The effect of long-term hypoxia on tension and intracellular calcium responses following stimulation of the thromboxane A(2) receptor in the left anterior descending coronary artery of fetal sheep

Perinatal hypoxia augments contractile impact of NADPH oxidase-derived ROS in early postnatal rat arteries

BACKGROUND

 Reactive oxygen species (ROS), including those produced by NADPH oxidase (NOX), play an important vasomotor role, especially at early postnatal period. Mechanisms for regulating vascular tone can change significantly due to neonatal asphyxia and accompanying hypoxia. We tested the hypothesis that normobaric hypoxia (8% O2) for 2 h at the second day of life changes the functional contribution of NOX-derived ROS to the regulation of agonist-induced contraction in early postnatal rats.

METHODS

We studied saphenous arteries from 11- to 14-day-old male offspring using isometric myography and Western blotting and assessed the content of biochemical parameters in blood serum.

RESULTS

 The values of main biochemical parameters in blood serum and the protein content of NOXs and superoxide dismutases in arterial tissue did not differ between "Control" and "Hypoxia" pups. The NOX inhibitor VAS2870 equally reduced the contractile responses of arteries to α1-adrenoceptor agonist methoxamine in "Control" and "Hypoxia" pups, but its effect was more pronounced in the arteries from "Hypoxia" pups when vasocontraction was evoked by the agonist of thromboxane A2 receptors U46619.

CONCLUSION

 Perinatal hypoxia at the second day of life increases procontractile influence of NOX-derived ROS to the regulation of U46619-induced vasocontraction in the systemic arteries at early postnatal ontogenesis.

IMPACT

Nothing is known about programming effects of perinatal hypoxia, including birth asphyxia, on the ROS-mediated regulation of contraction in systemic arteries of early postnatal organism. 2-h normobaric hypoxia (8% O2) in rats at the second day of life increases the procontractile contribution of NOX-produced ROS to the regulation of U46619-induced vasocontraction in the systemic arteries at early postnatal ontogenesis. This fact may serve as a risk factor for the development of various disorders at later developmental stages and should be considered regarding the therapy for newborns who have suffered neonatal asphyxia.

Pressure-dependent contribution of Rho kinase-mediated calcium sensitization in serotonin-evoked vasoconstriction of rat cerebral arteries

Our understanding of the cellular signalling mechanisms contributing to agonist-induced constriction is almost exclusively based on the study of conduit arteries. Resistance arteries/arterioles have received less attention as standard biochemical approaches lack the necessary sensitivity to permit quantification of phosphoprotein levels in these small vessels. Here, we have employed a novel, highly sensitive Western blotting method to assess: (1) the contribution of Ca(2+) sensitization mediated by phosphorylation of myosin light chain phosphatase targeting subunit 1 (MYPT1) and the 17 kDa PKC-potentiated protein phosphatase 1 inhibitor protein (CPI-17) to serotonin (5-HT)-induced constriction of rat middle cerebral arteries, and (2) whether there is any interplay between pressure-induced myogenic and agonist-induced mechanisms of vasoconstriction. Arterial diameter and levels of MYPT1 (T697 and T855), CPI-17 and 20 kDa myosin light chain subunit (LC(20)) phosphorylation were determined following treatment with 5-HT (1 micromol l(1)) at 10 or 60 mmHg in the absence and presence of H1152 or GF109203X to suppress the activity of Rho-associated kinase (ROK) and protein kinase C (PKC), respectively. Although H1152 and GF109203X suppressed 5-HT-induced constriction and reduced phospho-LC(20) content at 10 mmHg, we failed to detect any increase in MYPT1 or CPI-17 phosphorylation. In contrast, an increase in MYPT1-T697 and MYPT1-T855 phosphorylation, but not phospho-CPI-17 content, was apparent at 60 mmHg following exposure to 5-HT, and the phosphorylation of both MYPT1 sites was sensitive to H1152 inhibition of ROK. The involvement of MYPT1 phosphorylation in the response to 5-HT at 60 mmHg was not dependent on force generation per se, as inhibition of cross-bridge cycling with blebbistatin (10 micromol l(1)) did not affect phosphoprotein content. Taken together, the data indicate that Ca(2+) sensitization owing to ROK-mediated phosphorylation of MYPT1 contributes to 5-HT-evoked vasoconstriction only in the presence of pressure-induced myogenic activation. These findings provide novel evidence of an interplay between myogenic- and agonist-induced vasoconstriction in cerebral resistance arteries.