Effect of pH changes on reactivity of rat mesenteric artery segments at different magnitude of stretch

Voluntary exercise does not increase gastrointestinal motility but increases spatial memory, intestinal eNOS, Akt levels, and Bifidobacteria abundance in the microbiome

The interaction between the gut and brain is a great puzzle since it is mediated by very complex mechanisms. Therefore, the possible interactions of the brain-exercise-intestine-microbiome axis were investigated in a control (C, N = 6) and voluntarily exercised (VE, N = 8) middle-aged rats. The endurance capacity was assessed by VO2max on the treadmill, spatial memory by the Morris maze test, gastrointestinal motility by EMG, the microbiome by 16S RNA gene amplicon sequencing, caveolae by electron microscopy, and biochemical assays were used to measure protein levels and production of reactive oxygen species (ROS). Eight weeks of voluntary running increased VO2max, and spatial memory was assessed by the Morris maze test but did not significantly change the motility of the gastrointestinal tract or production of ROS in the intestine. The protein kinase B (Akt) and endothelial nitric oxide synthase (eNOS) protein levels significantly increased in the intestine, while peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α), mitochondrial transcription factor A (TFAM), nuclear respiratory factor 1 (NFR1), SIRT1, SIRT3, nicotinamide phosphoribosyl transferase (NAMPT), and nuclear factor κB (NF-κB) did not change. On the other hand, voluntary exercise increased the number of caveolae in the smooth muscles of the intestine and relative abundance of Bifidobacteria in the microbiome, which correlated with the Akt levels in the intestine. Voluntary exercise has systemic effects and the relationship between intestinal Akt and the microbiome of the gastrointestinal tract could be an important adaptive response.

The Effects of Acidosis on eNOS in the Systemic Vasculature: A Focus on Early Postnatal Ontogenesis

The activity of many vasomotor signaling pathways strongly depends on extracellular/intracellular pH. Nitric oxide (NO) is one of the most important vasodilators produced by the endothelium. In this review, we present evidence that in most vascular beds of mature mammalian organisms metabolic or respiratory acidosis increases functional endothelial NO-synthase (eNOS) activity, despite the observation that direct effects of low pH on eNOS enzymatic activity are inhibitory. This can be explained by the fact that acidosis increases the activity of signaling pathways that positively regulate eNOS activity. The role of NO in the regulation of vascular tone is greater in early postnatal ontogenesis compared to adulthood. Importantly, in early postnatal ontogenesis acidosis also augments functional eNOS activity and its contribution to the regulation of arterial contractility. Therefore, the effect of acidosis on total peripheral resistance in neonates may be stronger than in adults and can be one of the reasons for an undesirable decrease in blood pressure during neonatal asphyxia. The latter, however, should be proven in future studies.

Paradoxical effects of acidosis on the noradrenaline-induced and neurogenic constriction of the rat tail artery at low temperatures

Although vasodilatation evoked by acidosis at normal body temperature is well known, the reports regarding effect of acidosis on the reactivity of the isolated arteries at low temperatures are nonexistent. This study tested the hypothesis that the inhibitory effect of acidosis on the neurogenic vasoconstriction may be increased by cooling. Using wire myography, we recorded the neurogenic contraction of the rat tail artery segments to the electrical field stimulation in the absence and in the presence of 0.03-10.0 µmol/L noradrenaline. The experiments were conducted at 37 °C or 25 °C and pH 7.4 or 6.6 which was decreased by means of CO₂. Noradrenaline at concentration of 0.03-0.1 µmol/L significantly potentiated the neurogenic vasoconstriction at 25 °C, and the potentiation was not inhibited by acidosis. Contrary to our hypothesis, acidosis at a low temperature did not affect the noradrenaline-induced tone and significantly increased the neurogenic contraction of the artery segments in the absence and presence of noradrenaline. These effects of acidosis were partly dependent on the endothelium and L-type Ca²⁺ channels activation. The phenomenon described for the first time might be of importance for the reduction in the heat loss by virtue of decrease in the subcutaneous blood flow at low ambient temperatures.

The response of the vascular beds to sodium bicarbonate in patients during normothermic bypass

OBJECTIVES

Cardiopulmonary bypass (CPB) provides a unique circumstance to study the effects of drugs on the systemic vasculature. Thus, this study was designed to evaluate the effects of sodium bicarbonate on the systemic circulation during CPB in humans.

DESIGN

Randomized, double-blind study.

SETTING

Tertiary care university hospital.

