Microvascular pressure distribution and responses of pulmonary allografts and cheek pouch arterioles in the hamster to oxygen

Effects of hyperoxia on vascular tone in animal models: systematic review and meta-analysis

BACKGROUND

Arterial hyperoxia may induce vasoconstriction and reduce cardiac output, which is particularly undesirable in patients who already have compromised perfusion of vital organs. Due to the inaccessibility of vital organs in humans, vasoconstrictive effects of hyperoxia have primarily been studied in animal models. However, the results of these studies vary substantially. Here, we investigate the variation in magnitude of the hyperoxia effect among studies and explore possible sources of heterogeneity, such as vascular region and animal species.

METHOD

Pubmed and Embase were searched for eligible studies up to November 2017. In vivo and ex vivo animal studies reporting on vascular tone changes induced by local or systemic normobaric hyperoxia were included. Experiments with co-interventions (e.g. disease or endothelium removal) or studies focusing on lung, brain or fetal vasculature or the ductus arteriosus were not included. We extracted data pertaining to species, vascular region, blood vessel characteristics and method of hyperoxia induction. Overall effect sizes were estimated with a standardized mean difference (SMD) random effects model.

RESULTS

We identified a total of 60 studies, which reported data on 67 in vivo and 18 ex vivo experiments. In the in vivo studies, hyperoxia caused vasoconstriction with an SMD of - 1.42 (95% CI - 1.65 to - 1.19). Ex vivo, the overall effect size was SMD - 0.56 (95% CI - 1.09 to - 0.03). Between-study heterogeneity (I2) was high for in vivo (72%, 95% CI 62 to 85%) and ex vivo studies (86%, 95% CI 78 to 98%). In vivo, in comparison to the overall effect size, hyperoxic vasoconstriction was less pronounced in the intestines and skin (P = 0.03) but enhanced in the cremaster muscle region (P < 0.001). Increased constriction was seen in vessels 15-25 μm in diameter. Hyperoxic constriction appeared to be directly proportional to oxygen concentration. For ex vivo studies, heterogeneity could not be explained with subgroup analysis.

CONCLUSION

The effect of hyperoxia on vascular tone is substantially higher in vivo than ex vivo. The magnitude of the constriction is most pronounced in vessels ~ 15-25 μm in diameter and is proportional to the level of hyperoxia. Relatively increased constriction was seen in muscle vasculature, while reduced constriction was seen in the skin and intestines.

Oxygen sensing and signal transduction in hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV), also known as the von Euler-Liljestrand mechanism, is an essential response of the pulmonary vasculature to acute and sustained alveolar hypoxia. During local alveolar hypoxia, HPV matches perfusion to ventilation to maintain optimal arterial oxygenation. In contrast, during global alveolar hypoxia, HPV leads to pulmonary hypertension. The oxygen sensing and signal transduction machinery is located in the pulmonary arterial smooth muscle cells (PASMCs) of the pre-capillary vessels, albeit the physiological response may be modulated in vivo by the endothelium. While factors such as nitric oxide modulate HPV, reactive oxygen species (ROS) have been suggested to act as essential mediators in HPV. ROS may originate from mitochondria and/or NADPH oxidases but the exact oxygen sensing mechanisms, as well as the question of whether increased or decreased ROS cause HPV, are under debate. ROS may induce intracellular calcium increase and subsequent contraction of PASMCs via direct or indirect interactions with protein kinases, phospholipases, sarcoplasmic calcium channels, transient receptor potential channels, voltage-dependent potassium channels and L-type calcium channels, whose relevance may vary under different experimental conditions. Successful identification of factors regulating HPV may allow development of novel therapeutic approaches for conditions of disturbed HPV.

Reduced angiotensin II levels cause generalized vascular dysfunction via oxidant stress in hamster cheek pouch arterioles

OBJECTIVES

We investigated the effect of suppressing plasma angiotensin II (ANG II) levels on arteriolar relaxation in the hamster cheek pouch.

METHODS

Arteriolar diameters were measured via television microscopy during short-term (3-6days) high salt (HS; 4% NaCl) diet and angiotensin converting enzyme (ACE) inhibition with captopril (100mg/kg/day).

