Nitric Oxide and Prostaglandins Modulate Pressure-Induced Myogenic Responses of Intramural Coronary Arterioles

Role of CB1 Cannabinoid Receptors in Vascular Responses and Vascular Remodeling of the Aorta in Female Mice

Both the endocannabinoid system (ECS) and estrogens have significant roles in cardiovascular control processes. Cannabinoid type 1 receptors (CB1Rs) mediate acute vasodilator and hypotensive effects, although their role in cardiovascular pathological conditions is still controversial. Estrogens exert cardiovascular protection in females. We aimed to study the impact of ECS on vascular functions. Experiments were performed on CB1R knockout (CB1R KO) and wild-type (WT) female mice. Plasma estrogen metabolite levels were determined. Abdominal aortas were isolated for myography and histology. Vascular effects of phenylephrine (Phe), angiotensin II, acetylcholine (Ach) and estradiol (E2) were obtained and repeated with inhibitors of nitric oxide synthase (NOS, Nω-nitro-L-arginine) and of cyclooxygenase (COX, indomethacin). Histological stainings (hematoxylin-eosin, resorcin-fuchsin) and immunostainings for endothelial NOS (eNOS), COX-2, estrogen receptors (ER-α, ER-β) were performed. Conjugated E2 levels were higher in CB1R KO compared to WT mice. Vasorelaxation responses to Ach and E2 were increased in CB1R KO mice, attenuated by NOS-inhibition. COX-inhibition decreased Phe-contractions, while it increased Ach-relaxation in the WT group but not in the CB1R KO. Effects of indomethacin on E2-relaxation in CB1R KO became opposite to that observed in WT. Histology revealed lower intima/media thickness and COX-2 density, higher eNOS and lower ER-β density in CB1R KO than in WT mice. CB1R KO female mice are characterized by increased vasorelaxation associated with increased utilization of endothelial NO and a decreased impact of constrictor prostanoids. Our results indicate that the absence or inhibition of CB1Rs may have beneficial vascular effects.

Tracking endothelium-dependent NO release in pressurized arteries

Background: Endothelial cell (EC) dysfunction is an early hallmark of cardiovascular disease associated with the reduced bioavailability of nitric oxide (NO) resulting in over-constriction of arteries. Despite the clear need to assess NO availability, current techniques do not reliably allow this in intact arteries. Methods: Confocal fluorescence microscopy was used to compare two NO-sensitive fluorescent dyes (NO-dyes), Cu2FL2E and DAR-4M AM, in both cell-free chambers and isolated, intact arteries. Intact rat mesenteric arteries were studied using pressure myography or en face imaging to visualize vascular smooth muscle cells (SMCs) and endothelial cells (ECs) under physiological conditions. Both NO-dyes irreversibly bind NO, so the time course of accumulated fluorescence during basal, EC-agonist (ACh, 1 µM), and NO donor (SNAP, 10 µM) responses were assessed and compared in all experimental conditions. To avoid motion artefact, we introduced the additional step of labelling the arterial elastin with AF-633 hydrazide (AF) and calculated the fluorescence ratio (FR) of NO-dye/elastin over time to provide data as FR/FR0. Results: In cell-free chambers using either Cu2FL2E or DAR-4M AM, the addition of SNAP caused a time-dependent and significant increase in fluorescence compared to baseline. Next, using pressure myography we demonstrate that both Cu2FL2E and DAR-4M AM could be loaded into arterial cells, but found each also labelled the elastin. However, despite the use of different approaches and the clear observation of NO-dye in SMCs or ECs, we were unable to measure increases in fluorescence in response to either ACh or SNAP when cells were loaded with Cu2FL2E. We then turned our attention to DAR-4M AM and observed increases in FR/FR0 following stimulation with either ACh or SNAP. The addition of each agent evoked an accumulating, time-dependent, and statistically significant increase in fluorescence within 30 min compared to time controls. These experiments were repeated in the presence of L-NAME, an NO synthase inhibitor, which blocked the increase in fluorescence on addition of ACh but not to SNAP. Conclusion: These data advance our understanding of vascular function and in the future will potentially allow us to establish whether ECs continuously release NO, even under basal conditions.

