Responses of sheep and kitten isolated coronary arteries to some vasoactive agents

In the present study, the effects of a range of vasoactive agents were assessed in sheep isolated coronary artery strips and in kitten isolated perfused coronary arteries. Both preparations contained muscarinic cholinoceptors. However, these receptors mediated contraction of sheep coronaries while dilatation was seen in the kitten. In sheep arteries, 5-hydroxytryptamine caused increases in resting tone and relaxation of acetylcholine-induced tone, while vasoconstriction was the predominant response in the kitten. Angiotensin increased tone in both preparations, although tachyphylaxis was evident. Conversely, adenosine and ATP caused reductions in tone in both preparations. Alpha-adrenoceptor agonists caused vasodilatation in kitten coronaries and decreased acetylcholine-induced tone in sheep arteries. However, weak contractions were observed in sheep coronaries in the absence of induced tone. Results also indicate that sympatomimetic amines mediate relaxation of sheep coronary arteries via beta 1-adrenoceptors. Sheep coronaries are readily and inexpensively obtained and provide a useful tool for the further study of coronary vascular smooth muscle.