RESULTS

ACE inhibition and/or HS diet eliminated endothelium-dependent arteriolar dilation to acetylcholine, endothelium-independent dilation to the NO donor sodium nitroprusside, the prostacyclin analogs carbacyclin and iloprost, and the KATP channel opener cromakalim; and eliminated arteriolar constriction during KATP channel blockade with glibenclamide. Scavenging of superoxide radicals and low dose ANG II infusion (25ng/kg/min, subcutaneous) reduced oxidant stress and restored arteriolar dilation in arterioles of HS-fed hamsters. Vasoconstriction to topically-applied ANG II was unaffected by HS diet while arteriolar responses to elevation of superfusion solution PO2 were unaffected (5% O2, 10% O2) or reduced (21% O2) by HS diet.

CONCLUSIONS

These findings indicate that sustained exposure to low levels of circulating ANG II leads to widespread dysfunction in endothelium-dependent and independent vascular relaxation mechanisms in cheek pouch arterioles by increasing vascular oxidant stress, but does not potentiate O2- or ANG II-induced constriction of arterioles in the distal microcirculation of normotensive hamsters.

Liposomal Vasoactive Intestinal Peptide

Liposomes have been investigated as drug carriers since first discovered in the 1960s. However, the first-generation, so-called classic liposomes found relatively limited therapeutic utility. Nonetheless, the advent in the 1980s of the second-generation sterically stabilized liposomes (SSL) that evade uptake by the host's reticuloendothelial system greatly enhanced their utility as drug carriers because of their prolonged circulation half-life and passive targeting to injured and cancerous tissues. Over the past decade, our work focused on exploiting the bioactivity of vasoactive intestinal peptide (VIP), a ubiquitous 28-amino acid, amphipathic and pleiotropic mammalian neuropeptide, as a drug. To this end, the peptide expresses distinct and unique innate bioactivity that could be harnessed to treat several human diseases that represent unmet medical needs, such as pulmonary hypertension, stroke, Alzheimer's disease, sepsis, female sexual arousal dysfunction, acute lung injury, and arthritis. Unfortunately, the bioactive effects of VIP last only a few minutes due to its rapid degradation and inactivation by enzymes, catalytic antibodies, and spontaneous hydrolysis in biological fluids. Hence, our goal was to develop and test stable, long-acting formulations of VIP using both classic and SSL as platform technologies. We found that spontaneous association of VIP with phospholipid bilayers leads to a transition in the conformation of the peptide from random coil in an aqueous environment to alpha-helix, the preferred conformation for ligand-receptor interactions, in the presence of lipids. This process, in turn, protects VIP from degradation and inactivation and amplifies its bioactivity in vivo. Importantly, we discovered that the film rehydration and extrusion technique is the most suitable to passively load VIP onto SSL at room temperature and yields the most consistent results. Collectively, these attributes indicate that VIP on SSL represents a suitable formulation that could be tested in human disease.

Pressure-induced smooth muscle cell depolarization in pulmonary arteries from control and chronically hypoxic rats does not cause myogenic vasoconstriction

Chronic obstructive pulmonary diseases, as well as prolonged residence at high altitude, can result in generalized airway hypoxia, eliciting an increase in pulmonary vascular resistance. We hypothesized that a portion of the elevated pulmonary vascular resistance following chronic hypoxia (CH) is due to the development of myogenic tone. Isolated, pressurized small pulmonary arteries from control (barometric pressure congruent with 630 Torr) and CH (4 wk, barometric pressure = 380 Torr) rats were loaded with fura 2-AM and perfused with warm (37 degrees C), aerated (21% O(2)-6% CO(2)-balance N(2)) physiological saline solution. Vascular smooth muscle (VSM) intracellular Ca(2+) concentration ([Ca(2+)](i)) and diameter responses to increasing intraluminal pressure were determined. Diameter and VSM cell [Ca(2+)](i) responses to KCl were also determined. In a separate set of experiments, VSM cell membrane potential responses to increasing luminal pressure were determined in arteries from control and CH rats. VSM cell membrane potential in arteries from CH animals was depolarized relative to control at each pressure step. VSM cells from both groups exhibited a further depolarization in response to step increases in intraluminal pressure. However, arteries from both control and CH rats distended passively to increasing intraluminal pressure, and VSM cell [Ca(2+)](i) was not affected. KCl elicited a dose-dependent vasoconstriction that was nearly identical between control and CH groups. Whereas KCl administration resulted in a dose-dependent increase in VSM cell [Ca(2+)](i) in arteries taken from control animals, this stimulus elicited only a slight increase in VSM cell [Ca(2+)](i) in arteries from CH animals. We conclude that the pulmonary circulation of the rat does not demonstrate pressure-induced vasoconstriction.

