Korean J Physiol Pharmacol.  2022 Jul;26(4):255-262. 10.4196/kjpp.2022.26.4.255.

Oxytocin-induced endothelial nitric oxide dependent vasorelaxation and ERK1/2-mediated vasoconstriction in the rat aorta

• Xu Q
• Zhuo K
• Zhang X
• Zhang Y
• Xue J
• Zhou MS

• KMID: 2530945
• DOI: http://doi.org/10.4196/kjpp.2022.26.4.255

Abstract

Oxytocin is a neuropeptide produced primarily in the hypothalamus and plays an important role in the regulation of mammalian birth and lactation. It has been shown that oxytocin has important cardiovascular protective effects. Here we investigated the effects of oxytocin on vascular reactivity and underlying the mechanisms in human umbilical vein endothelial cells (HUVECs) in vitro and in rat aorta ex vivo. Oxytocin increased phospho-eNOS (Ser 1177) and phospho-Akt (Ser 473) expression in HUVECs in vitro and the aorta of rat ex vivo. Wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K), inhibited oxytocin-induced Akt and eNOS phosphorylation. In the rat aortic rings, oxytocin induced a biphasic vascular reactivity: oxytocin at low dose (10^-9–10-8 M) initiated a vasorelaxation followed by a vasoconstriction at high dose (10^-7 M). L-NAME (a nitric oxide synthase inhibitor), endothelium removal or wortmannin abolished oxytocin-induced vasorelaxation, and slightly enhanced oxytocin-induced vasoconstriction. Atosiban, an oxytocin/ vasopressin 1a receptor inhibitor, totally blocked oxytocin-induced relaxation and vasoconstriction. PD98059 (ERK1/2 inhibitor) partially inhibited oxytocin-induced vasoconstriction. Oxytocin also increased aortic phospho-ERK1/2 expression, which was reduced by either atosiban or PD98059, suggesting that oxytocin-induced vasoconstriction was partially mediated by oxytocin/V1aR activation of ERK1/2. The present study demonstrates that oxytocin can activate different signaling pathways to cause vasorelaxation or vasoconstriction. Oxytocin stimulation of PI3K/eNOS-derived nitric oxide may participate in maintenance of cardiovascular homeostasis, and different vascular reactivities to low or high dose of oxytocin suggest that oxytocin may have different regulatory effects on vascular tone under physiological or pathophysiological conditions.

Keyword

Endothelial nitric oxide synthase; Oxytocin; Phosphatidylinositol 3-kinase; Vascular reactivity

Figure

• 

  Fig. 1 Effects of oxytocin on the protein expressions of phospho-endothelial nitric oxide synthesis (peNOS, Ser 1177) and eNOS in HUVECs. Oxytocin time-dependently increased peNOS (A) but not total eNOS expression (B), oxytocin dose-dependently increased peNOS (C) but not total eNOS expression (D). Data is expressed as mean ± SE. n = 6. HUVECs, human umbilical vein endothelial cells; OT, oxytocin. *p < 0.05 vs. control group.

• 

  Fig. 2 Effects of PI3K inhibitor wortmannin or oxytocin/vasopressin 1a receptor antagonist atosiban on pAkt (tyr473) or peNOS (ser1177) in the cultured HUVECs. Oxytocin dose-dependently increased Akt phosphorylation (A); Either wortmannin or atosiban significantly attenuated oxytocin-induced Akt (B) or eNOS phosphorylation (C). PI3K, phosphatidylinositol 3-kinase; HUVECs, human umbilical vein endothelial cells; OT, oxytocin; Wort, wortmannin; Ato, atosiban. n = 6, *p < 0.05 vs. control group, #p < 0.05 vs. oxytocin group.

• 

  Fig. 3 Effects of oxytocin on pAkt (Tyr 473) and peNOS (Ser 1177) expressions in the rat aorta ex vivo. Incubation of oxytocin (10 nM) for 5 min ex vivo significantly increased pAkt (Tyr 473, A) and peNOS (Ser 1177, B) expression. Either wortmannin or atosiban prevented oxytocin-indued pAkt (C) and peNOS (D) expression. OT, oxytocin; Wort, wortmannin; Ato, atosiban. n = 8, *p < 0.05 vs. control group; #p < 0.05 vs. oxytocin group.

• 

  Fig. 4 Effect of oxytocin (OT) on the vascular reactivity in the rat’s aortic rings pre-constricted by norepinephrine. (A) L-NAME (an inhibitor of nitric oxide synthase) or endothelium removal (EC–) abolished oxytocin-induced vasorelaxation and slightly enhanced oxytocin-induced vasoconstriction; (B) Atosiban or wortmannin abolished oxytocin-induced vasorelaxation. n = 8. *p < 0.05 vs. oxytocin group.

• 

  Fig. 5 Oxytocin induced vasoconstriction in the unstimulated rat’s aortic rings. L-NAME (an inhibitor of nitric oxide synthase) (A) or endothelium removal (B) slightly enhanced oxytocin-induced vasoconstriction; (C) SQ29548 (an inhibitor of prostaglandin H2/thromboxane A2) did not affect oxytocin-induced vasoconstriction; (D) Atosiban completely abolished oxytocin-induced vasoconstriction; (E) PD98059 (an inhibitor of ERK1/2 activation) partially inhibited oxytocin-induced vasoconstriction; (F) Effect of oxytocin on phospho-ERK1/2 expression. OT, oxytocin; Ato, atosiban. n = 8. *p < 0.05 vs. control group, #p < 0.05 vs. oxytocin group.

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