On the neurogenic vasoconstriction of the resistive vessels in cutaneous vascular bed--rabbit ear

A study was made of the effect of increased sympathetic activity during bilateral carotid occlusion (BCO), during haemorrhage and during i.v. injection of Tetramethylammonium jodatum (TMAI) on the resistive vessels in rabbit ears. The animal was under slight urethane anaesthesia, with spontaneous respiration after tracheotomy and vagotomy. The ear was perfused by roller pump with constant flow with tempered oxygenized Tyrode solution or with blood from a donor-animal. The increase in sympathetic activity during BCO, haemorrhage and injection of 100 mg/kg TMAI did not change the perfusion pressure in the perfused rabbit ear. The initial perfusion of the ear with blood increased the resistance of the ear, while perfusion with blood from donor-animal which had suffered considerable haemorrhage caused additional increase in the resistance by about 150 per cent. The effect of sympathetic constrictory influence of the resistive vessels is studied in view of the anatomic-functional specificities of the nerve supply of the ear and of the cutaneous vessels, in view of the passive dilatation of the resistive vessels, and of the thermoregulatory function of the ear. It is indicated that considerable hormonal vasoconstriction probably occurs in the rabbit ear during haemorrhage.