Ligamentum arteriosum: Muscular and contractile

Area of Science:

• Cardiovascular Anatomy and Physiology
• Fetal Circulation
• Histology and Cell Biology

Background:

• The ductus arteriosus is a crucial fetal vessel shunting blood past the lungs.
• Postnatally, it becomes the ligamentum arteriosum (LA), typically considered a fibrosed remnant.
• Conflicting reports suggest the LA may retain muscular characteristics.

Purpose of the Study:

• To investigate the hypothesis that the ligamentum arteriosum retains contractile muscular elements.
• To determine the cellular composition and functional properties of the LA in mammals.

Main Methods:

• Histological staining (routine and special) of mouse, pig, and human LA.
• Single-immunolabeling for α-smooth muscle actin.
• Transmission electron microscopy (mouse and pig).
• Organ bath tension recording of explanted pig LA with pharmacological stimulation.

Main Results:

• The LA in all three species was predominantly composed of α-smooth muscle actin-positive cells.
• LA myocytes demonstrated contraction in response to noradrenalin (NA).
• NA-induced contractions were relaxed by α1-adrenergic blockers (prazosin, tamsulosin).

Conclusions:

• The ligamentum arteriosum is not a passive fibrosed remnant but a muscular and contractile structure.
• Contractile LA myocytes may influence the distensibility of the aorta and pulmonary artery.
• This challenges the established understanding of the ligamentum arteriosum's post-natal role.