PARTICIPANTS

Patients presenting for coronary artery bypass graft surgery with CPB.

INTERVENTIONS

In this double-blind study, 22 consecutive adult patients of both sexes undergoing cardiac surgery were randomized into 2 groups. After establishing CPB and cardioplegia, patients in group 1 (n = 11) received saline (0.9%) (1.2 mL/kg), and group 2 received sodium bicarbonate (SB) (7%) (1.2 mL/kg). The blood level in the cardiotomy reservoir, pump flow, and mean arterial pressure were measured for 25 minutes.

MEASUREMENTS AND MAIN RESULTS

The SB-treated patients (group 2) showed significantly greater (p < 0.05) decreases in cardiotomy reservoir blood volume (336 +/- 186 mL) than the saline-treated (140 +/- 97 mL) patients. The mean arterial pressure in group 2 patients significantly (p < 0.05) increased (from 49 +/- 11.9 to 65 +/- 5.3 mmHg) more than in the saline group (from 50 +/- 6.8 to 57 +/- 9.2 mmHg) after 20 minutes. The decrease in reservoir volume significantly (p < 0.05) and inversely correlated (r = -0.61) with the acidotic state of the patients before SB.

CONCLUSIONS

This study found a biphasic response to SB on the systemic circulation during CPB. Early dilation of venous capacitance vessels occurred followed by arteriolar constriction over the 20-minute study interval.

Melatonin-evoked potentiation of the juvenile rat tail artery neurogenic reactivity depends on degree of the change in the reactivity

AIM

Dependence of the melatonin-evoked potentiation of the rat tail artery neurogenic reactivity on degree of the change in the reactivity was studied.

METHOD

Electrical field stimulation-evoked contractile response of the juvenile rat tail artery segment under isometric conditions was recorded. 0.1 mum melatonin was administered after the change in the response produced both spontaneously and by acidification (pH 6.6) or alkalinization (pH 7.8) of the solution.

RESULTS

During the course of experiment, the contraction force continuously declined, being reduced by 12 +/- 5, 24 +/- 7 and 32 +/- 6% at 20, 70, and 170 min after beginning of experiment, respectively. Melatonin applied at these time points increased the contraction by 20 +/- 5, 41 +/- 10, and 48 +/- 8%, respectively, relative to control. This increase in potentiating effect of melatonin during the course of experiment was not because of sensitization of the segment to the hormone. Acidosis-induced considerable decline in neurogenic contraction was counteracted by melatonin, while after alkalosis-induced augmentation in the contraction the hormone was not effective. Melatonin increased the artery response to 0.1 mum noradrenaline.

CONCLUSION

These data suggest that melatonin can restore an attenuated neurogenic reactivity of the juvenile rat tail artery. The effect is more pronounced with further decrease in reactivity and might be due to a change in sensitivity of the post-junctional membrane to noradrenaline.

Mechanism of acidic pH-induced contraction in spontaneously hypertensive rat aorta: role of Ca2+release from the sarcoplasmic reticulum

AIM

This study was conducted to investigate the mechanism of acidic pH-induced contraction (APIC) with regard to Ca2+ handling using isometric tension recording experiments.

RESULTS

Decreasing extracellular pH from 7.4 to 6.5 produced a marked and sustained contraction of spontaneously hypertensive rat (SHR) aorta, that was 128.7 +/- 2.0% of the 64.8 mm KCl-induced contraction. Verapamil, an inhibitor of voltage-dependent Ca2+ channels (VDCC) significantly inhibited the APIC. In Ca2+-deficient solution, sustained contraction induced by acidic pH was abolished completely, while a transient contraction was still observed suggesting the release of Ca2+ from intracellular site. Ryanodine (1 microm), a ryanodine receptor blocker, and 10 microm cyclopiazonic acid (CPA; a sarco/endoplasmic reticulum Ca2+ ATPase inhibitor) abolished the transient contraction induced by acidosis. In normal Ca2+-containing solution, ryanodine significantly decreased the rate of rise as well as maximum level of APIC. Interestingly, ryanodine and CPA showed an additive inhibitory effect with verapamil and the combined treatment of ryanodine or CPA with verapamil nearly abolished the APIC.

CONCLUSIONS

It is concluded that acidic pH induces Ca2+ release from ryanodine/CPA-sensitive store of sarcoplasmic reticulum in SHR aorta. This Ca2+ plays an important role in the facilitation of the rate of rise of APIC, as well as contributing to the sustained contraction via a mechanism which is independent of Ca2+ influx through VDCC.