Dietary nitrate reduces blood pressure and cerebral artery velocity fluctuations and improves cerebral autoregulation in transient ischemic attack patients

We found dietary nitrate supplementation reduced blood pressure and brain blood flow fluctuations and improved the relationship between blood pressure and brain blood flow in transient ischemic attack patients. Meanwhile, dietary nitrate had no effects on the brain blood vessels’ response to CO2. We attribute the improved brain blood flow stability to the improved myogenic control of blood pressure with dietary nitrate. Our findings indicate that dietary nitrate could be an effective strategy for stabilizing blood pressure and brain blood flow following transient ischemic attack.

Remodeling of Wall Mechanics and the Myogenic Mechanism of Rat Intramural Coronary Arterioles in Response to a Short-Term Daily Exercise Program: Role of Endothelial Factors

PURPOSE

Exercise elicits early adaptation of coronary vessels enabling the coronary circulation to respond adequately to higher flow demands. We hypothesized that short-term daily exercise induces biomechanical and functional remodeling of the coronary resistance arteries related to pressure.

METHODS

Male rats were subjected to a progressively increasing 4-week treadmill exercise program (over 60 min/day, 1 mph in the final step). In vitro pressure-diameter measurements were performed on coronary segments (119 ± 5 μm in diameter at 50 mm Hg) with microarteriography. The magnitude of the myogenic response and contribution of endogenous nitric oxide and prostanoid production to the wall mechanics and pressure-diameter relationship were assessed.

RESULTS

Arterioles isolated from exercised ani mals - compared to the sedentary group - had thicker walls, increased distensibility, and a decreased elastic modulus as a result of reduced wall stress in the low pressure range. The arterioles of exercised rats exhibited a more powerful myogenic response and less endogenous vasoconstrictor prostanoid modulation at higher pressures, while vasodilator nitric oxide modulation of diameter was augmented at low pressures (< 60 mm Hg).

CONCLUSIONS

A short-term daily exercise program induces remodeling of rat intramural coronary arterioles, likely resulting in a greater range of coronary autoregulatory function (constrictor and dilator reserves) and more effective protection against great changes in intraluminal pressure, contributing thereby to the optimization of coronary blood flow during exercise.

Control of myogenic tone and agonist induced contraction of intramural coronary resistance arterioles by cannabinoid type 1 receptors and endocannabinoids

It was tested whether intrinsic CB₁R activation modifies myogenic and agonist induced contraction of intramural coronary resistance arteries of the rat. CB₁R protein was detected by immuno-histochemistry and by Western blot, its mRNA by qRT-PCR in their wall. Microsurgically prepared cylindrical coronary segments (∼100-150μm) developed myogenic contraction (∼20% of relaxed luminal diameter), from which a substantial relaxation (∼15%) in response to WIN55212 (a specific agonist of the CB₁Rs) has been found. CB₁R-mediated relaxation was blocked by O2050 and AM251 (neutral antagonist and inverse agonist of the CB₁R, respectively) and was partially blocked by the NO synthase blocker Nω-nitro-L-arginine. CB₁R blockade enhanced myogenic tone and augmented AngII-induced vasoconstriction (from 17.8±1.2 to 29.1±2.9%, p<0.05). Inhibition of diacylglycerol lipase by tetrahydrolipstatin, (inhibitor of endogenous 2-AG production) also augmented coronary vasoconstriction. These observations prove that vascular endocannabinoids are significant negative modulators of the myogenic and agonist-induced tone of intramural coronary arterioles acting through CB₁Rs.

Quantitative analysis of vasodilatory action of quercetin on intramural coronary resistance arteries of the rat in vitro

Background

Dietary quercetin improves cardiovascular health, relaxes some vascular smooth muscle and has been demonstrated to serve as a substrate for the cyclooxygenase enzyme.

Aims

1. To test quantitatively a potential direct vasodilatory effect on intramural coronary resistance artery segments, in different concentrations. 2. To scale vasorelaxation at different intraluminal pressure loads on such vessels of different size. 3. To test the potential role of prostanoids in vasodilatation induced by quercetin.

Methods

Coronary arterioles (70–240 µm) were prepared from 24 rats and pressurized in PSS, using a pressure microangiometer.

