Reflex respiratory and cardiovascular effects of stimulation of receptors in the nose of the dog.

1. In forty-one out of forty-seven dogs under chloralose-urethane or Nembutal anaesthesia, mechanical stimulation of the nasal mucous membrane caused a reduction or inhibition of respiration, bradycardia, variable changes of arterial blood pressure, and a small rise in venous pressure.2. Simultaneous measurements of arterial and venous pressures, and also of blood flow in various arteries by means of an electromagnetic flowmeter indicate that the calculated vascular resistance increases in the intact limb, muscle, and skin, and the vascular beds of the vertebral, superior mesenteric, renal and splenic arteries. No changes in vascular resistance occur in the common carotid circulation.3. Evidence is presented that the increase in vascular resistance is due to vasoconstriction, and occurs in the absence of changes in pulmonary ventilation.4. Stimulation of the nasal mucous membrane causes a reduction in volume of the spleen.5. The respiratory and cardiovascular responses are reflex in nature, being abolished by the application of a local anaesthetic to the nose or by combined division of the maxillary and ethmoidal branches of the trigeminal nerves. The cardiac response is mediated largely by the vagus nerves, and the vascular responses by sympathetic adrenergic fibres.6. Cessation of the stimulus to the nose not infrequently results in the following temporary after-effects: hyperventilation, tachycardia, hypertension, and vasodilatation in the intact limb and in muscle.