Bleeding disorders: A common cause of menorrhagia in adolescents.

OBJECTIVE: To determine the frequency of underlying bleeding disorders in adolescents with menorrhagia. STUDY DESIGN: We retrospectively reviewed the charts of all girls, aged 10 to 19 years, who presented to our children's hospital for inpatient or outpatient evaluation of menorrhagia between January 1990 and November 1998. RESULTS: At presentation, 9 of the 71 girls (13%) had thrombocytopenia (platelet count <150,000/microL; range, 5000-106,000/microL). The most common causes for thrombocytopenia were immune thrombocytopenic purpura (n = 5) and myelosuppression caused by chemotherapy (n = 2). Of 14 girls who underwent a more detailed hemostatic evaluation, 8 were given a diagnosis of a hereditary coagulation disorder: 6 had platelet function defects and 2 had type 1 von Willebrand disease. Excessive menstrual bleeding commonly results in anemia. One half of the total group had anemia (hemoglobin <12.0 g/dL). Seven girls (10%) had potentially life-threatening anemia (hemoglobin <5.0 g/dL). CONCLUSIONS: Acquired and congenital bleeding disorders are common causes of menorrhagia in adolescent girls. Severe anemia is a frequent complication of menorrhagia. We recommend that adolescents without thrombocytopenia who present with menorrhagia receive a comprehensive hemostatic evaluation, including testing for von Willebrand disease and platelet function defects.

Dimensions and wall force development capacity of human pial arteries from normotensives is not altered in obesity.

OBJECTIVE: The dimensions and maximum wall tension capacity of segments of human pial arteries from normotensive obese and non-obese patients were compared. DESIGN: Segment size was assessed by quantitative morphometry of fixed sections and wall force by in vitro myography. SUBJECTS: Twenty normotensive non-obese and 13 normotensive obese humans body mass index (BMI) 22.4+/-0.5 and 33.9+/-1.7 kg/m(2), respectively) were studied. RESULTS: There was no significant difference in the perimeter of the outer medial border, the smoothed out length of the internal elastic lamina, the ratios of media thickness to area and lumen diameter and the maximum wall force development between the two groups. CONCLUSION: Obesity per se is not associated with initial dimensional changes nor capacity to develop wall tension that might lead to the emergence of hypertension.

Histamine-induced depolarization: ionic mechanisms and role in sustained contraction of rabbit cerebral arteries.

The role of membrane depolarization in the histamine-induced contraction of the rabbit middle cerebral artery was examined by simultaneous measurements of membrane potential and isometric force. Histamine (1-100 microM) induced a concentration-dependent sustained contraction associated with sustained depolarization. Action potentials were observed during depolarization caused by histamine but not by high-K(+) solution. K(+)-induced contraction was much smaller than sustained contraction associated with the same depolarization caused by histamine. Nifedipine attenuates histamine-induced sustained contraction by 80%, with no effect on depolarization. Inhibition of nonselective cation channels with Co(2+) (100-200 microM) reversed the histamine-induced depolarization and relaxed the arteries but induced only a minor change in K(+)-induced contraction. In the presence of Co(2+) and in low-Na(+) solution, histamine-evoked depolarization and contraction were transient. We conclude that nonselective cation channels contribute to histamine-induced sustained depolarization, which stimulates Ca(2+) influx through voltage-dependent Ca(2+) channels participating in contraction. The histamine-induced depolarization, although an important and necessary mechanism, cannot fully account for sustained contraction, which may be due in part to augmentation of currents through voltage-dependent Ca(2+) channels and Ca(2+) sensitization of the contractile process.

Role of intracellular Ca(2+) release in histamine-induced depolarization in rabbit middle cerebral artery.