Effects of peptide molecular mass and PEG chain length on the vasoreactivity of VIP and PACAP(1-38) in pegylated phospholipid micelles

Bioactive properties of certain amphipathic peptides are amplified when self-associated with sterically stabilized micelles (SSM) composed of polyethylene glycol (PEG)-conjugated phospholipids. The purpose of this study was to determine the effects of amphipathic peptide molecular mass and PEG chain length on vasoreactivity evoked by vasoactive intestinal peptide (VIP), a 28-amino acid neuropeptide, and pituitary adenylate cyclase-activating peptide(1-38) (PACAP(1-38)), a 38-amino acid neuropeptide, associated with PEGylated phospholipid micelles in vivo. Both peptides were incubated for 2 h with SSM composed of PEG with molecular mass of 2000 or 5000 grafted onto distearoyl-phosphatidylethanolamine (DSPE-PEG2000 or DSPE-PEG5000) before use. We found that regardless of peptide molecular mass, PEG chain length had no significant effects on peptide-SSM interactions. Using intravital microscopy, VIP associated with DSPE-PEG5000 SSM or DSPE-PEG2000 SSM incubated at 25 degrees C evoked similar vasodilation in the intact hamster cheek pouch microcirculation. Likewise, PACAP(1-38)-induced vasodilation was PEG chain length-independent. However, SSM-associated PACAP(1-38) evoked significantly smaller vasodilation than that evoked by SSM-associated VIP (P < 0.05) at 25 degrees C. When the incubation temperature was increased to 37 degrees C, SSM-associated PACAP(1-38)-induced vasodilation was now similar to that of SSM-associated VIP. This response was associated with a corresponding increase in alpha-helix content of both peptides in the presence of phospholipids. Collectively, these data indicate that for a larger amphipathic peptide, such as PACAP(1-38), greater kinetic energy or longer incubation period is required to optimize peptide-SSM interactions and amplify peptide bioactivity in vivo.

A murine model to study leukocyte rolling and intravascular trafficking in lung microvessels

The cascade of leukocyte interactions under conditions of blood flow is well established in the systemic microcirculation, but not in lung microcirculation. We have developed a murine model to study lung microcirculation by transplanting lung tissue into dorsal skin-fold window chambers in nude mice and examining the ability of leukocytes to traffic within revascularized lung microvessels by intravital microscopy. The revascularized lung allograft demonstrated a network of arterioles, capillaries, and postcapillary venules with continuous blood flow. Stimulation of the lung allograft with TNF-alpha induced leukocyte rolling and adhesion in both arterioles and venules. Treatment with function-blocking anti-selectin mAb revealed that P- and L-selectin are the predominant rolling receptors in the lung microvessels, with E-selectin strengthening P-selectin-dependent interactions. Intravital microscopic studies also demonstrated that during their transit in capillaries, some leukocytes undergo shape change and continue to roll as elongated cells in postcapillary venules. Furthermore, the revascularized microvessels demonstrated the ability to undergo vasoconstriction in response to superfusion with endothelin-1. Overall, these studies demonstrate that the revascularized lung allograft is responsive to various external stimuli such as cytokines and vaso-active mediators and serves as a model to evaluate the interaction of leukocytes with the vascular endothelium in the lung microcirculation under acute as well as chronic experimental conditions.

Phospholipids modulate the biophysical properties and vasoactivity of PACAP-(1--38)

The purpose of this study was to elucidate the interactions between pituitary adenylate cyclase-activating peptide (PACAP)-(1--38) and phospholipids in vitro and to determine whether these phenomena modulate, in part, the vasorelaxant effects of the peptide in the intact peripheral microcirculation. We found that the critical micellar concentration of PACAP-(1--38) was 0.4-0.9 microM. PACAP-(1--38) significantly increased the surface tension of a dipalmitoylphosphatidylcholine monolayer and underwent conformational transition from predominantly random coil in saline to alpha-helix in the presence of distearoyl-phosphatidylethanolamine-polyethylene glycol (molecular mass of 2,000 Da) sterically stabilized phospholipid micelles (SSM) (P < 0.05). Using intravital microscopy, we found that aqueous PACAP-(1--38) evoked significant concentration-dependent vasodilation in the intact hamster cheek pouch that was significantly potentiated when PACAP-(1--38) was associated with SSM (P < 0.05). The vasorelaxant effects of aqueous PACAP-(1--38) were mediated predominantly by PACAP type 1 (PAC(1)) receptors, whereas those of PACAP-(1--38) in SSM predominantly by PACAP/vasoactive intestinal peptide type 1 and 2 (VPAC(1)/VPAC(2)) receptors. Collectively, these data indicate that PACAP-(1--38) self-associates and interacts avidly with phospholipids in vitro and that these phenomena amplify peptide vasoactivity in the intact peripheral microcirculation.