Results

The spontaneous tone that developed at 50 mmHg was relaxed by quercetin in the 10⁻⁹ moles/lit concentration (p<0.05), while 10⁻⁵ moles/lit caused full relaxation. Significant relaxation was observed at all pressure levels (10–100 mmHg) at 10⁻⁷ moles/lit concentration of quercetin. The cyclooxygenase blocker indomethacin (10⁻⁵moles/lit) induced no relaxation but contraction when physiological concentrations of quercetin were present in the tissue bath (p<0.02 with Anova), this contraction being more prominent in smaller vessels and in the higher pressure range (p<0.05, Pearson correlation). A further 2–8% contraction could be elicited by the NO blocker L-NAME (10⁻⁴ moles/lit).

Conclusion

These results demonstrate that circulating levels of quercetin (10⁻⁷ moles/lit) exhibit a substantial coronary vasodilatory effect. The extent of it is commeasurable with that of several other physiological mechanisms of coronary blood flow control. At least part of this relaxation is the result of an altered balance toward the production of endogenous vasodilatory prostanoids in the coronary arteriole wall.

Sex differences in the biomechanics and contractility of intramural coronary arteries in angiotensin II-induced hypertension

BACKGROUND

It is well known that sex differences occur in both the pathogenesis and therapy of hypertension. A deeper understanding of the underlying processes may be helpful when planning a personalized therapeutic strategy.

OBJECTIVE

In laboratory animal experiments, we studied the early mechanisms of vascular adaptation of the intramural small coronary arteries that play a fundamental role in the blood supply of the heart.

METHODS

In our study, an osmotic minipump was implanted into 10 male and 10 female Sprague-Dawley rats. The pump remained in situ for 4 weeks, infusing a dose of 100 ng/kg/min angiotensin II acetate. Four weeks later, the animals were killed, and the intramural coronary arteries from the left coronary branch, which are fundamentally responsible for the blood supply of the heart, were prepared. The pharmacologic reactivity and biomechanical properties of the prepared segments were studied in a tissue bath.

RESULTS

The relative heart mass and vessel wall thickness were greater in females than males (0.387 [0.009] g/100 g vs 0.306 [0.006] g/100 g body weight; 41.9 [4.09] μm vs 33.45 [3.37] μm on 50 mm Hg). The vessel tone and vasoconstriction in response to thromboxane agonists were, however, significantly more pronounced in males. The extent of relaxation in response to bradykinin was also greater in females. Although we observed inward eutrophic remodeling in females, an increase in wall stress and elastic modulus dominated in males.

CONCLUSION

The early steps of angiotensin II-dependent hypertension evoked very different adaptation mechanisms in males and females.

Angiotensin II induces vascular endocannabinoid release, which attenuates its vasoconstrictor effect via CB1 cannabinoid receptors

In the vascular system angiotensin II (Ang II) causes vasoconstriction via the activation of type 1 angiotensin receptors. Earlier reports have shown that in cellular expression systems diacylglycerol produced during type 1 angiotensin receptor signaling can be converted to 2-arachidonoylglycerol, an important endocannabinoid. Because activation of CB(1) cannabinoid receptors (CB(1)R) induces vasodilation and reduces blood pressure, we have tested the hypothesis that Ang II-induced 2-arachidonoylglycerol release can modulate its vasoconstrictor action in vascular tissue. Rat and mouse skeletal muscle arterioles and mouse saphenous arteries were isolated, pressurized, and subjected to microangiometry. Vascular expression of CB(1)R was demonstrated using Western blot and RT-PCR. In accordance with the functional relevance of these receptors WIN55212, a CB(1)R agonist, caused vasodilation, which was absent in CB(1)R knock-out mice. Inhibition of CB(1)Rs using O2050, a neutral antagonist, enhanced the vasoconstrictor effect of Ang II in wild type but not in CB(1)R knock-out mice. Inverse agonists of CB(1)R (SR141716 and AM251) and inhibition of diacylglycerol lipase using tetrahydrolipstatin also augmented the Ang II-induced vasoconstriction, suggesting that endocannabinoid release modulates this process via CB(1)R activation. This effect was independent of nitric-oxide synthase activity and endothelial function. These data demonstrate that Ang II stimulates vascular endocannabinoid formation, which attenuates its vasoconstrictor effect, suggesting that endocannabinoid release from the vascular wall and CB(1)R activation reduces the vasoconstrictor and hypertensive effects of Ang II.

