THE EFFECTS ON BLOOD-PRESSURE OF SECTION OF THE SPLANCHNIC NERVES

¹ Department of Physiology, Middlesex Hospital

1. The effects on blood-pressure of section of both splanchnic nerves have been studied in the cat under urethane, chloralose, ether, and amytal anæsthesia. In animals with the cardio-aortic and sinus nerves ("buffer" nerves) intact, a comparatively small fall of pressure results, commonly 0 to 15 per cent., and occasionally 25 per cent. This is the ease in spite of evident vasodilatation in the splanchnic area. Analysis shows that compensatory vasoconstriction probably occurs in other parts of the body, including the skeletal muscles. Evidence is given that the vasoconstrictor control of the vessels of skeletal muscle is of greater functional significance than is usually accepted.

2. When the buffer nerves are inactivated the extent of the fall is greater and exceeds on an average 50 per cent. It has been shown that this is not the result of the higher initial blood-pressure, and indicates (in agreement with Izquierdo and Koch) that the buffer nerves help to protect the circulation against a fall (as against a rise) of blood-pressure.

3. The fall of pressure is also diminished by the integrity of one pair of buffer nerves, and to a less extent by one intact sinus nerve. One intact cardio-aortic nerve alone is comparatively ineffective.

4. In the decerebrate preparation, even with the buffer nerves intact, splanchnic section produces an extensive fall of pressure.

5. The cardio-aortic nerves still display inhibitory tone after splanchnic section, even in the flayed animal, as shown by division of the vagi causing a rise of pressure even after atropine.

6. The rise of pressure resulting from occlusion of the carotids is diminished as a result of splanchnic section, even if the level of blood-pressure is unchanged.

7. Contrary to Moissejef, traction on the carotids lowers the pressure in an animal with vagi and splanchnics both divided.

The expenses of this research were partially defrayed out of a Government grant through the Royal Society.