The role of Ca(2+) mobilization from intracellular stores and Ca(2+)-activated Cl(-) channels in caffeine- and histamine-induced depolarization and contraction of the rabbit middle cerebral artery has been studied by recording membrane potential and isometric force. Caffeine induced a transient contraction and a transient followed by sustained depolarization. The transient depolarization was abolished by ryanodine, DIDS, and niflumic acid, suggesting involvement of Ca(2+)-activated Cl(-) channels. Histamine-evoked transient contraction in Ca(2+)-free solution was abolished by ryanodine or by caffeine-induced depletion of Ca(2+) stores. Ryanodine slowed the development of depolarization induced by histamine in Ca(2+)-containing solution but did not affect its magnitude. In arteries treated with 1 mM Co(2+), histamine elicited a transient depolarization and contraction, which was abolished by ryanodine. DIDS and niflumic acid reduced histamine-evoked depolarization and contraction. Histamine caused a sustained depolarization and contraction in low-Cl(-) solution. These results suggest that Ca(2+) mobilization from ryanodine-sensitive stores is involved in histamine-induced initial, but not sustained, depolarization and contraction. Ca(2+)-activated Cl(-) channels contribute mainly to histamine-induced initial depolarization and less importantly to sustained depolarization, which is most likely dependent on activation of nonselective cation channels.

Oxidized low-density lipoprotein enhances myogenic tone in the rabbit posterior cerebral artery through the release of endothelin-1.

BACKGROUND AND PURPOSE: Cerebral arteries develop stretch-induced myogenic tone, which plays an important role in the regulation of blood flow to the brain. Although the effect of oxidized LDL (Ox-LDL) on many aspects of the vascular endothelial and smooth muscle cell function have been extensively investigated, its influence on myogenic activity has not been studied. METHODS: The effect of Ox-LDL on the myogenic tone that develops in the perfused rabbit posterior cerebral artery at intramural pressures between 40 and 90 mm Hg was examined. RESULTS: Ox-LDL (10 microg/mL) significantly enhanced myogenic tone by 21.4+/-6.1% to 28.5+/-1.8% at 60 to 90 mm Hg pressure (P<0.05) but had no influence on norepinephrine- (0.5 to 1 micromol/L) and KCl (20 mmol/L)-induced constriction. Ox-LDL was effective whether the artery was exposed to it from the intraluminal or the extraluminal surface. Lysophosphatidylcholine (10 micromol/L), a lipid component of Ox-LDL, had an equivalent potentiating effect. Native LDL (100 microg/mL) was inactive. The myogenic tone-potentiating effect of Ox-LDL was abolished by endothelium removal but was not influenced by the NO synthase inhibitor N(G)-nitro-L-nitro-arginine methyl ester (50 micromol/L). This effect was reversed by the endothelin-1 (ET-1) antagonist BQ-123 (1 micromol/L). This concentration blocked 1 to 3 nmol/L ET-1-induced constriction without altering constriction induced by 40 mmol/L KCl. The potentiating effect was suppressed by the specific protein kinase C inhibitor chelerythrine (1 micromol/L). CONCLUSIONS: Ox-LDL enhances myogenic tone through the release of ET-1 from the endothelium of the rabbit posterior cerebral artery.

As human pial arteries (internal diameter 200-1000 microm) get smaller, their wall thickness and capacity to develop tension relative to their diameter increase.

Pial arteries play a key role in the regulation of human cerebral blood flow. However, many of the features and mechanisms that regulate the tone and diameters of these vessels cannot be studied in situ. One approach is to study in vitro segments of arteries obtained during neurosurgical procedures. The ratios of arterial media thickness to lumen diameter and of the capacity to develop wall force to lumen diameter have important functional consequences and are known to change in disease. Experiments were carried out on pial arteries from normotensive humans to determine the way in which these parameters vary with vessel size. Vessel dimensions--media thickness and lumen diameter were derived from fixed sections using quantitative morphometry. Wall force was measured using a resistance artery myograph. The ratio of media thickness to lumen diameter and of maximum tension developed to lumen diameter both increased as vessel diameter decreased. These ratios do not change over the age range of 15-75 years. These findings show that although in vivo intralumenal pressure falls as human pial arteries become smaller, their media thickness and capacity to develop tone increase.

Functional changes in human pial arteries (300 to 900 micrometer ID) within 48 hours of aneurysmal subarachnoid hemorrhage.