Acute and chronic treatment with nicotine impairs reactivity of arterioles in response to activation of potassium channels

Although acute and chronic treatment with nicotine impairs nitric oxide synthase-dependent responses of large and small blood vessels, the effect of nicotine on other vasodilator pathways remains uncertain. The goal of the current study was to determine effects of nicotine on dilatation of arterioles to activation of ATP-sensitive potassium channels. Reactivity of cheek pouch arterioles ( approximately 50 microm) was measured during acute (1-2 h) and chronic (2-to 3-week) exposure to nicotine in response to aprikalim, cromakalim, and nitroglycerin. Acute treatment with nicotine impaired dilatation of arterioles in response to aprikalim and cromakalim but not nitroglycerin. Aprikalim and cromakalim (1.0 microM) dilated arterioles by 37 +/- 5% and 30 +/- 3%, respectively, before, but by only 21 +/- 4% and 16 +/- 3%, respectively, after infusion of nicotine (p < 0.05). Chronic exposure to nicotine did not alter vasodilatation to nitroglycerin but impaired vasodilatation to aprikalim and cromakalim. In vehicle-treated hamsters, aprikalim and cromakalim (1.0 microM) dilated arterioles by 28 +/- 1% and 32 +/- 3%, respectively. However, in nicotine-treated hamsters aprikalim and cromakalim (1.0 microM) dilated arterioles by only 3 +/- 1% and 13 +/- 1%, respectively. Next, the role of superoxide anion in impaired responses of arterioles to aprikalim and cromakalim during acute infusion of nicotine was examined. Treatment with superoxide dismutase attenuated the effects of nicotine on aprikalim and cromakalim. Thus, acute and chronic exposure to nicotine has profound affects on vasodilatation to activation of ATP-sensitive potassium channels, which may be mediated by superoxide anion.

Force-velocity relationship of myogenically active arterioles

We compared the shortening velocity of smooth muscle in arterioles that had low or high levels of myogenic tone or norepinephrine (NE)-induced tone. We hypothesized that enhanced myogenic tone of arterioles reflects an enhanced maximum velocity of shortening of arteriolar smooth muscle in a way that is different from that produced by NE. These concepts are untested assumptions of arteriolar mechanics. Second-order arterioles from hamster cheek pouch (passive diameter at 40 mmHg = 42 microm) were isolated and cannulated for in vitro study. In the absence of flow, pressure was controlled by hydraulic pumps so that servo control of wall tension could be achieved from measurement of internal diameter and pressure. Isotonic quick-release protocols were used to measure the initial velocity of shortening following release from control wall tension (afterload) to a series of fractional afterloads. After release, the initial rates of shortening were fit to the Hill equation to obtain coefficients for a hyperbolic fit of the velocity-afterload relationship. The maximal unloaded shortening velocity for partially activated arterioles (V'(max)) was determined from the y-intercept of each plot. Using this procedure, we compared V'(max) from two groups of arterioles equilibrated at low or high pressure, i.e., with low or high myogenic tone. Arterioles with higher myogenic tone had higher values of V'(max) than arterioles with lower myogenic tone. V'(max) for arterioles partially activated with NE at low pressure was comparable to V'(max) for arterioles with high myogenic tone, but NE produced high velocities at low force, whereas enhanced myogenic tone produced roughly parallel shifts in velocity and force. The results suggest that increased myogenic tone does indeed reflect enhanced activation of arteriolar smooth muscle, and this effect is mechanically different from that produced by NE.

