Adaptations of the endothelin system after exercise training in a porcine model of ischemic heart disease

Enhanced KCl-mediated contractility and Ca2+ sensitization in porcine collateral-dependent coronary arteries persist after exercise training

We have previously reported enhanced Ca²⁺ sensitivity of coronary arteries that is dependent upon collateral circulation for their blood supply. For the current study, we hypothesized that small collateral-dependent arteries would exhibit an enhanced KCl-mediated contractile response attributable to Ca²⁺ sensitization and increased Ca²⁺ channel current. Ameroid constrictors were surgically placed around the left circumflex (LCX) artery of female Yucatan miniature swine. Eight weeks postoperatively, pigs were randomized into sedentary or exercise-trained (treadmill run; 5 days/wk; 14 wk) groups. Small coronary arteries (150-300 μm luminal diameter) were isolated from myocardial regions distal to the collateral-dependent LCX and the nonoccluded left anterior descending arteries. Contractile tension and simultaneous measures of both tension and intracellular free Ca²⁺ levels (fura-2) were measured in response to increasing concentrations of KCl. In addition, whole cell Ca²⁺ currents were also obtained. Chronic occlusion enhanced contractile responses to KCl and increased Ca²⁺ sensitization in collateral-dependent compared with nonoccluded arteries of both sedentary and exercise-trained pigs. In contrast, smooth muscle cell Ca²⁺ channel current was not altered by occlusion or exercise training. Ca²⁺/calmodulin-dependent protein kinase II (CaMKII; inhibited by KN-93, 0.3-1 μM) contributed to the enhanced contractile response in collateral-dependent arteries of sedentary pigs, whereas both CaMKII and Rho-kinase (inhibited by hydroxyfasudil, 30 μM or Y27632, 10 μM) contributed to increased contraction in exercise-trained animals. Taken together, these data suggest that chronic occlusion leads to enhanced contractile responses to KCl in collateral-dependent coronary arteries via increased Ca²⁺ sensitization, a response that is further augmented with exercise training.NEW & NOTEWORTHY Small coronary arteries distal to chronic occlusion displayed enhanced contractile responses, which were further augmented after exercise training and attributable to enhanced calcium sensitization without alterations in calcium channel current. The calcium sensitization mediators Rho-kinase and CaMKII significantly contributed to enhanced contraction in collateral-dependent arteries of exercise-trained, but not sedentary, pigs. Exercise-enhanced contractile responses may increase resting arterial tone, creating an enhanced coronary flow reserve that is accessible during periods of increased metabolic demand.

Prostanoids counterbalance the synergism between endothelin-1 and angiotensin II in mesenteric veins of trained rats

Exercise-induced adaptations of the modulating mechanisms that influence the angiotensin (Ang II) responses assume different features depending on the venous bed. In femoral veins, exercise mobilizes vasodilator prostanoids to cooperate with NO in order to maintain reduced Ang II responses. On the other hand, exercise's influence on the Ang II responses in veins that drain blood from the mesenteric region has been poorly described. Therefore, the present study aimed to identify the effects of a single bout of exercise, as well as exercise training, on the Ang II responses in mesenteric veins. The present study also aimed to investigate the involvement of prostanoids, NO and ET-1 in eventual exercise-induced modifications in these veins. To this end, mesenteric veins taken from resting-sedentary, exercised-sedentary, resting-trained and exercised-trained animals were studied in organ baths. In addition, the mRNA expression of prepro-endothelin-1 (ppET-1), as well as that of the ET_A and ET_B receptors, were quantified by real-time PCR in these veins. The results show that, either in absence or in presence of L-NAME, the Ang II responses were not different between groups. In the presence of indomethacin, higher Ang II responses were observed in the resting-trained animals than in the resting-sedentary animals. This difference, however, disappeared when L-NAME, BQ-123 or BQ-788 were added during incubation. In addition, no differences in ppET-1, ET_A or ET_B mRNA expression were observed between groups. Furthermore, in the presence of PD123,319, the Ang II responses in the exercised-sedentary animals were higher than those in the resting-sedentary animals. In conclusion, exercise training mobilizes endothelin-1 (ET-1) to reinforce the Ang II-induced responses mainly through ET_A activation. On the other hand, vasodilator prostanoids are mobilized to act in parallel with NO in order to counterbalance the Ang II responses that have been potentiated by ET-1 in these trained animals.