1. An ‘isogravimetric’ technique, plus measurement of pressure in a small artery, was used to investigate the responses of upstream and downstream precapillary and postcapillary resistance vessels in the hindquarters of spontaneously hypertensive rats (SHR) and normal control rats perfused at constant flow.
2. Dose—response curves to noradrenaline were constructed under conditions of low or normal calcium.
3. In both control rats and SHR the dependence on external calcium during contraction increased peripherally, with the smaller pre- and post-capillary resistance vessels being most dependent and larger arteries least dependent.
4. There may be differences between SHR and control rats in regard to the handling of calcium, particularly in the small pre- and post-capillary resistance vessels.