Tyrosine kinase inhibitors modulate agonist-induced vasodilation in the hamster cheek pouch

The purpose of this study was to determine whether inhibitors of tyrosine kinase attenuate vasodilation elicited by endogenously elaborated and exogenously applied nitric oxide in the in situ peripheral microcirculation. Using intravital microscopy, we found that pretreatment with genistein (1.0 microM) and tyrphostin 25 (10.0 microM), two structurally unrelated tyrosine kinase inhibitors, significantly attenuated acetylcholine-, bradykinin- and nitroglycerin-induced dilation of second-order arterioles (51 +/- 1 microm) in the in situ hamster cheek pouch (P < 0.05). Both inhibitors nearly abrogated acetylcholine-induced responses but only partially blocked bradykinin- and nitroglycerin-induced vasodilation. Genistein and tyrphostin 25 alone had no significant effects on resting arteriolar diameter and on adenosine-induced vasodilation in the cheek pouch. On balance, these data indicate that tyrosine kinase inhibitors attenuate endogenously elaborated and exogenously applied nitric oxide-induced vasodilation in the in situ hamster cheek pouch. However, the extent of tyrosine kinase inhibitor-sensitive pathway involvement in this response appears to be agonist dependent.

Constrictor responses of resistance arterioles during diabetes mellitus

While diabetes mellitus appears to alter nitric oxide synthase-dependent vasodilatation, the effect of diabetes on constrictor responses of resistance arterioles is not clear. Our goal was to examine the effect of diabetes on constrictor responses of cheek pouch arterioles. In vivo diameter of arterioles ( approximately 50 microm) was measured in response to norepinephrine, the thromboxane analogue (U-46619) and endothelin-1 in nondiabetic and diabetic hamsters (4-6 weeks post streptozotocin). Norepinephrine (1.0 and 10 nM) and U-46619 (0.1 and 1.0 nM) produced similar dose-related vasoconstriction in nondiabetic and diabetic hamsters (P > 0.05). In contrast, vasoconstriction to endothelin-1 (0.1 and 1.0 pM) was greater in diabetic than nondiabetic hamsters (P < 0.05). Next, we examined the role of nitric oxide in basal vascular tone and whether enhanced vasoconstriction in diabetic hamsters to endothelin-1 might be related to an alteration in the modulatory role of nitric oxide. N(G)-monomethyl-L-arginine (L-NMMA) (1.0, 10 and 100 microM) produced dose-related vasoconstriction in nondiabetic, but not diabetic hamsters. Further, L-NMMA did not alter vasoconstriction in response to endothelin-1 in nondiabetic and diabetic hamsters. These findings suggest that diabetes alters constriction of cheek pouch resistance arterioles to endothelin-1 which appears to be independent of the synthesis/release of nitric oxide. In addition, based upon findings using L-NMMA, it appears that there is a reduced influence of nitric oxide on basal diameter of resistance arterioles during diabetes.

Chronic exposure to nicotine alters endothelium-dependent arteriolar dilatation: effect of superoxide dismutase

The first goal of this study was to determine whether chronic injection of nicotine alters endothelium-dependent arteriolar dilatation. We measured the diameter of cheek pouch resistance arterioles (approximately 50 microm in diameter) in response to endothelium-dependent (acetylcholine and ADP) and -independent (nitroglycerin) agonists in control hamsters and hamsters treated with nicotine (2 microg. kg-1. day-1 for 2-3 wk). In control hamsters, acetylcholine (0.1 and 1.0 microM) dilated arterioles by 13 +/- 2 and 31 +/- 3%, respectively, and ADP (1.0 and 10 microM) dilated arterioles by 18 +/- 1 and 30 +/- 1%, respectively. In contrast, acetylcholine (0.1 and 1.0 microM) dilated arterioles by only 5 +/- 2 and 12 +/- 3%, respectively, and ADP (1.0 and 10 microM) dilated arterioles by only 7 +/- 2 and 13 +/- 3%, respectively, in animals treated with nicotine (P < 0.05 vs. response in control hamsters). Nitroglycerin produced similar dose-related dilatation of cheek pouch arterioles in control and nicotine-treated hamsters. Our second goal was to examine a possible mechanism for impaired endothelium-dependent arteriolar dilatation during chronic treatment with nicotine. We found that superfusion of the cheek pouch microcirculation with superoxide dismutase (150 U/ml) restored impaired endothelium-dependent, but did not alter endothelium-independent, arteriolar dilatation in hamsters treated with nicotine. Superfusion with superoxide dismutase did not alter endothelium-dependent or -independent arteriolar dilatation in control hamsters. We suggest that chronic exposure to nicotine produces selective impairment of endothelium-dependent arteriolar dilatation via a mechanism related to the synthesis/release of oxygen-derived free radicals.

