Role of Extracellular Calcium and Calcium Sensitization in the Anti-Contractile Effect of Perivascular Adipose Tissue in Pregnant Rat Aorta

Previous studies have shown that the anti-contractile effect of the perivascular adipose tissue (PVAT) is attenuated in pregnancy. In the present investigation, we have examined the possibility that this loss of anti-contractile effect could be due to changes in calcium mobilization. PVAT exerted anti-contractile effect against 5-hydroxytryptamine (5-HT)-induced contractions of aorta segments from pregnant and non-pregnant rats and this anti-contractile effect was attenuated in segments from pregnant rats. Nifedipine (10^–6 mol/L), an inhibitor of L-type dihydropyridine calcium channels, significantly reduced 5-HT-induced contraction of aorta segments from non-pregnant and pregnant rats with and without PVAT. The inhibitory effect of nifedipine against 5-HT-induced contractions was attenuated in PVAT-free aorta segments from pregnant rats. However, while PVAT reduced the effectiveness of nifedipine in aorta segments from non-pregnant rats, it partially restored the inhibitory effect of nifedipine in aorta segments from pregnant rats. Inhibitors of calcium sensitization, Y-27632 (10^–6 mol/L) and GF 109203X (10^–6 mol/L), significantly reduced 5-HT-induced contractions of PVAT-free aorta segments from non-pregnant and pregnant rats. Both inhibitors, however, were less effective in aorta segments from pregnant rats. The presence of PVAT reduced the effectiveness of Y-27632 and GF 109203X in aorta segments from pregnant and non-pregnant rats. Protein expression of Rho-associated protein kinase (ROCK) I and II was detected in aorta segments and PVAT from pregnant and non-pregnant rats. There was a reduction in the expression of both isoforms in aorta segments but not PVAT from pregnant rats. In addition, there was no significant difference in the expression of ROCK-I and ROCK-II in PVAT from pregnant and non-pregnant rats. We concluded that the loss of anti-contractile effect of PVAT in aorta segments from pregnant rats could be due to increased influx of extracellular calcium through nifedipine-sensitive dihydropyridine channels.