGF 2α synthesis (ng/mg protein/hr) was significantly higher in both groups of OVX-rats than NR. But the vascular PGF 2α synthesis increased more than PGE 2 in these OVX-rats, thus the ratio PGE 2/PGF 2α was decreased significantly in both groups of OVX-rats ( p < 0.01 and p < 0.001 OVX-rats 48 hr and 8 days after surgery, respectively) compared to NR-ratio.