Acute infusion of nicotine potentiates norepinephrine-induced vasoconstriction in the hamster cheek pouch

Although cigarette smoking and the components of cigarette smoke appear to alter nitric oxide synthase-dependent dilation of blood vessels, the effect of these substances on constrictor responses of resistance arterioles has not been examined. Thus the goal of this study was to examine the effect of a major component of cigarette smoke-that is, nicotine-on constrictor responses of cheek pouch arterioles. The diameter of cheek pouch arterioles (approximately 50 microm in diameter) was measured by using intravital microscopy. We examined the responses of arterioles to angiotensin II, arginine vasopressin, norepinephrine, and the thromboxane analog U-46619 before and after treatment with vehicle (saline solution), N(G)-monomethyl-L-arginine (L-NMMA; 1.0 micromol/L), or nicotine (2.0 microg/kg/min i.v. for 30 minutes followed by a maintenance dose of 0.35 microg/kg/min for 30 minutes). Topical application of angiotensin II (0.01 and 0.1 nmol/L), arginine vasopressin (1.0 and 10 pmol/L), norepinephrine (1.0 and 10 nmol/L), and U-46619 (0.01 and 0.1 nmol/L) produced marked reproducible constriction of cheek pouch arterioles in hamsters treated with vehicle. Topical application of L-NMMA potentiated constrictor responses of arterioles to the high dose of arginine vasopressin (28%+/-4% versus 36%+/-4%; P<.05) and to both doses of norepinephrine (14%+/-1% and 24%+/-2% versus 19%+/-1% and 31%+/-3%; P<.05). The infusion of nicotine did not alter responses to angiotensin II, arginine vasopressin, or U-46619 but modestly potentiated vasoconstriction in response to norepinephrine (12%+/-2% and 22%+/-2% versus 14%+/-2% and 26%+/-2%; P<.05). These findings suggest that the synthesis/release of nitric oxide may modulate constrictor responses of cheek pouch resistance arterioles to selected agonists. In addition, nicotine, at levels observed in smokers, may potentiate norepinephrine-induced vasoconstriction. We suggest that preservation/potentiation of vasoconstrictor responses may contribute to the pathogenesis of vascular abnormalities associated with cigarette smoking.

Superoxide dismutase restores endothelium-dependent arteriolar dilatation during acute infusion of nicotine

We previously showed [Am. J. Physiol. 272 (Heart Circ. Physiol. 41): H2337-H2342, 1997] that nicotine impairs endothelium-dependent arteriolar dilatation. However, mechanisms that accounted for the effect of nicotine on endothelium-dependent vasodilatation were not examined. Thus the goal of this study was to examine the role of oxygen radicals in nicotine-induced impairment of arteriolar reactivity. We measured diameter of cheek pouch resistance arterioles (approximately 50 micrometer diameter) in response to endothelium-dependent (ACh and ADP) and -independent (nitroglycerin) agonists before and after infusion of vehicle or nicotine in the absence or presence of superoxide dismutase. ACh, ADP, and nitroglycerin produced dose-related dilatation of cheek pouch arterioles before infusion of vehicle or nicotine. Infusion of vehicle, in the absence or presence of superoxide dismutase (150 U/ml), did not alter endothelium-dependent or -independent arteriolar dilatation. In contrast, infusion of nicotine (2 microgram . kg-1 . min-1) impaired endothelium-dependent, but not -independent, arteriolar dilatation. In addition, the effect of nicotine on endothelium-dependent vasodilatation was reversed by topical application of superoxide dismutase. We suggest that nicotine impairs endothelium-dependent arteriolar dilatation via an increase in the synthesis/release of oxygen-derived free radicals.

Effect of cigarette smoke extract on arteriolar dilatation in vivo

The goal of this study was to determine whether cigarette smoke extract alters dilatation of arterioles in vivo in response to agonists that produce activation of ATP-sensitive potassium channels and activation of adenylate cyclase. By using intravital microscopy, we measured diameter of arterioles contained within the microcirculation of the hamster cheek pouch during suffusion with agonists in the absence and presence of cigarette smoke extract (0.1, 0.5, and 1.0%). Before treatment with cigarette smoke extract, activation of ATP-sensitive potassium channels with aprikalim and cromakalim produced dose-related dilatation of cheek pouch arterioles. Similarly, activation of adenylate cyclase with isoproterenol and forskolin produced dose-related dilatation of cheek pouch arterioles before treatment with cigarette smoke extract. Superfusion of 0.1% cigarette smoke extract did not change baseline diameter of arterioles and did not alter responses of cheek pouch arterioles to activation of ATP-sensitive potassium channels and adenylate cyclase. Superfusion of 0.5 and 1.0% cigarette smoke extract also did not alter baseline diameter of arterioles but did impair dilatation of arterioles in response to activation of ATP-sensitive potassium channels and adenylate cyclase. These findings suggest that cigarette smoke extract impairs dilatation of resistance arterioles in response to activation of important cellular dilator pathways.

