Contractile responses to vasoconstrictor agents were compared in helical strips of dog and monkey epicardial coronary arteries of different sizes. Contractions of large, medium and small arteries induced by KCl ( 30mM ) were virtually identical. Contractions induced by 5-hydroxytryptamine (5-HT) (10(-9) - 2 X 10(-6) M) were in the order of large greater than medium greater than small arteries in dogs, and large = medium greater than small arteries in monkeys. Cinanserin suppressed these responses. In contrast, contractions produced by angiotensin II (AII) (10(-7) M) were in the order of small greater than medium greater than large arteries in dogs, and small greater than medium = large arteries in monkeys. Sar1-Ala8-angiotensin II markedly attenuated the peptide-induced contractions. Contractions induced by prostaglandin F2 alpha (PGF2 alpha) were significantly greater in large and medium sized arteries than in small arteries in dogs, while those of the arteries of different sizes isolated from monkeys did not differ. Contractions induced by carbocyclic thromboxane A2 (c-TXA2), in arteries of different sizes in dogs and monkeys, did not differ. These results suggest that the sensitivity and/or the population of 5-HT receptors are greater in proximal coronary arteries than in distal arteries, while, in contrast, the sensitivity and/or population of AII receptors are greater in distal coronary arteries. Receptors for PGF2 alpha and c-TXA2 appear to react to a similar degree in monkey arteries of different sizes, although receptors for PGF2 alpha appear to be fewer in distal coronary arteries in dogs.