Local regulators of hepatic sinusoidal microcirculation: recent advances

Area of Science:

• Hepatology
• Vascular Biology
• Microcirculation Physiology

Background:

• Hepatic microcirculation is crucial for liver function.
• Local regulatory mechanisms of sinusoidal blood flow are complex.
• Endothelin (ET)-1 is a potent vasoconstrictor influencing liver hemodynamics.

Purpose of the Study:

• To review recent studies on the local regulation of hepatic microcirculation.
• To investigate the roles of sinusoidal endothelial cells and inlet sphincter-like structures.
• To elucidate the mechanism of dynamic changes in sinusoidal endothelial fenestrae (SEF) and vascular structures induced by ET-1.

Main Methods:

• Enzymohistochemical demonstration of arterial capillaries.
• Intravital microscopy of hepatic microcirculation.
• Review of studies on endothelin (ET)-1 and nitric oxide (NO) mediated regulation.

Main Results:

• Identified two types of sphincter-like structures at sinusoid entry points.
• Demonstrated direct termination of terminal hepatic arterioles into sinusoids.
• Showed that ET-1 induces dynamic changes in SEF, terminal portal venules, and terminal hepatic arterioles.
• Highlighted the coordinated role of sphincter-like structures, SEF, and hepatic stellate cells (HSCs) in blood flow control.
• Indicated that sinusoidal endothelium-derived ETs and NO mediate these changes.
• Confirmed the intracellular Ca++-calmodulin-actomyosin system underlies SEF and HSC contractility.

Conclusions:

• Hepatic microcirculation is locally regulated by sphincter-like structures and SEF dynamics.
• Sinusoidal endothelial cells play a key role in mediating vascular tone via ETs and NO.
• The coordinated action of these elements ensures precise control of hepatic sinusoidal blood flow.