BACKGROUND AND PURPOSE: Animal studies of cerebral arteries 2 to 3 days after experimental subarachnoid hemorrhage (SAH) provide evidence of arterial change such as hyperresponsiveness to contractile agonists. There is evidence that small arteries, as well as those large enough to be seen on angiography, may be involved. To directly test these possibilities, the contractile and dilator responses of pial artery segments taken from patients up to 48 hours after SAH were compared with those from patients having elective surgery for an aneurysm (Clip) and with those from normal brain vessels overlying tumors (controls). METHODS: Segments were mounted on a resistance artery myograph for measurements of wall force changes. RESULTS: There were no differences in maximum contractility (Emax) of the 3 groups of segments. The responses of the SAH segments to K+ (30 mmol/L) were 60.7+/-4.6% of Emax (n [number of vessels]=18), which was significantly greater than those of controls (29.9+/-5% Emax) (n=20). Clip responses were the same as control. Contractions of SAH segments to norepinephrine (1 micromol/L) were 54.3+/-7.9% Emax (n=12), and these were significantly greater than those of controls (15.1+/-6.2% Emax) (n=25). All SAH segments showed spontaneous contractile activity of varying patterns. Spontaneous activity did not occur in the Clip group and occurred in only 50% of control segments. Dilation to acetylcholine was numerically less in SAH and Clip segments than in controls, but differences were not statistically significant. The change in agonist responsiveness could result from exposure to agents that damage the blood vessel wall, resulting in partial depolarization of endothelial and smooth muscle cells. CONCLUSIONS: Small human pial arteries are hyperresponsive to contractile agents and show spontaneous contractile activity within 48 hours of SAH. Such effects could result in narrowed resistance arteries and reduction in cerebral blood flow. These effects emphasize the wisdom of early therapeutic intervention.

Barium and 4-aminopyridine inhibit flow-initiated endothelium-independent relaxation.

Although much is known about the underlying mechanism of endothelium-dependent flow-induced vasorelaxation, the cellular processes responsible for the endothelium-independent flow-induced relaxation observed in some vessels is unknown. As there is evidence for the participation of K+ channels in the endothelium-dependent response, the present study was designed to determine whether such channels are involved in the endothelium-independent response and if so, which ones. We examined the effects of various selective K+ channel blockers on endothelium-independent relaxation initiated by intraluminal flow (10-80 microl/min), and by an endothelium-independent vasodilator sodium nitroprusside (SNP, 1 nmol/l to 3 micromol/l) in segments of the rabbit facial vein under isometric conditions. Flow-initiated relaxation was abolished by 25 and 40 mmol/l K+ as well as 10 mmol/l tetraethylammonium (TEA), significantly inhibited by 100 micromol/l Ba2+, 5 mmol/l Cs+ and 7.5 mmol/l 4-aminopyridine (4-AP), but unaffected by 5 micromol/l glibenclamide and 50 nmol/l charybdotoxin. Relaxation induced by SNP was reduced by 7.5 mmol/l 4-AP, but not by any of the above drugs in their listed concentrations. The inhibitory effect of 100 micromol/l Ba2+ on the relaxation caused by low concentrations of K+ (15-20 mmol/l) supports the presence of inward rectifier K+ channels in the vascular smooth muscle cells of this tissue. We speculate that endothelium-independent flow-initiated relaxation of the rabbit facial vein may be associated with activation of inward rectifier and voltage-dependent K+ channels. The latter may also contribute to the vasorelaxation initiated by SNP.

Responsiveness of human infant cerebral arteries to sympathetic nerve stimulation and vasoactive agents.

Responses of segments of basilar and middle cerebral arteries of eight human infants to activation of perivascular nerves and to vasoactive drugs were studied using a resistance artery myograph. The infants ages ranged from 23 wk of gestation to 34 postnatal days. Neurogenic vasoconstriction occurred in all segments and at 8 Hz was 12.7 +/- 3.5% (11%) of tissue maximum and was blocked by phentolamine (10(-6) M). There was no evidence of a neurogenic dilator response. Catecholamine histofluorescence was seen in nerves in the adventitia at all ages studied. Norepinephrine ED50 was 7.6 +/- 1.8 x 10(-7) M, and its maximum effect was 43.1 +/- 5.7% of tissue maximum. Both neural and norepinephrine responses were greater than those of the proximal parts of adult human middle cerebral arteries obtained postmortem and surgically removed adult human pial arteries. Electron microscopy demonstrated that neural density at the adventitiomedial junction in the infant vessels was greater than in the pial arteries. Constrictor responses to serotonin and prostaglandin F2 alpha were minimal in the two infants of 23 and 24 wk of gestation but were clearly present in the older infants. Histamine and acetylcholine were potent vasodilators. Indomethacin potentiated agonist-induced contraction. In a limited number of trials angiotensin II, neuropeptide Y, caused contraction and bradykinin, relaxation. It is concluded that there is a quantitative similarity between the studied responses of infant cerebral artery segments and human pial arteries of similar diameter. However, sympathetic nerves may potentially play a more important role in the regulation of cerebrovascular tone in the infant compared with the adult, and during the gestational period examined these vessels possess an indomethacin-sensitive system that buffers agonist tone.