Emerging role of G protein-coupled receptors in microvascular myogenic tone

Blood flow autoregulation results from the ability of resistance arteries to reduce or increase their diameters in response to changes in intravascular pressure. The mechanism by which arteries maintain a constant blood flow to organs over a range of pressures relies on this myogenic response, which defines the intrinsic property of the smooth muscle to contract in response to stretch. The resistance to flow created by myogenic tone (MT) prevents tissue damage and allows the maintenance of a constant perfusion, despite fluctuations in arterial pressure. Interventions targeting MT may provide a more rational therapeutic approach in vascular disorders, such as hypertension, vasospasm, chronic heart failure, or diabetes. Despite its early description by Bayliss in 1902, the cellular and molecular mechanisms underlying MT remain poorly understood. We now appreciate that MT requires a complex mechanotransduction converting a physical stimulus (pressure) into a biological response (change in vessel diameter). Although smooth muscle cell depolarization and a rise in intracellular calcium concentration are recognized as cornerstones of the myogenic response, the role of wall strain-induced formation of vasoactive mediators is less well established. The vascular system expresses a large variety of Class 1 G protein-coupled receptors (GPCR) activated by an eclectic range of chemical entities, including peptides, lipids, nucleotides, and amines. These messengers can function in blood vessels as vasoconstrictors. This review focuses on locally generated GPCR agonists and their proposed contributions to MT. Their interplay with pivotal G(q-11) and G(12-13) protein signalling is also discussed.

Angiotensin II-aldosterone interaction in human coronary microarteries involves GPR30, EGFR, and endothelial NO synthase

AIMS

The aim of this study was to investigate the aldosterone-angiotensin (Ang) II interaction in human coronary microarteries (HCMAs).

METHODS AND RESULTS

HCMAs, obtained from 75 heart-beating organ donors, were mounted in myographs and exposed to Ang II, either directly or following a 30-min pre-incubation with aldosterone, 17β-oestradiol, hydrocortisone, the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580, the extracellular regulated kinase 1/2 (ERK1/2) inhibitor PD98059, the GPR30 antagonist G15, or the epidermal growth factor receptor (EGFR) antagonist AG1478. Ang II constricted HCMAs in a concentration-dependent manner. All steroids, at nanomolar levels, potentiated Ang II and G15 prevented this effect. The potentiation disappeared or was reversed into Ang II antagonism at micromolar steroid levels. NO synthase (NOS) inhibition prevented the latter antagonism in the case of 17β-oestradiol, whereas both aldosterone and 17β-oestradiol at micro- (but not nano-) molar levels induced endothelial NOS phosphorylation in human umbilical vein endothelial cells. AG1478, but not SB203580 or PD98059, abolished the Ang II-induced contraction in the presence of aldosterone or 17β-oestradiol, and none of these drugs affected Ang II alone.

CONCLUSION

Steroids including aldosterone affect Ang II-induced vasoconstriction in a biphasic manner. Potentiation occurs at nanomolar steroid levels and depends on GPR30 and EGFR transactivation. At micromolar steroid levels, this potentiation either disappears (aldosterone and hydrocortisone) or is reversed into an inhibition (17β-oestradiol), and this is due to the endothelial NOS activation that occurs at such concentrations.

Characteristics of myogenic reactivity in isolated rat mesenteric veins

Mechanisms of mechanically induced venous tone and its interaction with the endothelium and key vasoactive neurohormones are not well established. We investigated the contribution of the endothelium, l-type voltage-operated calcium channels (l-VOCCs), and PKC and Rho kinase to myogenic reactivity in mesenteric vessels exposed to increasing transmural pressure. The interaction of myogenic reactivity with norepinephrine (NE) and endothelin-1 (ET-1) was also investigated. Pressure myography was used to study isolated, cannulated, third-order rat mesenteric small veins and arteries. NE and ET-1 concentration response curves were constructed at low, intermediate, and high transmural pressures. Myogenic reactivity was not altered by nitric oxide synthase inhibition with Nω-nitro-l-arginine (l-NNA; 100 μM) or endothelium removal in both vessels. l-VOCCs blockade (nifedipine, 1 μM) completely abolished arterial tone, while only partially reducing venous tone. PKC (chelerythrine, 2.5 μM) and Rho kinase (Y27632, 3 μM) inhibitors largely abolished venous and arterial myogenic reactivity. There was no significant difference in the sensitivity of NE or ET-1-induced contractions within vessels. However, veins were more sensitive to NE and ET-1 when compared with corresponding arteries at low, intermediate, and high transmural pressures, respectively. These results suggest that 1) myogenic factors are important contributors to net venous tone in mesenteric veins; 2) PKC and Rho activation are important in myogenic reactivity in both vessels, while l-VOCCs play a limited role in the veins vs. the arteries, and the endothelium does not appear to modulate myogenic reactivity in either vessel type; and 3) mesenteric veins maintain an enhanced sensitivity to NE and ET-1 compared with the arteries when studied under conditions of changing transmural distending pressure.

