The relationship between vessel size and the magnitude of pulmonary vasomotor responses (% change in vessel internal diameter) in (a) Dahl salt-sensitive rats (Dahl-S; n = 7), (b) Dahl salt-resistant rats (Dahl-R; n = 7) and, for comparative purposes, (c) SD rats [§taken from Schwenke et al. (2011)] in response to the i.v. administration of sodium nitroprusside (SNP, 5.0 µg kg−1 min−1 for 5 min; closed circles) and ACh (3.0 µg kg−1 min−1 for 5 min; open circles). (d) Magnitude of vasomotor response of all groups of rats in response to ET-1A receptor blockade (BQ-123, 1 mg kg−1). *Significant reduction/increase in vessel caliber (P < 0.05). †Significant difference in the magnitude of response to ACh versus SNP (P < 0.05). ‡Significant difference between Dahl-R and Dahl-S rats (P < 0.05).