Neurotransmission in isolated sheep mesenteric lymphatics

Area of Science:

• Physiology
• Pharmacology
• Vascular Biology

Background:

• Sheep mesenteric lymphatics exhibit spontaneous contractions.
• Understanding the neurochemical control of lymphatic contractility is crucial for lymphatic function.

Purpose of the Study:

• To investigate the neurotransmitters involved in the neural control of sheep mesenteric lymphatic contractions.
• To compare the neuropharmacology of sheep mesenteric lymphatics with other lymphatic tissues.

Main Methods:

• Isometric contractions of sheep mesenteric lymphatic rings were measured.
• Field stimulation was used to elicit contractions.
• Pharmacological agents including tetrodotoxin, alpha-antagonists (phentolamine, prazosin, yohimbine), noradrenaline, atropine, and alpha,beta-methylene ATP were employed.

Main Results:

• Field stimulation increased contraction frequency, blocked by tetrodotoxin, indicating a neural mechanism.
• Noradrenaline increased contraction frequency and force, which was blocked by phentolamine.
• Alpha-antagonists and atropine did not block the field stimulation response.
• Alpha,beta-methylene ATP induced a transient effect, and field stimulation response remained after desensitization.
• Combined noradrenaline and phentolamine blocked the field stimulation-induced increase in contraction frequency.

Conclusions:

• The neural control of sheep mesenteric lymphatics involves a transmitter distinct from noradrenaline acting on postsynaptic alpha-receptors.
• The neurotransmitter is unlikely to be ATP.
• The neuropharmacology of sheep mesenteric lymphatics is different from that of bovine mesenteric lymphatics.