Table 2

Effects of receptor antagonists on RB-induced increase in contraction amplitude

Antagonist^2-a	RB^2-b Alone	RB + Antagonist
Phentolamine	2.16 ± 0.13	2.17 ± 0.15
dl-Propranolol	2.20 ± 0.18	2.15 ± 0.13
Pyrilamine	2.02 ± 0.07	2.09 ± 0.07
Cimetidine	2.21 ± 0.18	2.32 ± 0.24

Papillary muscles were stimulated at 2 Hz and exposed to the agents. Contraction amplitudes represent relative values to those obtained immediately before application of the agents. Values are mean ± S.E. (n = 4).

↵2-a Concentration of the antagonists was 5 μM.
↵2-b Concentration of RB was 20 μM.