Nitric oxide inhibits alpha2-adrenoceptor-mediated endothelium-dependent vasodilation.

This study was designed to investigate the interaction between the NO/L-arginine pathway and the alpha2-adrenoceptor-mediated endothelium-dependent vasorelaxation. Reactivity of isolated resistance mesenteric arterial segments from mice lacking the gene for constitutive endothelial NO synthase (eNOS- mice, n=14) and from their wild-type controls (WT mice, n=46) was studied in isometric conditions in the presence of indomethacin (blocker of cyclooxygenase). Oxymetazoline (OXY, 0.01 to 30 micromol/L; a selective alpha2-adrenoceptor agonist) induced an endothelium-dependent relaxation of eNOS- but not WT arteries preconstricted either with phenylephrine or serotonin. In the presence of Nomega-nitro-L-arginine (l-NNA, 100 micromol/L), an inhibitor of NOS, OXY induced an endothelium-dependent relaxation of WT mesenteric arteries. l-NNA had no effect on the relaxation caused by OXY in eNOS- arterial rings. Therefore, the relaxation caused by OXY was independent of NO formation. To demonstrate the inhibitory role of NO on the alpha2-adrenoceptor-mediated relaxation, subthreshold (0.1 nmol/L) to threshold (1 nmol/L) concentrations of sodium nitroprusside (donor of NO) were added to l-NNA-treated arteries before OXY challenges: in these conditions, the alpha2-adrenoceptor-mediated relaxation of eNOS- and WT arteries was inhibited. OXY-induced relaxation was restored on readdition of methylene blue (1 micromol/L, inhibitor of guanylate cyclase), suggesting that cGMP may be the mechanism of inhibition of the alpha2-adrenergic pathway in the presence of NO. Finally, OXY-mediated relaxation was blocked by tetraethylammonium (1 mmol/L) but not glibenclamide (1 micromol/L), suggesting the involvement of an endothelium-derived hyperpolarizing factor that activates Ca2+-activated K+ channels. In conclusion, alpha2-adrenoceptor activation caused relaxation of isolated murine mesenteric arteries that was functionally blocked by NO through a mechanism that may involve activation of the soluble guanylate cyclase and cGMP formation. The endothelium-dependent alpha2-adrenoceptor-mediated relaxation is likely to be due to an endothelium-derived hyperpolarizing factor, whose release and/or production is reduced by concurrent NO formation.

High levels of myogenic tone antagonize the dilator response to flow of small rabbit cerebral arteries.

BACKGROUND AND PURPOSE: Pressure and shear stress exerted by flowing blood are two mechanical forces that play a major role in the regulation of vascular tone. We sought to evaluate the interaction between pressure and flow in isolated rabbit cerebral arteries. METHODS: Responses to intraluminal flow of isolated pressurized rabbit posterior cerebral arteries were investigated at low, medium, and high levels of myogenic tone by setting the luminal pressure at 40, 60, and 80 mm Hg, respectively. RESULTS: At both low and medium levels of myogenic tone, flow induced dilation. The response was significantly larger at 40 than at 60 mm Hg. At the high level of myogenic tone, the response to flow consisted of a combination of an initial transient dilation followed by sustained constriction. Flow-induced dilation but not flow-induced constriction response was endothelium dependent. Removal of the endothelium inhibited the dilator response by approximately 80%. Flow-induced dilation was inhibited (approximately 40%) by N omega-nitro-L-arginine (100 mumol/L) but not by indomethacin (10 mumol/L). Endothelium removal not only decreased the amplitude of flow-induced dilation but also promoted the appearance of flow-induced constriction at low and medium levels of myogenic tone. CONCLUSIONS: The intraluminal pressure and in consequence the level of myogenic tone at which flow is applied determine the nature of the response of the smooth muscle cells of the blood vessel wall.

