In rabbits under pentobarbitone anaesthesia stimulation of the nasal mucous membrane with ether vapour causes apnoea, bradycardia and a rise in arterial blood pressure. 2. Simultaneous measurements of femoral arterial blood pressure and of femoral arterial or venous blood flow show that vascular resistance increases in both the intact and skinned hind limb in response to nasal stimulation. Evidence is presented to show that the increase in hind-limb vascular resistance is due to vasoconstriction which is relfex in nature. 3. The change in vascular resistance in the hind limb following nasal stimulation may be divided into two distinct phases. The primary (early) phase is mediated by the efferent sympathetic nerves to the limb whereas the secondary (late) phase is mediated by adrenal gland hormones. 4. The secondary phase of the hind-limb vascular response is invariably less pronounced than the primary phase, and with regard to the time course of the appearance of the two phases of the response it appears that following stimulation of the nose there is no mutual reinforcement of sympathetic neural and humoral influences on the hind-limb blood vessels. 5. The cardiovascular response occur in the absence of changes in pulmonary ventilation.
