Effects of histamine and acetylcholine on equine digital lymph flow and composition.

This study explored the effects of histamine and acetylcholine on the flow and composition of lymph in the legs of horses. The researchers found that while acetylcholine did not significantly alter lymph flow or protein concentration, histamine infusion led to an increase in both measurements and the development of edema.

Methodology

• The researchers collected lymph from a lymphatic node in the digit (a part of the limb) of eight anesthetized ponies.
• They assessed the flow rate (how quickly the lymph moves), protein concentration (the amount of protein in the lymph), systemic arterial pressure (blood pressure in the body’s major artery), and small vein pressure (pressure within small blood vessels).

Control Measurements and Infusion Experiments

• In a normal (control) state, lymph flow averaged 0.068 ml/min, featuring 3.11 g/100 ml of protein with a ratio of 0.75 between two types of proteins (albumin and globulin).
• The scientists then manipulated conditions by introducing two chemicals locally into the ponies’ arteries – acetylcholine for twenty minutes, and subsequently histamine for 60 minutes.

Observations Pertaining to Acetylcholine Infusion

• The infusion of acetylcholine led to elevated small vein pressure, but did not change the lymph flow rate or protein concentration.

Observations Pertaining to Histamine Infusion

• Infusion of histamine caused a significant and lasting increase in small vein pressure as well as in the lymph flow rate and protein concentration.
• The area receiving histamine also developed edema (excess fluid trapped in the body’s tissues).

Conclusions

• The researchers concluded that in horses, similar to other species, histamine-induced edema, is due to a reduction in the pressure gradient responsible for protein (colloid) movement across capillaries, rather than an increase in the pressure pushing fluid out of them (hydrostatic pressure gradient).

This research contributes to understanding how different chemicals can affect the lymphatic system and could inform future studies or treatments related to circulation, edema, or conditions affecting the lymphatic system.