Intrinsic tone of cerebral artery segments of human infants between 23 weeks of gestation and term.

Segments of basilar and middle cerebral arteries of eight human preterm and early postnatal infants have been examined using the resistance artery myograph technique for wire-mounted segments and the pressure perfusion arteriograph. Myograph-mounted segments spontaneously developed tone of varying duration and time course. Perfused segments showed maintained tone levels of approximately 40% of maximum possible constriction when the intraluminal pressure was 60 mm Hg. This level is not different from that found in adult human pial arteries of similar lumen diameter. Indomethacin (10[-5] M) either initiated tone increase or potentiated existing tone in the isometrically mounted segments. After washout of vasoconstrictors norepinephrine (10[-6] M) and angiotensin II (10[-8] M), indomethacin caused a pronounced, long lasting increase in basal tone. Spontaneous tone was reversed by acetylcholine (10[-6] M), isoproterenol (10[-8] to 10[-5] M), histamine (10[-8] to 10[-5] M), and papaverine (10[-5] M). Low levels of tone were increased and higher levels decreased by intraluminal flow. The pressure/diameter curves of these vessels were of similar shape as those of the equivalent size in the adult. It is concluded that intrinsic tone is a prominent feature of these large cerebral arteries, and it is modified by an endogenous indomethacin-sensitive process.

Weakness of sympathetic neural control of human pial compared with superficial temporal arteries reflects low innervation density and poor sympathetic responsiveness.

BACKGROUND AND PURPOSE: The primary goal of these studies was to understand and investigate the capacity of perivascular nerves to influence the tone of human pial arteries and to compare them with other human cephalic arteries, the superficial temporal and middle meningeal. METHODS: Responses to electrical activation of intramural nerves and related features of fresh segments of human cephalic arteries-the pial (PA; 478+/-34 microm ID), middle meningeal (MMA; 540+/-41 microm ID), and superficial temporal (STA; 639+/-49 microm ID)-obtained from patients aged 15 to 82 years during surgical procedures were studied on a resistance artery myograph. RESULTS: The PA segment responses to electrical nerve activation and to norepinephrine (NE; 10[-5] mol/L) were 1% and 21% of tissue maximum, respectively, compared with 6% and 34% for the MMA and 14% and 90% for the STA. Tissue maximum was defined as the force increase to 127 mmol/L KCl plus arginine vasopressin (1 microm). All arteries dilated well to acetylcholine. Possible explanations for the PA marginal neurogenic responses were assessed. NE ED50 was 5.4+/-2.2 X 10(-7) mol/L and did not vary with age or diameter. NE responsiveness did not increase in vessels with spontaneous or raised potassium-induced tone. Relaxation to isoproterenol was variable and propranolol did not increase the neurogenic response. Neither N(G)-monomethyl-L-arginine, N(G)-nitro-L-arginine methyl ester, endothelium removal, nor indomethacin consistently influenced the contractions to NE or neurogenic reactivity. The weak PA neurogenic response is in keeping with its poor innervation. As determined by catecholamine histofluorescence, innervation in the PA is sparse, with density increasing in the order PA, MMA, and STA. The incidence of nerve structures in the PA adventitio-medial junction was only 3% of those in the STA, and these were situated more than 3 microm from the closest smooth muscle cell. CONCLUSIONS: We conclude that the weak neurogenic response of adult human pial artery reflects its poor innervation and responsiveness to NE, implying that these features are not important in the regulation of its diameter.

Diameter dependence of myogenic tone of human pial arteries. Possible relation to distensibility.

