Abstract-Evidence exists that NO plays a role in the vasodilation that occurs during pregnancy. The purpose of the present study was to determine whether the role of NO is associated with an increase in the activity and protein expression of NO synthase (NOS) in the human uterine artery. Uterine arteries were obtained from pregnant patients (P arteries) and nonpregnant patients (NP arteries). NOS activity was estimated with the L-[ 3 H]-arginine-to-L-[ 3 H]-citrulline conversion method and on the basis of changes in tissue levels of cGMP. Western immunoblotting and immunohistochemistry were used to assess NOS protein expression. Ca 2ϩ -dependent NOS activity was 8 times greater (PϽ0.01) in P than in NP arteries. Although most of this pregnancy-induced increase in NOS activity was Ca 2ϩ dependent (64%), a considerable portion was Ca 2ϩ independent. Expressions of endothelial NOS (eNOS) and neuronal NOS, but not inducible NOS, were demonstrated in P and NP arteries. The eNOS was located in the endothelium and stained with a qualitative order of P arteriesϾNP arteries (follicular)ϾNP arteries (luteal). The neuronal NOS was located in the adventitia of P and NP arteries. Basal NO-dependent and bradykinin-stimulated levels of cGMP were higher (PϽ0.05) in P than in NP arteries. These results indicate that an upregulation of eNOS protein expression could account for the increased NO synthesis/release in the human uterine artery during pregnancy. (Circ Res. 2000;87:406-411.)ormal pregnancy is associated with an increase in uterine blood flow and a decrease in uterine vascular resistance. [1][2][3][4] The low resistance is attributed to a loss of smooth muscle in myometrial resistance vessels (spiral arteries and terminations of radial arteries) as well as to dilation of the larger uterine arteries. 5 The dilation of the uterine arteries could be due to an increased role of endogenous vasodilators.Considerable evidence indicates that NO plays a role in pregnancy-induced uterine vasodilation. We have previously reported that acetylcholine is more potent and efficacious in producing dilation of isolated uterine arteries from pregnant than from nonpregnant patients. 6,7 The acetylcholine-induced relaxation was blocked by NO synthase (NOS) inhibitors and thus is apparently mediated by NO. 6,7 Furthermore, pregnancy-induced increases in basal NO production have been found in the uterine vasculature of rats, 8,9 guinea pigs, 10,11 and sheep. 3,12,13 NO is produced by NOS, of which 3 isoforms have been identified: endothelial NOS (eNOS), neuronal NOS (nNOS), and inducible NOS (iNOS). 14 The NOS isoforms share a common overall catalytic scheme for the oxidation of L-arginine to NO and L-citrulline but can be divided into 2 functional classes based on the dependence of Ca 2ϩ for activity. 14 The constitutive forms, eNOS and nNOS, require Ca 2ϩ for activity, but the inducible isoform, iNOS, has a Ca 2ϩ -independent activity. Ca 2ϩ -independent activity for eNOS also has been reported. [15][16][17][18] In the present study, we te...

The influence of pregnancy on the dilator effects of acetylcholine in the isolated human uterine artery was investigated. Acetylcholine (0.1 nM to 0.1 microM) produced concentration- and endothelium-dependent relaxation of norepinephrine (3 microM)-induced contraction. The relaxation was greater in arteries from pregnant patients (P arteries) than from non-pregnant patients (NP arteries). The maximal relaxation was 53.5+/-3.4% (n=21) in P arteries and 23.5+/-2.5% (n=35) in NP arteries. In both P and NP arteries the cholinergic relaxation was increased in the presence of superoxide dismutase and greatly reduced in the presence of the nitric oxide synthase inhibitors, NG-mono-methyl L-arginine (L-NMMA) and L-nitro-arginine-methylester (L-NAME). The effect of these nitric oxide synthase inhibitors was reversed by L-arginine. We conclude that pregnancy enhances acetylcholine-induced nitric oxide synthesis and release in the human uterine artery.

