Fig. 8. The effect of L-NAME on mean external contraction ratios. In this experiment, one demibranch was exposed to L-NAME for 15 min prior to exposure to 2x10^-5 mol l^-1 5HT, while the control demibranch was only exposed to 2x10^-5 mol l^-1 5HT. The open circle represents data collected in August, when potentiation is absent. Values are means ± 1 S.E.M., N=3-10.