Nitroxidergic nerve stimulation relaxes human uterine vein

Area of Science:

• Pharmacology
• Neuroscience
• Reproductive Biology

Background:

• Nitroglycerin, a nitric oxide (NO) donor, predominantly affects veins over arterioles.
• The role of endogenous NO from vasodilator nerves in regulating human uterine venous tone is not well understood.

Purpose of the Study:

• To investigate whether endogenous NO released from vasodilator nerves regulates the tone of human uterine venous strips.
• To identify the neurotransmitter responsible for vasodilation in human uterine veins.

Main Methods:

• Isolated human uterine venous strips were used.
• Vascular responses to nicotine were assessed in the presence of various antagonists, including prazosin (alpha 1-adrenoceptor antagonist), timolol, atropine, and indomethacin.
• The effects of oxyhemoglobin and NG-nitro-L-arginine (L-NA), a NO synthase inhibitor, on nicotine-induced relaxations were evaluated.
• Nitric oxide (NO)-induced relaxation was also studied in the presence of L-NA and oxyhemoglobin.

Main Results:

• Nicotine induced contractions or relaxations in partially contracted human uterine veins.
• Prazosin reversed nicotine-induced contractions to relaxations.
• Nicotine-induced relaxations in prazosin-treated strips were abolished by oxyhemoglobin and L-NA, but not by timolol, atropine, or indomethacin.
• L-NA's inhibitory effect was reversed by L-arginine, and its enantiomer D-NA was ineffective.
• NO-induced relaxation was unaffected by L-NA but abolished by oxyhemoglobin.

Conclusions:

• Human uterine veins are innervated by vasodilator nerves that liberate nitric oxide (NO) as a vasodilator neurotransmitter.
• Norepinephrine from adrenergic nerves contracts venous smooth muscle via alpha 1-adrenoceptor stimulation.