The Effects of Vasoconstrictor Fibre Stimulation on the Consecutive Vascular Sections of the Small Intestine of the Cat during Prolonged Regional Hypotension

A plethysmographic technique was used on the cat to investigate the effects of electrical stimulation of the regional sympathetic vasoconstrictor fibres on intestinal consecutive vascular sections during prolonged hypotension at approximately 55 or 30 mm Hg produced by graded arterial occlusion. The initial peak resistance and the capacitance responses declined continuously throughout the hypotensive period, the rate of decline being higher the lower the per‐fusion pressure. After 2.5 h hypotension at 30 mm Hg the nervous vasoconstrictor effects on the resistance and capacitance vessels amounted to 50 and 30 per cent of control, respectively. The reactivity of the precapillary sphincters as reflected in the capillary filtration coefficient (CFC), was largely unaltered during the hypotension at the 55 mm Hg level. At the lower perfusion pressure a marked increase of CFC was noted between and during nervous stimulations. Mean capillary hydrostatic pressure was not significantly changed by nervous activation, hut seemed to increase in the latter half of most experiments at 30 mm Hg. When releasing the arterial clamp after a 30 mm Hg hypotension the whole cardiovascular system seemed to derange progressively. Mucosal ulcerations and bleedings were regularly found in all these animals.