Pig Mesenteric Artery Research Articles

Development of a Simple In Vitro Artery Model and an Evaluation of the Impact of Pulsed Flow on High-Intensity Focused Ultrasound Ablation

BackgroundMany parameters have to be investigated before an optimal strategy for thermal therapies can be defined. Such studies are limited by the number of animals that may be included and by the difficulties in the use of isolated perfused organs. Realistic in vitro anthropomorphic vascular phantoms have been suggested and are based on the use of agar or silicone but not on biological tissues. More simply, biological and reliable models can be developed to mimic the behavior of arteries under perfusion. Material and methodsChicken esophagus was used since it reproduces both the anatomical and the mechanical local properties of a 5-mm-diameter artery. The esophagus was placed inside a bovine liver and connected to polyurethane tubes. The flow was driven using two pumps and a solenoid to mimic pulsed flow and the cardiac valve. The blood was mimicked using degassed water and 50-μm silica beads at a concentration of 40 mg/L. The Doppler signals used as a reference to validate the in vitro artery model were acquired during an animal study. Using a high-intensity focused ultrasound (HIFU) device, several HIFU lesions were created in vitro in liver samples with the artery mimic model placed at different depths. ResultsThe waveforms of in vivo and in vitro Doppler signals had a cycle length of 1.09 s and 1.10 s, respectively, corresponding to 55 beats per minute (bpm). The average peak flow rate was 25.3 cm/s for in vivo waveforms and 27.8 cm/s for in vitro waveforms. The relative distension of the in vitro artery mimic (10%) was similar to that measured in pig mesenteric arteries and representative of human artery compliance. The dimensions of HIFU lesions were different depending on the location of the artery mimic. ConclusionsA simple and reliable model of arteries is described. This model reproduced both the geometrical and the mechanical local properties of an artery. The flow profile, the flow rate and compliant behavior were found to be similar to those that can be recorded in vivo. This model can be used to evaluate the potential perfusion effects when developing devices for thermal therapies.

Diverse Kir expression contributes to distinct bimodal distribution of resting potentials and vasotone responses of arterioles.

The resting membrane potential (RP) of vascular smooth muscle cells (VSMCs) is a major determinant of cytosolic calcium concentration and vascular tone. The heterogeneity of RPs and its underlying mechanism among different vascular beds remain poorly understood. We compared the RPs and vasomotion properties between the guinea pig spiral modiolar artery (SMA), brain arterioles (BA) and mesenteric arteries (MA). We found: 1) RPs showed a robust bimodal distribution peaked at -76 and -40 mV evenly in the SMA, unevenly at -77 and -51 mV in the BA and ~-71 and -52 mV in the MA. Ba2+ 0.1 mM eliminated their high RP peaks ~-75 mV. 2) Cells with low RP (~-45 mV) hyperpolarized in response to 10 mM extracellular K+, while cells with a high RP depolarized, and cells with intermediate RP (~-58 mV) displayed an initial hyperpolarization followed by prolonged depolarization. Moderate high K+ typically induced dilation, constriction and a dilation followed by constriction in the SMA, MA and BA, respectively. 3) Boltzmann-fit analysis of the Ba2+-sensitive inward rectifier K+ (Kir) whole-cell current showed that the maximum Kir conductance density significantly differed among the vessels, and the half-activation voltage was significantly more negative in the MA. 4) Corresponding to the whole-cell data, computational modeling simulated the three RP distribution patterns and the dynamics of RP changes obtained experimentally, including the regenerative swift shifts between the two RP levels after reaching a threshold. 5) Molecular works revealed strong Kir2.1 and Kir2.2 transcripts and Kir2.1 immunolabeling in all 3 vessels, while Kir2.3 and Kir2.4 transcript levels varied. We conclude that a dense expression of functional Kir2.X channels underlies the more negative RPs in endothelial cells and a subset of VSMC in these arterioles, and the heterogeneous Kir function is primarily responsible for the distinct bimodal RPs among these arterioles. The fast Kir-based regenerative shifts between two RP states could form a critical mechanism for conduction/spread of vasomotion along the arteriole axis.

Effects of pregnancy and chronic hypoxia on contractile responsiveness to alpha1-adrenergic stimulation.

