Increased expression and activity of heme oxygenase-2 in pregnant rat aorta is not involved in attenuated vasopressin-induced contraction

Loss of Anticontractile Effect of Perivascular Adipose Tissue on Pregnant Rats: A Potential Role of Tumor Necrosis Factor-α

The present investigation examined the effect of pregnancy on the anticontractile effect of perivascular adipose tissue (PVAT) on the rat. Ring segments of the aorta, with and without PVAT, were set up in organ baths for isometric tension recording. In both groups, concentration-response curves to 5-hydroxytryptamine (5-HT) were displaced to the right with a reduction of the maximum response in aorta segments with PVAT. The anticontractile effect of PVAT was attenuated on segments from pregnant rats. 4-Aminopyridine (4-AP), an inhibitor of voltage-gated potassium (Kv) channels, enhanced 5-HT-induced contractions of aorta segments from pregnant and nonpregnant rats only when PVAT was attached. There was no difference in the effect of 4-aminopyridine on 5-HT-induced contractions of aorta segments with PVAT from pregnant and nonpregnant rats. There was also no significant difference in the expression of Kv7.4 channels in aorta segments (with PVAT) between pregnant and nonpregnant rats. Tumor necrosis factor-α (TNF-α) was detected in PVAT from pregnant and nonpregnant rats. The level of TNF-α was significantly greater in PVAT from pregnant rats. Treatment of pregnant rats with pentoxyphyline significantly reduced the level of TNF-α in the PVAT and restored the anticontractile effect of PVAT on aorta segments from pregnant rats. Finally, TNF-α (10 ng/mL) potentiated 5-HT-induced contractions of PVAT-containing pregnant rat aorta. These results would suggest that the loss of anticontractile effect of PVAT in pregnant rat aorta could be due to enhanced production of TNF-α in the PVAT in these rats.

Pregnancy-induced modulation of calcium mobilization and down-regulation of Rho-kinase expression contribute to attenuated vasopressin-induced contraction of the rat aorta

Normal pregnancy is characterized by attenuated vascular reactivity to a variety of contractile agonists and this, in part, has been attributed to increased circulating vasodilators and/or impaired Ca(2+)-influx through L-type Ca(2+)-channels. Our hypothesis in this study was that reduced Ca(2+)-dependent (influx) and Ca(2+)-independent (involving the RhoA/Rho-kinase pathway) mechanisms contributed to attenuated vasopressin-induced contraction of the pregnant rat aorta. AVP (10(-10) -3 x 10(-7) M) induced concentration-dependent contraction of aortic ring segments from nonpregnant and pregnant rats with no significant change in pD(2) values (8.53+/-0.11 and 8.33+/-0.18 in nonpregnant and pregnant rats, respectively). The maximum response was however significantly reduced in aorta segments from pregnant rats. Nifedipine (10(-6) M) significantly inhibited AVP-induced contraction in artery segments from nonpregnant but not pregnant rats indicating a reduced role for Ca(2+)-influx through L-type Ca(2+)-channels in AVP-induced contractions of the pregnant rat aorta. Western blot analysis revealed the expression of ROCK-1 and ROCK-II isoforms in aorta segments from both groups. There was a significant reduction in the expression of ROCK-1 and ROCK-II isoforms in aortic tissues from pregnant rats. This is consistent with the reduced potency of Y-27632 in inhibiting AVP (10(-7) M) induced contraction in aorta segments from pregnant rats. It was concluded that pregnancy-induced attenuated vascular response to AVP was due to decreased Ca(2+)-influx through L-type Ca(2+)-channels and decreased sensitization of the contractile myofilaments to Ca(2+).