Vascular responses of the spleen to rapid haemorrhage in the anaesthetized cat.

1. Splenic blood flow, splenic weight and arterial pressure were recorded in cats anaesthetized with sodium pentobarbitone. The mechanisms of the splenic contraction and vasoconstriction which followed rapid haemorrhage were investigated.2. When splenic arterial pressure was decreased progressively by mechanical occlusion of the coeliac artery, the decrease in splenic blood flow was proportional to the decrease in pressure; splenic weight did not change.3. After denervation of the spleen and adrenalectomy, haemorrhage resulted in a decrease in splenic flow which was similar to but slower than that in the innervated spleen; there was no splenic contraction. After splenic denervation, adrenalectomy and nephrectomy, haemorrhage caused a smaller decrease in flow but this response was still greater than that expected as a consequence of the reduced arterial pressure.4. Infusions of small doses of angiotensin caused splenic vasoconstriction with little change in splenic weight. Larger doses reduced both flow and weight.5. The splenic flow and weight responses to stimulation of the sympathetic nerves remained unimpaired when splenic blood flow was substantially reduced for 1-2 hr by haemorrhage.6. It is concluded that after a rapid haemorrhage, the splenic contraction is due only to activity of the splenic nerves and the adrenal medullae. The decrease in splenic flow is due to the reduction in arterial pressure, activity of the splenic nerves and the adrenal medullae, and the actions of angiotensin and some unidentified vasoconstrictor substance.