Decreased contractile response to vasoconstrictors in uterine and nonuterine vessels contributes to increased blood flow to the uterine circulation during normal pregnancy. Pregnancies complicated by preeclampsia and/or chronic hypoxia show a reversal or diminution of these pregnancy-associated changes. We sought to determine whether chronic hypoxia opposes the reduction in contractile response in uterine and nonuterine vessels during normal pregnancy and, if so, whether decreased basal nitric oxide (NO) activity was involved. We examined the contractile response to phenylephrine (PE) in guinea pig uterine artery (UA), mesenteric artery (MA), and thoracic aorta (TA) rings isolated from nonpregnant or pregnant guinea pigs that had been exposed throughout gestation to either low (1,600 m, n = 47) or high (3,962 m, n = 43) altitude. In the UA, pregnancy reduced contractile sensitivity to PE and did so similarly at low and high altitude (EC50: 4.0 x 10(-8) nonpregnant, 9.3 x 10(-8) pregnant at low altitude; 4.8 x 10(-8) nonpregnant, 1.0 x10(-8) pregnant at high altitude; both P < 0.05). Addition of the NO synthase inhibitor nitro-L-arginine (NLA; 200 mM) to the vessel bath increased contractile sensitivity in the pregnant UA (P < 0.05) and eliminated the effect of pregnancy at both altitutes. NLA also raised contractile sensitivity in the nonpregnant high-altitude UA, but contractile response without NLA did not differ in the high- and low-altitude animals. In the MA, pregnancy decreased contractile sensitivity to PE at high altitude only, and this shift was reversed by NO inhibition. In the TA, neither pregnancy nor altitude affected contractile response, but NO inhibition raised contractile response in nonpregnant and pregnant TA at both altitudes. We concluded that pregnancy diminished contractile response to PE in the UA, likely as a result of increased NO activity, and that these changes were similar at low and high altitude. Counter to our hypothesis, chronic hypoxia did not diminish the pregnancy-associated reduction in contractile sensitivity to PE or inhibit basal NO activity in the UA; rather it enhanced, not diminished, basal NO activity in the nonpregnant UA and the pregnant MA.

Spontaneous Electrical Activity in Pressurized Small Mesenteric Arteries

Spontaneous electrical activity was recorded intracellularly in vitro from smooth muscle cells of guinea pig small pressurized mesenteric arteries. Spontaneous action potentials were recorded at 37 degrees C at frequencies of 30-55/min. Each action potential consisted of a prepotential (pacemaker potential) followed by a spike of variable amplitude (10-35 mV). This activity was not blocked by tetrodotoxin (TTX) or guanethidine, indicating it was myogenic in origin. Sympathetic nerve stimulation (single 0.5-ms field stimuli) could evoke action potentials in between the spontaneous action potentials and could drive the activity, this effect was blocked by TTX. Addition of the vasodilator adenosine (10(-6) to 10(-4) M) reversibly decreased action potential amplitude and frequency. Lowering the temperature to 35 degrees C for 1-3 min during a single impalement decreased spontaneous action potential frequency. Spontaneous activity was abolished after longer periods at 35 degrees C. The spontaneous activity recorded in vitro at 37 degrees C and 5 or 40 mm Hg inflation pressure was similar to that previously reported from guinea pig and rat mesenteric arteries in vivo. Such activity might be important in the normal physiological control of arterial tone.

Arterial walls are protected against deposition of platelet thrombi by a substance (prostaglandin X) which they make from prostaglandin endoperoxides

Prostaglandin (PG) endoperoxides (PGG 2 and PGH 2) contract arterial smooth muscle and cause platelet aggregation. Microsomes from pig aorta, pig mesenteric arteries, rabbit aorta and rat stomach fundus enzymically transform PG endoperoxides to an unstable product (PGX) which relaxes arterial strips and prevents platelet aggregation. Microsomes from rat stomach corpus, rat liver, rabbit lungs, rabbit spleen, rabbit brain, rabbit kidney medulla, ram seminal vesicles as well as particulate fractions of rat skin homogenates transform PG endoperoxides to PGE- and PGF- rather than to PGX-like activity. PGX differs from the products of enzymic transformation of prostaglandin endoperoxides so far identified, including PGE 2, F 2α, D 2, thromboxane A 2 and their metabolites. PGX is less active in contracting rat fundic strip, chick rectum, guinea pig ileum and guinea pig trachea than are PGG 2 and PGH 2. PGX does not contract the rat colon. PGX is unstable in aqueous solution and its anti-aggregating activity disappears within 0.25 min on boiling or within 10 min at 37° C. As an inhibitor of human platelet aggregation induced in vitro by arachidonic acid PGX was 30 times more potent than PGE 1. The enzymic formation of PGX is inhibited by 15-hydroperoxy arachidonic acid (IC 50 = 0.48 μg/ml), by spontaneously oxidised arachidonic acid (IC 50 <100 μg/ml) and by tranylcypromine (IC 50 = 160 μg/ml). We conclude that a balance between formation by arterial walls of PGX which prevents platelet aggregation and release by blood platelets of prostaglandin endoperoxides which induce aggregation is of the utmost importance for the control of thrombus formation in vessels.