Oxygen and cyclic nucleotides in human umbilical artery

Area of Science:

• Vascular smooth muscle physiology
• Cellular signaling pathways

Background:

• Oxygen (O2) exerts direct contractile effects on the human umbilical artery.
• Certain agonists induce contraction by increasing cyclic guanosine monophosphate (cGMP) without altering cyclic adenosine monophosphate (cAMP).
• These agonist effects involve both calcium (Ca++)-dependent and Ca++-inhibited mechanisms.

Purpose of the Study:

• To investigate the role of O2 and Ca++ in regulating cGMP synthesis in the human umbilical artery.
• To elucidate the distinct mechanisms controlling cGMP accumulation.

Main Methods:

• Measurement of cGMP and cAMP levels in response to various agents (agonists, ionophore, inhibitors).
• Assessment of O2 and Ca++ dependency of these responses.
• Utilizing inhibitors of oxidative phosphorylation and phosphodiesterase inhibitors.

Main Results:

• O2 increased cGMP in a Ca++-dependent manner, independent of oxidative phosphorylation.
• O2 was essential for Ca++-dependent cGMP accumulation induced by bradykinin, histamine, and A23187.
• Methylene blue and ascorbate induced cGMP accumulation independent of O2 and Ca++, but did not substitute for O2-dependent pathways.

Conclusions:

• The human umbilical artery possesses at least two distinct mechanisms for controlling cGMP synthesis.
• These pathways are differentially regulated by Ca++ and O2-linked processes.
• Understanding these mechanisms is key to comprehending vascular smooth muscle function.