Encapsulation of vasoactive intestinal peptide into liposomes: effects on vasodilation in vivo

The purpose of this study was to determine whether encapsulation of vasoactive intestinal peptide (VIP) into liposomes potentiated its vasorelaxant effects in vivo. Using intravital microscopy, we measured the diameter of second-order arterioles (53 +/- 1 microns) in the hamster cheek pouch before, during and after suffusion of VIP, liposomes and VIP encapsulated into liposomes for 7 min. We found that VIP (0.05, 0.1 & 1.0 nmol) induced significant, time- and concentration-dependent vasodilation (9 +/- 1%, 13 +/- 3% and 14 +/- 1% increase from baseline values, respectively; mean +/- SEM; n = 12; p < 0.05). Arteriolar diameter returned to baseline values within 1-4 min after suffusion was stopped. These effects were significantly potentiated when VIP (0.05, 0.1 & 1.0 nmol) was encapsulated into liposomes (26 +/- 6%, 38 +/- 7% and 34 +/- 3% increase from baseline values, respectively; n = 12; p < 0.05). In addition, arteriolar diameter returned to baseline values 5-13 min after suffusion was stopped. Suffusion of liposomes alone had no significant effects on arteriolar diameter (n = 12; p > 0.5). We conclude that encapsulation of VIP into liposomes potentiates and prolongs of its vasorelaxant effects in the peripheral microcirculation in vivo.

Morphological study of bovine lung grafted into the hamster cheek pouch

The hamster cheek pouch has been used extensively to study the modulation of microvascular responsiveness of native and transplanted tissues, because it is immunologically privileged. The purpose of this study was to determine the structural changes that occur over time in bovine lung tissue (donor) that was grafted into the hamster cheek pouch (recipient). Lungs from adult cows were cut into 1-mm-thick slices and grafted into the cheek pouch of adult Syrian golden hamsters (n = 60). After induction of anesthesia, bovine lung tissue was placed under the avascular tissue covering the cheek pouch, and the overlying skin was sutured. Intravital microscopy (IM) and transmission electron microscopy (TEM) of the cheek pouch and grafted tissue were performed 1, 7, 14, and 28 days after grafting. By using IM, we found blood flow throughout the grafted bovine lung tissue between days 7 and 14 post-transplantation. Both IM and TEM showed that the grafted tissue contained patent microvessels anastomosing with cheek pouch microvessels, alveolar structures, and interstitial tissue. Mast cell infiltration around microvessels of the grafted tissue was evident in all animals between days 14 and 28 post-grafting. No other inflammatory cells were identified throughout the observation period. By day 28 post-grafting, the entire lung tissue became fibrotic. We conclude that bovine lung tissue can be successfully transplanted into the hamster cheek pouch, that blood flow is established throughout the graft, and that prominent mast cell infiltration is associated with fibrosis of the graft 28 days after transplantation. We suggest that this model can be useful in studying pulmonary microvascular responses in situ.

Specificity of arginine vasopressin and angiotensin II for microvessels in the hamster cheek pouch after the induction of renovascular hypertension

The present study was undertaken to determine the specificity of the vasoconstrictor activity to angiotensin II (AII) and arginine vasopressin (AVP) on the microcirculation in normal and renovascular hypertensive states. Ten to fourteen days after the induction of hypertension, Syrian hamsters were anesthetized with pentobarbital sodium, the cheek pouch was exposed, and a plastic chamber was placed in situ so the membrane could be suffused with bicarbonate-buffered Ringer's solution (5% CO2, 95% N2, pH 7.4). Third order arterioles (30-45 micron) were identified for study and vessel diameter was measured using a shearing device. In one group of normotensive and hypertensive hamsters, AII was microapplied to the arteriole before and after adding an AVP antagonist to the suffusate. In a second group of similar hamsters, AVP was microapplied to the arteriole before and after adding an angiotensin II blocker, saralasin acetate, to the suffusate. AVP and AII receptor blockade was documented by observing whether the vasoconstrictor effect of either AVP or AII was abolished. Dose-response curves for either peptide were not altered in the presence of the antagonist to the other peptide; however, they were shifted to the left in the RHT hamsters. Neither AVP nor AII receptor blockade altered control resting arteriolar diameters. Thus, it can be concluded that the microvascular response to both AII and AVP are potentiated in RHT and there are no interactions between either AII or AVP with the receptors of the other peptide in these microvessels in normal or RHT hamsters, indicating a high specificity for each peptide to its vascular receptor.

