Dopamine-sensitive receptors that evoke rumination and modify reticulo-ruminal activity in sheep

Area of Science:

• Veterinary Neuroscience
• Gastrointestinal Physiology

Background:

• Dopamine's role in ruminative behavior and gastrointestinal motility is complex.
• Understanding dopamine's receptor interactions is crucial for managing digestive functions in livestock.

Purpose of the Study:

• To investigate the specific mechanisms and receptor subtypes involved in dopamine-induced rumination and modulation of reticular contractions in sheep.
• To differentiate between central and peripheral effects of dopamine on digestive processes.

Main Methods:

• Dopamine was administered via bolus injection or infusion into the carotid artery, coeliac artery, or left gastric artery in sheep.
• Pharmacological agents including alpha-adrenoreceptor antagonists (phentolamine, yohimbine) and a dopaminergic antagonist (metoclopramide) were used to probe receptor involvement.
• Reticular contractions and rumination were monitored to assess dopamine's effects.

Main Results:

• Dopamine bolus injections into the coeliac or left gastric arteries evoked rumination, blocked by alpha-antagonists but not metoclopramide, suggesting peripheral alpha 2-adrenoreceptor activation.
• Dopamine infusion into the carotid artery reduced reticular contraction frequency via a central dopaminergic mechanism.
• Dopamine infusion into peripheral arteries reduced reticular contraction amplitude via a peripheral mechanism sensitive to both metoclopramide and phentolamine.

Conclusions:

• Dopamine stimulates rumination primarily through peripheral alpha 2-adrenoreceptors in the gastric region.
• Dopamine modulates reticular contractions via distinct central (dopaminergic) and peripheral (metoclopramide/phentolamine-sensitive) mechanisms.
• The route of dopamine administration significantly influences its effects on sheep digestive physiology.