Endothelium-independent constriction of isolated, pressurized arterioles by Nomega-nitro-L-arginine methyl ester (L-NAME)

BACKGROUND AND PURPOSE

Nitric oxide synthase (NOS) inhibitors cause vasoconstriction in pressurized arterioles with myogenic tone. This suggests either tonic production of NO modulates myogenic tone or a direct, NOS-independent effect of the NOS inhibitors. The nature of the contractile effect of the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM) on pressurised arterioles was investigated.

EXPERIMENTAL APPROACH

Segments of rat cremaster muscle first-order arteriole were cannulated on glass micropipettes and maintained at an intraluminal pressure of 50, 70 or 120 mmHg.

KEY RESULTS

L-NAME and the related compound L-NA (100 microM) constricted pressurized vessels with myogenic tone. Removal of the endothelium did not cause constriction or alter myogenic tone, however the constrictor effect of L-NAME persisted. The constrictor effect of L-NAME was abolished by L-arginine (1 mM). Other NO and cGMP pathway inhibitors, including the nNOS inhibitor 7-nitroindazole (100 muM), the NO scavenger carboxy-PTIO (100 microM), the guanylate cyclase inhibitor ODQ (10 microM) and the cGMP inhibitor Rp-8CPT-cGMPS (10 microM) did not cause constriction of the arterioles. L-NAME caused a small (3-4 mV) but not statistically significant depolarization of the arteriolar smooth muscle at both pressures. The constrictor effect was not prevented by the K(+)-channel antagonist tetraethyl ammonium (TEA, 1 mM) or the K(ATP) channel antagonist glibenclamide (1 microM).

CONCLUSIONS AND IMPLICATIONS

These observations demonstrate that L-NAME causes an endothelium- and NOS-independent contraction of vascular smooth muscle in isolated skeletal muscle arterioles. It is suggested that the underlying mechanism relates to an arginine binding interaction.

Nitric oxide modulates the interaction of pressure-induced wall mechanics and myogenic response of rat intramural coronary arterioles

Interactions between the biomechanical characteristics and pressure-induced active response of coronary microvessels are still not well known. We tested the hypothesis that pressure-dependent biomechanical characteristics of the coronary vascular wall are modulated by the active myogenic response and local vasodilators. We have utilized data obtained previously in isolated rat intramural coronary arterioles (approximately 100 microm in diameter), in which the diameter was investigated as a function of intraluminal pressure (Szekeres et al.: J. Cardiovasc. Pharmacol., 43, 242-249, 2004). To characterize the magnitude of myogenic response, diameter was expressed as percent of passive diameter as a function of pressure (normalized diameter; ND). In addition, circumferential wall stress (WS) and incremental distensibility (ID) were calculated. In control conditions, after an initial increase between 0-30 mm Hg, ND decreased substantially as pressure increased from 30 to 150 mm Hg. Correspondingly, WS gradually increased as a function of pressure (from 0.3 +/- 0.03 to 34.7 +/- 4.4 kPa) exhibiting a plateau phase between 40-80 mm Hg. In contrast, ID decreased and reached negative values (min: -104.9 +/- 21.9 10(-6) m2/N at 50 mm Hg). Inhibition of nitric oxide (NO) synthase by L-NNA decreased basal diameter (approximately 35% at 2 mm Hg), eliminated pressure-induced changes in ND, reduced the slope of pressure-WS curve, and decreased ID at lower pressures. Simultaneous administration of L-NNA and adenosine (which restored initial diameter, i.e. length of smooth muscle) restored--in part--the pressure-induced reduction in ND, reversed the pressure-induced behavior of WS to control, but not that of ID. These results not only confirm that in coronary arterioles wall stress is regulated by the myogenic response, but also suggest that there is interplay between the mechanical behavior of the wall and the myogenic response. Furthermore, the presence of NO seems to be necessary for maintaining a higher distensibility of intramural coronary arterioles allowing increases in diameter to lower pressures, which then activate the myogenic mechanism resulting in constrictions and full development of myogenic tone, as indicated by the presence of negative slope of pressure-diameter curve in the presence of NO.