Comparative morphology and evolution of cheek pouches in rodents

There are two types of cheek pouches in extant rodents. Internal cheek pouches are evaginations of the oral cavity deep to M. platysma and M. sphincter colli profundus, and have evolved independently in some species of the superfamilies Sciuroidea and Muroidea. External, furlined cheek pouches open lateral to and separate from the oral cavity, (also deep to M. platysma and M. sphincter colli profundus), and occur in all species of the families Geomyidae and Heteromyidae. The presence of external, furlined cheek pouches is a synapomorphy for the superfamily Geomyoidea. The posterior retractor muscle of the pouch is derived from facial musculature in sciurids, from trapezius musculature in cricetids, and from both facial and trapezius muscle groups in the Geomyoidea. Differences also exist in the musculature associated with the pouch opening. In the Sciuridae and Cricetidae, the M. buccinatorius muscle group acts as a sphincter to control the size of the pouch opening. In the Geomyoidea, the size of the opening is controlled by the M. orbicularis sacculi in concert with a slip of the M. platysma myoides. Thin sections and scanning electron micrographs of the pouch tissue reveal the presence of dermal papillae in Phodopus sungorus but not in a close relative, Mesocricetus auratus. All members of the subfamily Cricetinae have a peninsula of highly folded tissue projecting anteriorly from the posteromedial pouch wall. This folding allows for expansion of the pouch walls when food is stored in the pouch.

The site and mechanism of oxygen sensing for the pulmonary vessels

Lung vessels are unique in the body in that they react to hypoxia with constriction rather than dilatation. Whether this characteristic is inherent in the lung vessel or is due to an influence from a sensor in the surrounding lung parenchyma is not resolved. Recent data, however, showing that vascular hypoxia as well as airway hypoxia can produce pulmonary vasoconstriction and that the sensor for alveolar hypoxia is upstream in the precapillary vessels, allows but does not prove the precapillary pulmonary artery itself to be the O2 sensor. In addition, with the elimination of the mast cell as a necessary extravascular sensor for hypoxia at least in the mouse, there is no good candidate for an extravascular sensor for hypoxic pulmonary vasoconstriction.

Mechanics of smooth muscle in isolated single microvessels

In vivo studies on frog mesenteric arterioles (4) indicate that segmental differences in the response of microvessels to physical and chemical stimuli can be explained simply in terms of the length-tension characteristics of vascular smooth muscle at different points along the vascular tree. Studies on single, isolated arterioles in vitro were initiated to examine more closely the validity of this explanation for regional response differences. This paper reports some of the results. First-, second-, and third-order arterioles (18-60 micron i.d.) were dissected from hamster cheek pouches. The vessels were cannulated with a modified Burg microperfusion system, and their mechanical properties studied using the methods described by Duling and Gore. Vessels were activated in four stages with K+ and norepinephrine. During activation, transmural pressures were adjusted to minimize vascular smooth-muscle shortening. Active pressure-diameter curves were recorded while adjusting transmural pressure through the range 5 to 400 cm H20 in 5-25 cm steps. Vessel dimensions were measured with a videomicrometer. Passive curves were obtained after equilibration overnight in Ca2+-free medium. The vessels were then fixed and prepared for histologic sectioning, and measurements of vessel-wall composition were made. The Laplace relationship was used to construct length-tension diagrams, and the histologic data were used to normalize the dimensional data to smooth-muscle lengths. Maximum active tension of second-order arterioles (1,170 dynes/cm) was two times previous values reported by Gore et al. This was due presumably to refinements in techniques and dissection procedures. Maximum active stress averaged 3.9 X 10(+6) dynes/cm2 for second-order arterioles. This number is identical to data obtained from hog carotid strips by Dillon et al.