BACKGROUND AND PURPOSE: Responses to changes in intraluminal pressure of isolated human pial arteries (200 to 1200 microns i.d.) obtained from patients undergoing neurosurgery were measured. METHODS: The vessels were cannulated and pressurized (60 mm Hg); vascular diameter and intraluminal pressure were recorded simultaneously. After spontaneous development of steady state tone, intraluminal pressure was changed to both higher and lower levels in random sequence. RESULTS: Human pial arteries exhibited myogenic responses and maintained their diameter over the pressure range of 20 to 100 mm Hg. The level of myogenic tone observed at 30 mm Hg did not vary significantly with artery diameter. In contrast, at 60 and 90 mm Hg, the extent of myogenic tone increased as the diameter decreased (up to 70% to 80% of maximum in 200-microns i.d. arteries). The arteries contracted to KCl 30 mmol/L, norepinephrine 1 mumol/L, and vasopressin 0.1 mumol/L and relaxed to acetylcholine 3 mumol/L. The extent of these responses did not vary with the diameter of the artery. Arterial distensibility, represented by the slope of the tangent of the passive pressure-diameter curve at lower pressures (5 to 50 mm Hg), increased as arteries became smaller. This is consistent with the possibility that the level of myogenic tone is related to vessel distensibility. Human omental arteries of comparable size did not develop myogenic tone but contracted to KCl and norepinephrine and relaxed to acetylcholine to an extent similar to pial arteries. CONCLUSIONS: There is a specific gradient of myogenic responsiveness in human pial arteries that varies inversely with their diameter. This tone does not develop in all vascular beds. These levels of tone in the pial circulation would be expected to be of profound functional significance by allowing blood flow to vary widely.

Shear stress, the endothelium and the balance between flow-induced contraction and dilation in animals and man.

Dilation is the most commonly observed diameter change in blood vessels when intraluminal flow increases. However, at very high and low levels of vascular tone the response is constriction. This complex response seems designed to ensure that time-averaged vascular tone levels are restricted to an intermediate range. Flow dilation is initiated predominantly at the surface of the endothelium, probably by conformational change in macromolecules of the extracellular matrix such as glycosaminoglycans. This is associated with changes in ion binding--flow is exquisitely sodium sensitive, and subsequent alteration in cellular function. In the rabbit basilar artery the inward rectifying potassium channel of the endothelium cell is opened by shear stress increase leading to dilation and the voltage-dependent calcium channel of the smooth muscle cells with constriction. In this blood vessel, at any rate, the final response to flow change seems to be predominantly the consequence of the interaction between these two processes.

Reversal of endothelin-1 release by stimulation of endothelial alpha2-adrenoceptor contributes to cerebral vasorelaxation.

Agonists acting on the vascular endothelium can modulate the release of a number of factors that interact with the surrounding smooth muscle cells and influence their tone. One such factor is the vasoconstricting agent endothelin-1 (ET-1), which has been implicated in several disease states, including stroke. However, very little is known about the physiological role of ET-1 in the cerebral circulation. We demonstrate that activation of alpha2-adrenoceptors in human pial artery endothelial cells reduces both constitutive and agonist-stimulated release of immunoreactive ET-1. That this has physiological relevance is supported by our demonstration that in segments of rabbit middle cerebral arteries, alpha2-adrenoceptor activation reduces the release of endothelium-derived ET-1 and causes an endothelium-dependent relaxation. The adrenoceptor-dependent relaxation was not blocked by combined addition of indomethacin and N omega-nitro-L-arginine in 25 mmol/L KCl-depolarizing physiological solution but was selectively antagonized by a subthreshold concentration of exogenous ET-1. Our data suggest that activation of endothelial alpha2-adrenoceptor would favor a decrease in ET-1 production and possibly promote vascular relaxation.

Pulmonary vasoconstriction and hypertension in mice with targeted disruption of the endothelial nitric oxide synthase (NOS 3) gene.