Effects of an oral glucose tolerance test on the myogenic response in healthy individuals

The myogenic response, the inherent ability of blood vessels to rapidly respond to changes in transmural pressure, is involved in local blood flow autoregulation. Animal studies suggest that both acute hyperglycemia and hyperinsulinemia may impair myogenic vasoconstriction. The purpose of this study was to examine the effects of an oral glucose load on brachial mean blood velocity (MBV) during increases in forearm transmural pressure in humans. Eight healthy men and women (38 +/- 5 yr) underwent an oral glucose tolerance test (OGTT). MBV (in cm/s; Doppler ultrasound) responses to a rise in forearm transmural pressure (arm tank suction, -50 mmHg) were studied before and every 30 min for 120 min during the OGTT. Before the start of the OGTT, MBV was lower than baseline values 30 and 60 s after the application of negative pressure. This suggests that myogenic constriction was present. During the OGTT, blood glucose rose from 88 +/- 2 to 120 +/- 6 mg/dl (P < 0.05) and insulin rose from 14 +/- 1 to 101 +/- 32 microU/ml (P < 0.05). Glucose loading attenuated the reduction in MBV with arm suction (Delta-0.73 +/- 0.14 vs. Delta-1.67 +/- 0.43 cm/s and Delta-1.07 +/- 0.14 vs. Delta-2.38 +/- 0.54 cm/s, respectively, during 30 and 60 s of suction postglucose compared with preglucose values; all P < 0.05). We observed no such time effect for myogenic responses during a sham OGTT. In an additional 5 subjects, glucose loading had no effect on brachial diameters with the application of negative pressure. Oral glucose loading leads to attenuated myogenic vasoconstriction in healthy individuals. The role that this diminished postglucose reactivity plays in mediating postprandial hypotension and/or orthostasis needs to be further explored.

Extravascular pressure modulates responses of isolated rat coronary arteries to vasodilator, but not vasoconstrictor, stimuli

The aims of the study were to investigate whether elevated extravascular pressure modulates responses of isolated rat coronary arteries to constrictor and dilator stimuli. Isolated segments of rat coronary artery were mounted in a modified pressure myograph system that allowed independent modulation of both intra- and extravascular pressures. The influence of elevated extravascular pressure on stable levels of myogenic tone and on responses to vasoconstrictor and vasodilator stimuli was investigated at constant overall transmural pressures. Stable levels of myogenic tone were independent of the relative levels of intra- and extravascular pressure, as were responses to depolarization and to addition of the thromboxane agonist U-46619. Elevating extravascular pressure, however, significantly reduced dilatory responses to introduction of intraluminal flow and to addition of endothelium-dependent and endothelium-independent vasodilatory agonists. These results support the notion that elevated extravascular pressure may attenuate responses of coronary arteries to a variety of dilatory stimuli. This finding may be of relevance to cardiac disorders associated with elevated ventricular pressures.

Increased myogenic tone in 7-month-old adult male but not female offspring from rat dams exposed to hypoxia during pregnancy

