Inhibition of rumination in sheep by alpha-adrenoreceptor antagonists

Rumination activity was recorded in sheep during a period of 3 h. The amount of rumination occurring in 30 min following the intravenous injection of an alpha 1 blocking drug (prazosin, 0.1 mg/kg) and an alpha 2 blocking drug (idazoxan, 0.1 mg/kg) was reduced compared with control days when saline was given. The observation that rumination can be stimulated by a rapid, intravenous dose of adrenalin was confirmed. The induction of rumination by adrenalin was prevented by these alpha-adrenoreceptor antagonists given singly or together at the dose rate mentioned. These findings are discussed in the light of knowledge that normal reticulo-ruminal motility and food intake can be inhibited by stimulation of alpha 2-adrenoreceptors.