The role of endothelium in phenylephrine- and potassium-induced contractions of the rat aorta during pregnancy

Disrupting effects of the emerging contaminant octylmethoxycinnamate (OMC) on human umbilical artery relaxation

Cardiovascular diseases (CVD) represent the number one cause of death worldwide. The vascular endothelium may play a role in the pathophysiology of CVD diseases. Octylmethoxycinnamate (OMC) is a UV-B filter (CAS number: 5466-77-3) widely used worldwide in numerous personal care products, including sunscreens, daily creams, and makeup. This UV-B filter is considered an endocrine disruptor. Therefore, this investigation aimed to evaluate the direct effects of OMC in human umbilical arteries (HUAs) with endothelium and the possible mechanisms involved in the response. The results demonstrated that OMC exerts a rapid (non-genomic) and endothelium-dependent arterial relaxant effect on HUAs previously contracted with serotonin (5-HT) and Histamine (His). On the other hand, when HUAs were contracted with potassium chloride (KCl), the relaxing effect was only observed in HUAs without endothelium, and it appeared to be inhibited in HUAs with endothelium. Thus, the vasorelaxant effect of OMC depends on the endothelium and depends on the contractile agent used, suggesting that OMC may act through different signaling pathways. Furthermore, computational modulation studies, corroborated the binding of OMC to all the proteins under investigation (eNOS, COX-2, ET-1, and TxA2), with higher affinity for COX-2. In summary, the vascular effect of OMC may involve activating different pathways, i.e., acting through the NO pathway, COX pathway, or activating the endothelin-1 pathway.

Endothelium-dependent relaxation and angiotensin II sensitivity in experimental preeclampsia

Objective

We investigated endothelial dysfunction and the role of angiotensin (Ang)-II type I (AT1-R) and type II (AT2-R) receptor in the changes in the Ang-II sensitivity in experimental preeclampsia in the rat.

Methods

Aortic rings were isolated from low dose lipopolysaccharide (LPS) infused pregnant rats (experimental preeclampsia; n=9), saline-infused pregnant rats (n=8), and saline (n=8) and LPS (n=8) infused non-pregnant rats. Endothelium-dependent acetylcholine--mediated relaxation was studied in phenylephrine-preconstricted aortic rings in the presence of vehicle, N^G-nitro-L-arginine methyl ester and/or indomethacin. To evaluate the role for AT1-R and AT2-R in Ang-II sensitivity, full concentration response curves were obtained for Ang-II in the presence of losartan or PD123319. mRNA expression of the AT1-R and AT2-R, eNOS and iNOS, COX1 and COX2 in aorta were evaluated using real-time RT-PCR.

Results

The role of vasodilator prostaglandins in the aorta was increased and the role of endothelium-derived hyperpolarizing factor and response of the AT1-R and AT2-R to Ang-II was decreased in pregnant saline infused rats as compared with non-pregnant rats. These changes were not observed during preeclampsia.

Conclusion

Pregnancy induced adaptations in endothelial function, which were not observed in the rat model for preeclampsia. This role of lack of pregnancy induced endothelial adaptation in the pathophysiology of experimental preeclampsia needs further investigation.

The alterations of vascular smooth muscle reactivity in vitro by human chorionic gonadotrophin

The study tests the hypothesis that human chorionic gonadotrophin (hCG) alters vascular smooth muscle reactivity by examining the effect of hCG administration on the contractility and relaxation of isolated vascular smooth muscle. Aortic rings from rats pre-treated with intraperitoneal administration of 5,000 I.U of hCG and control animals were contracted to phenylephrine, angiotensin II, CaCl2 and KCl. The experiments with phenylephrine were repeated with rings that were either de-endothelialized, incubated with L-NMMA, or incubated with calcium ionophore A23187. Aortic rings precontracted with phenylephrine were relaxed to acetylcholine (endothelium-dependent), sodium nitroprusside, hydralazine (endothelium-independent) or in the presence of A23187. The contractile responses of aortic rings from hCG-treated animals of phenylephrine, angiotensin II, CaCl2 and KCl were significantly attenuated. This effect was not reversed by pre-treatment with L-NMMA or by de-endothelialisation. In aortic rings from hCG-treated animals, there was almost total inhibition of acetylcholine-induced relaxation, but unaltered relaxation responses to sodium nitroprusside and hydralazine. The inhibitory effects of hCG-treatment on both the contraction and relaxation responses were either fully or partially reversed in the presence of calcium ionophore A23187. These observations suggest that hCG attenuates both contractile and endothelium-dependent relaxation responses by a mechanism which involves inhibition of extracellular calcium ion influx and may indicate a new role for the hormone in the altered vascular responses of both normal and abnormal pregnancies.