The responses to electrical field stimulation (EFS) of perivascular nerves in human uterine arteries were characterized. The arteries were removed from pregnant and nonpregnant patients undergoing hysterectomy. Tetrodotoxin, guanethidine, and phentolamine blocked EFS (2 min, 80 V, 0.1-ms duration)-induced constriction. The constrictions and the endogenous norepinephrine levels were lower (P < 0.01) in uterine arteries from pregnant than from nonpregnant patients. When arterial rings were precontracted, the response to EFS was biphasic, consisting of an initial constriction followed by a postconstriction relaxation. The EFS-induced relaxation was endothelium independent and was greater (P < 0.01) in uterine arteries from pregnant than from nonpregnant patients. The relaxation was enhanced by guanethidine and superoxide dismutase, inhibited by nitric oxide synthase inhibitors, blocked by tetrodotoxin, and unaffected by atropine, propranolol, or indomethacin. The results demonstrate that human uterine arteries respond to EFS with contraction and relaxation and that these responses may be mediated, respectively, by norepinephrine and, in part, by nitric oxide released from periarterial nerves. The decrease in neuronally mediated uterine arterial constriction and the increase in dilation could be physiological mechanisms for ensuring appropriate uteroplacental perfusion.

The present study examined reactivity to norepinephrine (NE) and KCl in isolated, suffused blood vessels from the systemic and pulmonary circulations of endotoxin-treated and control sheep. A possible mechanism underlying an endotoxin-induced alteration in vascular reactivity was also investigated. Chronically instrumented sheep were given Escherichia coli endotoxin (1.5 micrograms/kg). Eight to 12 h later these endotoxin-treated animals exhibited a significantly increased cardiac output and decreased systemic vascular pressure and resistance. The pulmonary vascular pressure and resistance were not changed. The isolated superficial femoral artery from the endotoxin sheep exhibited depressed contractions in response to KCl (75 mM) and to NE (10(-7)-10(-5) M), whereas the pulmonary artery (tertiary branch) did not exhibit altered reactivity. The decreased sensitivity to NE in the femoral artery from endotoxin sheep did not appear to involve an alteration of alpha- or beta-adrenoceptors, or an increased release of vasodilator prostanoids, or endothelium-derived relaxing factor.

Blood pressure and heart rate often increase during cocaine intoxication, but the mechanisms of these cardiovascular responses are poorly understood. The most often suggested theories are central nervous system mechanisms involving the blockade of neuronal transmitter uptake. Cocaine also has potent local anesthetic properties, and in this study we tested the possible role of peripheral actions of cocaine at baroreceptor afferents. Single fiber baroreceptors were recorded using an in vitro preparation of the rat aortic arch. Diameter, pressure, and baroreceptor discharge were recorded. Cocaine perfused through the lumen of the aortic arch at a suprathreshold pressure reduced baroreceptor discharge within 90 s of entering the lumen of the aorta. Slow ramps of pressure elicited complete pressure- and diameter-discharge curves every 5 min. Beginning at about 1 microM, cocaine inhibited baroreceptor function; threshold increased, the maximum discharge decreased, and at 100 microM cocaine, all discharge ceased. The vasodilator nitroprusside or the alpha 1-adrenoreceptor antagonist prazosin did not affect baroreceptor responses to cocaine. In in vivo tests in rabbits, cocaine that perfused through a vascularly isolated carotid sinus reduced the slope of the baroreflex relationship between carotid sinus pressure and systemic mean arterial pressure. Significant depression of baroreceptor function was found at concentrations similar to the plasma cocaine levels measured in clinical studies. The local anesthetic properties of cocaine may be involved in baroreceptor effects. Our studies suggest a possible contributing role of a new site of action of cocaine outside the central nervous system. Compromise of baroreceptor reflexes could facilitate the development of serious cardiovascular complications associated with cocaine abuse.