Intrauterine growth restriction (IUGR) increases the risk of cardiovascular disease later in life. Vascular dysfunction occurs in adult offspring from animal models of IUGR including maternal undernutrition, but the influence of reduced fetal oxygen supply on adult vascular function is unclear. Myogenic responses, essential for vascular tone regulation, have not been evaluated in these offspring. We hypothesized that 7-mo-old offspring from hypoxic (12% O(2); H) or nutrient-restricted (40% of control; NR) rat dams would show greater myogenic responses than their 4-mo-old littermates or control (C) offspring through impaired modulation by vasodilators. Growth restriction occurred in male H (P < 0.01), male NR (P < 0.01), and female NR (P < 0.02), but not female H, offspring. Myogenic responses in mesenteric arteries from males but not females were increased at 7 mo in H (P < 0.01) and NR (P < 0.05) vs. C offspring. There was less modulation of myogenic responses after inhibition of nitric oxide synthase (P < 0.05), prostaglandin H synthase (P < 0.005), or both enzymes (P < 0.001) in arteries from 7-mo male H vs. C offspring. Thus reduced vasodilator modulation may explain elevated myogenic responses in 7-mo male H offspring. In contrast, there was increased modulation of myogenic responses in arteries from 7-mo female H vs. C or NR offspring after inhibition of both enzymes (P < 0.05). Thus increased vasodilator modulation may maintain myogenic responses in female H offspring at control levels. In summary, vascular responses in adult offspring from adverse intrauterine environments are impaired in a gender-specific, age-dependent, and maternal insult-dependent manner, with males more profoundly affected.

Mechanism of Contraction of Rat Isolated Tail Arteries by Hyposmotic Solutions

Contraction induced by hyposmotic swelling was examined in rat tail arteries mounted on a myograph containing a modified Krebs physiological saline solution (PSS) containing 50 mM mannitol (300 mosm/l). Hyposmotic swelling was induced by removing mannitol. In arteries having basal tone or arteries precontracted with K(+) or the thromboxane mimetic U-46619, removal of mannitol caused a concentration dependent contraction of rat tail arteries. Concurrent measurement of tension and intracellular calcium [Ca(2+)](i )in arteries loaded with fura-2 showed that both tension and [Ca(2+)](i) increased on exposure to a hyposmotic solution. Removal of endothelium or inhibition of nitric oxide and cyclooxygenase together did not affect contractile responses. Removal of extracellular Ca(2+) abolished the contractile response to hyposmotic solution and NiCl(2), a nonspecific inhibitor of Ca(2+) influx pathways, blocked the rise in [Ca(2+)](i) and tension in response to a hyposmotic solution. Verapamil and nisoldipine, inhibitors of Ca(v)1.2 (L-type) calcium channels significantly reduced the contractile response to a hyposmotic solution. Addition of NiCl(2) to nisoldipine caused an additional inhibition of the response to a hyposmotic solution. Inhibition of calcium release from the sarcoplasmic reticulum by ryanodine or cyclopiazonic acid (CPA) did not cause any change in the tension response to a hyposmotic solution. CPA did not significantly inhibit the response to a hyposmotic solution in the presence of N(G)-methyl-L-arginine, oxyhaemoglobin and indomethacin. We conclude that contraction induced by a hyposmotic solution is largely due to Ca(v)1.2 calcium channels although other Ca(2+) influx pathways also contribute.

Increased myogenic responses in uterine but not mesenteric arteries from pregnant offspring of diet-restricted rat dams

Results of epidemiological and animal studies suggest a link between poor in utero growth and cardiovascular disease in adult offspring. Few studies, however, have examined the effects of maternal undernutrition on the vasculature of pregnant female offspring, and to our knowledge, no studies have examined myogenic responses, which are essential to vascular tone development, in these animal models. Thus, myogenic responses were assessed in radial uterine arteries of pregnant female offspring to determine if diet restriction during pregnancy could contribute to transgenerational effects. These results were compared to those in mesenteric arteries, which greatly contribute to peripheral vascular resistance. Myogenic responses in the presence and absence of inhibitors for nitric oxide synthase (NOS) and prostaglandin H synthase (PGHS) were measured in arteries isolated from pregnant, 3-mo-old female offspring of control-fed (C(off)) and globally diet-restricted (DR(off)) rat dams. Although no differences were found in pregnancy weight gain, litter size, or fetal weights, placental size was significantly reduced in DR(off) compared to C(off). Enhanced myogenic reactivity was observed at the highest pressure tested (110 mm Hg) in uterine, but not in mesenteric, arteries from DR(off) compared to C(off). Inhibition of NOS, but not of PGHS, significantly increased myogenic responses in uterine arteries at pressures greater than 80 mm Hg in C(off) but, interestingly, not in DR(off) compared to untreated uterine arteries. Thus, impaired uterine vascular function in diet-restricted pregnant rat dams, which leads to similar impairment in their pregnant offspring, may be a mechanism through which transgenerational effects of unhealthy pregnancies occur.