A variation in acetylcholine-induced relaxation of rat aorta in pregnancy

The tension of isolated ring preparations of the thoracic aortae from pregnant rats on Days 7, 14, and 21 was measured isometrically to study the effect of advancing pregnant stage on endothelium-dependent relaxing factor activity. The endothelium-dependent relaxation caused by acetylcholine (ACh) (10(-8) - 3x10(-5) M) in the aortae of pregnant rats on Days 7, 14, and 21 were greater than that in those of diestrus (D-2) rats. In pregnant rats, the endothelium-dependent relaxation caused by acetylcholine was greatest in the aortae from pregnant rats on Day 21. In contrast with ACh, the relaxation caused by sodium nitroprusside was decreased in the aortae from pregnant rats on Day 21, compared with metestrus (D-1) and estrus (E) rats. The peaks of serum estradiol and progesterone levels in pregnant rats were observed on Days 21 and 14, respectively. These results suggest that there is a fluctuation of endothelium-dependent relaxing factor activity in the aortae during pregnancy of rats and ACh-induced relaxation is greatest on Day 21 in pregnancy, and that it may be due to the enhancement of NO synthesis in endothelium mainly by estradiol and partly by progesterone.

The effect of sodium based hypo-osmolality on arterial smooth muscle reactivity in vitro

The study tested the hypothesis that the reduced [Na+]e and hypo-osmolality of normal pregnancy are causally linked to the attenuation of vascular smooth muscle reactivity in vitro. Aortic rings from nonpregnant female rats were incubated in physiological medium containing 114 mM NaCl/l and the contractile responses to phenylephrine, KCl and CaCl2 as well as the relaxations to acetylcholine and KCl were compared with those of rings incubated in normal medium containing 119 mM NaCl/l. There was no solute substituted for the lowered [Na+]. Experiments with phenylephrine were repeated using de-endothelialized rings and intact rings pretreated with indomethacin. Contractile responses of intact rings (n = 11) in hypo-osmolar solution to phenylephrine were significantly (P < 0.001) lower than of those in normal medium (n = 11). Responses were partially restored by endothelial denudation but not in the presence of indomethacin. Relaxations to acetylcholine (n = 7 for hypo-osmolar; n = 6 for normal solution) and KCl (n = 7 for each of hypo- and normal osmolar) were significantly enhanced (P < 0.05) in rings incubated in hypo-osmolar solution. There was no significant difference between the responses of the rings to KCl, and CaCl2 in either solution. These effects are similar to some of those previously described for vascular smooth muscle in normal pregnancy suggesting that the reduced [Na+]e and hypo-osmolarity of normal pregnancy may be contributing to the diminished vascular reactivity.

A regional variation of acetylcholine-induced relaxation in different segments of rat aorta

The tension of the isolated thoracic aorta of the rat was measured isometrically to determine if there is a regional variation of the relaxation to acetylcholine (ACh). Endothelium-derived nitric oxide (NO)-dependent relaxation to ACh in the thoracic aorta precontracted with norepinephrine was significantly greater in the middle and distal segments than in the proximal segments. The relaxation to ACh was inhibited by NG-nitro-L-arginine methyl ester, an inhibitor of NO synthase. The relaxation to the NO donor sodium nitroprusside did not differ between the same three segments of the thoracic aorta. These results suggest that there are regional variations in the ACh-induced release of endothelium-derived NO in the rat thoracic aorta.

Comparison of endothelium-derived relaxing factor activity between nonpregnant and pregnant rats

The tension of isolated ring preparation of aorta from nonpregnant and pregnant rats was measured isometrically to study the effect of pregnancy on endothelium-derived relaxing factor activity. Contraction in response to norepinephrine and potassium chloride was greater in aortae from nonpregnant rats than in those from pregnant rats. The endothelium-dependent relaxation that was caused by acetylcholine (10(-10)-3 x 10(-9) M) in aortae precontracted with norepinephrine was significantly enhanced in aortae from pregnant rats compared with the relaxation in those from nonpregnant rats. NG-nitro-L-arginine methyl ester (L-NAME) inhibited the endothelium-dependent relaxation in both aorta from pregnant and nonpregnant rats. L-Arginine reversed the inhibition of L-NAME. Those results suggest that the enhanced endothelium-derived relaxing factor activity in rats aortae is associated with pregnancy.