NO, synthesized in endothelial cells by endothelial NO synthase (NOS 3), is believed to be an important endogenous pulmonary vasodilator substance that contributes to the normal low pulmonary vascular resistance. To selectively investigate the role of NOS 3 in the pulmonary circulation, mice with targeted disruption of the NOS 3 gene were studied. Pulmonary hemodynamics were studied by measuring pulmonary artery pressure, left ventricular end-diastolic pressure, and lower thoracic aortic flow by using a novel open-chest technique. Transient partial occlusion of the inferior vena cava was used to assess the pulmonary artery pressure-flow relationship. Tension developed by isolated pulmonary artery segments after acetylcholine stimulation was measured in vitro. The histological appearance of NOS 3-deficient and wild-type murine lungs was compared. NOS 3-deficient mice (n = 27), when compared with wild-type mice (n = 32), had pulmonary hypertension (pulmonary artery pressure, 19.0 +/- 0.8 versus 16.4 +/- 0.6 mm Hg [mean +/- SE]; P < .05) that was due to an increased total pulmonary resistance (62 +/- 6 versus 33 +/- 2 mm Hg.min.g.mL-1; P < .001). In vitro, acetylcholine induced vasodilation in the main pulmonary arteries of wild-type but not NOS 3-deficient mice. The morphology of the lungs of NOS 3-deficient mice did not differ from that of wild-type mice. We conclude that NOS 3 is a key enzyme responsible for providing basal pulmonary NO release. Congenital NOS 3 deficiency produces mild pulmonary hypertension in mice.

Human vascular endothelium heterogeneity. A comparative study of cerebral and peripheral cultured vascular endothelial cells.

BACKGROUND AND PURPOSE: Hormones, neurotransmitters, and autacoids play a key role in the regulation of vascular tone as a result of their interaction with the endothelium. The aim of this study was to compare selected properties of three human endothelial cell lines isolated from cerebral pial arteries (PEC) and two peripheral vessels, the superficial temporal (SEC) and omental (OEC) arteries. METHODS: Intracellular free calcium concentration ([Ca2+]i) and receptor protein expression were measured in characterized primary cultures of human endothelial cells. RESULTS: All cell lines labeled positively for factor VIII/von Willebrand factor. Growth rate and constitutive release of endothelin-1, expressed as a function of protein, were both significantly lower in cerebral cells (PEC) than in endothelial cells derived from peripheral vessels. Basal [Ca2+]i measured with the fluorescent calcium indicator fura 2-AM (2 mumol/L) did not differ in either of the three cell lines. Although PEC responded to endothelin-1 (0.1 mumol/L) and vasoactive intestinal peptide (1 mumol/L) by a twofold to threefold increase in [Ca2+]i, OEC were unresponsive to these peptides. Moreover, the calcium response to alpha-thrombin (10 nmol/L) was greater in cerebral (PEC) than in peripheral (SEC, OEC) endothelial cells, while bradykinin (100 nmol/L) increased [Ca2+]i to a similar level in all three cell types. CONCLUSIONS: This study demonstrates that endothelial cells from different sites of the vasculature exhibit different growth rates and vary in their response to agonists.

Small changes in extracellular sodium influence myogenic tone in rabbit facial vein by changing its sensitivity to calcium.

Extracellular Na+ concentration ([Na+]e) significantly effects the regulation of myogenic tone in isolated blood vessels. We examined the effect of small changes in [Na+]e on simultaneous changes in stretch-activated myogenic tone in rabbit facial vein and 45Ca2+ unidirectional influx and net uptake. Decreasing [Na+]e from 150 to 120 mmol/l augmented myogenic tone (control: 3.15 +/- 0.27 mN, n = 22) by 89 +/- 29%, while raising [Na+]e to 165 mmol/l attenuated myogenic tone to 80 +/- 2% of control. Changes in myogenic tone induced by alterations in [Na+]e were not accompanied by proportional changes in 45Ca2+ net uptake. 45Ca2+ unidirectional influx per unit of wall force (10.2 +/- 1.0 pmol/mg per mN force, n = 22, control) was decreased to 6.1 +/- 0.6 pmol/mg per mN (n = 20, P < 0.05) and increased to 21.0 +/- 2.5 pmol/mg per mN (n = 14, P < 0.05) when [Na+]e was 120 or 165 mmol/l, respectively, suggesting that decreasing [Na+]e is related to an increased sensitivity to calcium. We conclude that, in the rabbit facial vein, the sensitivity of myogenic tone to changes in [Na+]e may reflect changes in the sensitivity of smooth muscle to Ca2+ through a change in mechanoreceptor sensitivity.