Abstract-Hypertension and vascular dysfunction result in the increased release of endothelium-derived contracting factors (EDCFs), whose identity is poorly defined. We tested the hypothesis that endothelial cyclooxygenase (COX)-2 can generate EDCFs and identified the possible EDCF candidate. Changes in isometric tension of aortae of young and aged hamsters were recorded on myograph. Real-time changes in intracellular calcium concentrations ([Ca 2ϩ ] i ) in native aortic endothelial cells were measured by imaging. Endothelium-dependent contractions were triggered by acetylcholine (ACh) after inhibition of nitric oxide production and they were abolished by COX-2 but not COX-1 inhibitors or by thromboxane-prostanoid receptor antagonists. 2-Aminoethoxydiphenyl borate (cation channel blocker) eliminated endothelium-dependent contractions and ACh-stimulated rises in endothelial cell [Ca 2ϩ ] i . RT-PCR and Western blotting showed COX-2 expression mainly in the endothelium. Enzyme immunoassay and high-performance liquid chromatography-coupled mass spectrometry showed release of prostaglandin (PG)F 2␣ and prostacyclin (PGI 2 ) increased by ACh; only PGF 2␣ caused contraction at relevant concentrations. COX-2 expression, ACh-stimulated contractions, and vascular sensitivity to PGF 2␣ were augmented in aortae from aged hamsters. Human renal arteries also showed thromboxane-prostanoid receptor-mediated ACh-or PGF 2␣ -induced contractions and COX-2-dependent release of PGF 2␣ . The present study demonstrates that PGF 2␣ , derived from COX-2, which is localized primarily in the endothelium, is the most likely EDCF underlying endothelium-dependent, thromboxane-prostanoid receptor-mediated contractions to ACh in hamster aortae. These contractions involved increases in endothelial cell [Ca 2ϩ ] i . The results support a critical role of COX-2 in endothelium-dependent contractions in this species with an increased importance during aging and, possibly, a similar relevance in humans. Key Words: endothelium-derived contracting factors Ⅲ cyclooxygenase-2 Ⅲ thromboxane-prostanoid receptor Ⅲ aging Ⅲ aorta B esides neuronal and hormonal regulation, vascular tone is modulated locally by a delicate balance between endothelium-derived relaxing (EDRFs) and contracting (EDCFs) factors, 1,2 with the latter being less well-defined but emerging in hypertension, obesity, hyperlipidemia, diabetes, and aging. 3 A number of molecules have been proposed as possible EDCF candidates under pathophysiological conditions. These include prostaglandin (PG)H 2 , thromboxane (TX)A 2 , leukotrienes, endothelin 1, and superoxide anions. The release of these tentative EDCFs can be triggered by acetylcholine (ACh), angiotensins I/II, ADP, and ATP. 4 The contribution of additional cyclooxygenase (COX)-derived metabolites, ie, PGE 2 , PGD 2 , and PGF 2␣ , has been postulated. The precise nature of these EDCFs varies among species and vascular beds. 1,3 Two isoforms of COX have been identified in blood vessels. COX-1 is constitutively expressed and...

Aims: The role of endothelium-derived contracting factors (EDCFs) in regulating renovascular function is yet to be elucidated in renovascular hypertension (RH). The current study investigated whether oxidative stressdependent cyclooxygenase (COX)-2-derived prostaglandin F 2a (PGF 2a ) impairs endothelial function in renal arteries of renovascular hypertensive rats (RHR). Results: Renal hypertension was induced in rats by renal artery stenosis of both kidneys using the 2-kidney 2-clip model. Acute treatment with reactive oxygen species (ROS) scavengers, COX-2 inhibitors, and thromboxane-prostanoid receptor antagonists, but not COX-1 inhibitors, improved endothelium-dependent relaxations and eliminated endothelium-dependent contractions in RHR renal arteries. Five weeks of treatment with celecoxib or tempol reduced blood pressure, increased renal blood flow, and restored endothelial function in RHRs. Increased ROS production in RHR arteries was inhibited by ROS scavengers, but unaffected by COX-2 inhibitors; whereas increased PGF 2a release was reduced by both ROS scavengers and COX-2 inhibitors. ROS also induced COX-2-dependent contraction in RHR renal arteries, which was accompanied by the release of COX-2-derived PGF 2a . Further, chronic tempol treatment reduced COX-2 and BMP4 upregulation, p38MAPK phosphorylation, and the nitrotyrosine level in RHR renal arteries. Conclusion: These findings demonstrate the functional importance of oxidative stress, which serves as an initiator of increased COX-2 activity, and that COX-2-derived PGF 2a plays an important role in mediating endothelial dysfunction in RH. Innovation: The current study, thus, suggests that drugs targeting oxidative stress-dependent COX-2-derived PGF 2a may be useful in the prevention and management of RH .

The mechanisms that underlie progestogen-induced endometrial breakthrough bleeding are poorly understood. The aim of the present study was to quantify endometrial microvascular density in 54 controls and 42 women with 3-12 months' exposure to Norplant (levonorgestrel subdermal contraceptive implant) and to correlate it with bleeding pattern, endometrial histology, and peripheral plasma oestradiol and progesterone concentrations. Endometrial biopsies were processed routinely and sections immunostained using anti-CD34 antibody to identify vascular endothelial cells. Menstrual record card data were analysed using World Health Organization definitions. The mean microvascular density (+/- SEM) for control samples was 186 +/- 8 vessels/mm2, and there were no significant differences across the cycle. Norplant user's endometrial microvascular density was significantly elevated above controls (294 +/- 18 vessels/mm2, P = 3.36 x 10(-8)). Endometrial microvascular density in Norplant users did not correlate with oestrogen concentrations prior to biopsy, bleeding patterns or endometrial histology. The results from this study show that women receiving Norplant have significantly increased endometrial microvascular density compared to controls. Another finding from this study was that bleeding in Norplant users often occurred from thin atrophic endometrium. These results provide new insights into the physiological mechanisms that may be involved in progestogen-induced endometrial bleeding.

SUMMARY1. Acid secretion by the rat cauda epididymidis was studied by microperfusion of the epididymal duct and by measuring the pH of the perfusate at a constant pCO2 using a micro pH sensitive electrode. The rate of acidification was expressed as the rate of fall of intraluminal bicarbonate per cm duct per min.2. When the cauda epididymal duct was perfused with normal bicarbonate solution, the luminal bicarbonate concentration fell at a rate of 0-59 + 0-39 n-equiv cm-1 min-(mean + S.E., n = 22).3. The rate of luminal acidification was independent of the perfusion rate but was dependent on the concentration of bicarbonate in the perfusion fluid. The rate of fall of luminal bicarbonate increased with increasing bicarbonate concentration and showed saturation at an intraluminal bicarbonate concentration of 25 m-mole/l.4. Acidification was abolished in the absence of intraluminal sodium ions. This may suggest a linked sodium reabsorption and hydrogen ion secretion.5. Acidification of the luminal fluid was studied under different acid-base conditions. In animals undergoing metabolic acidosis, the rate of acidification was enhanced, and conversely in animals undergoing metabolic alkalosis, the rate was depressed.6. Intravenous infusion of acetazolamide into rats at a dose rate of 20 mg/kg. hr markedly inhibited the acidification process. This effect was still observed in animals undergoing metabolic acidosis. Acetazolamide (10-5 M) applied luminally was found to have no effect but higher concentration (10-4 M) was found to inhibit acidification by 50 %.7. The role of acidification of the epididymal fluid in sperm maturation was discussed.