Vascular perfusion limits mesenteric lymph flow during anaphylactic hypotension in rats

Area of Science:

• Physiology
• Immunology
• Vascular Biology

Background:

• Anaphylaxis causes systemic hypotension and increased vascular permeability.
• Splanchnic vascular bed fluid extravasation is a key factor in anaphylactic shock.
• Mesenteric lymph flow (Q(lym)) is a direct indicator of fluid movement in the splanchnic circulation.

Purpose of the Study:

• To investigate fluid extravasation in the splanchnic vascular bed during anaphylactic hypotension.
• To determine the role of portal venous pressure (P(pv)) in antigen-induced increases in mesenteric lymph flow (Q(lym)).
• To assess the impact of altered splanchnic vascular surface area on fluid dynamics during anaphylaxis.

Main Methods:

• Anesthetized rats sensitized with ovalbumin were used to model anaphylaxis.
• Systemic arterial pressure (P(sa)), portal venous pressure (P(pv)), and mesenteric lymph flow (Q(lym)) were continuously monitored.
• Portal venous pressure was mechanically elevated in control rats to isolate its effect on Q(lym).
• Mesenteric arterial flow was measured to assess changes in splanchnic vascular surface area.

Main Results:

• Antigen injection caused a sharp decrease in P(sa) and a transient increase in P(pv) and Q(lym) in sensitized rats.
• Mechanically elevating P(pv) alone in nonsensitized rats mimicked the increase in Q(lym) observed in anaphylaxis.
• Lymph protein concentrations increased, confirming enhanced vascular permeability.
• Mesenteric arterial flow decreased significantly more in sensitized rats (75%) compared to controls (50%), indicating reduced vascular surface area.

Conclusions:

• Anaphylaxis-induced mesenteric lymph flow increase is primarily driven by elevated capillary pressure due to increased P(pv).
• Increased vascular permeability contributes to fluid extravasation.
• Reduced splanchnic vascular surface area and filtration pressure subsequently limit the extent of fluid extravasation.