The vascular responses of the spleen to intravenous infusions of catecholamines, angiotensin and vasopressi in the anaesthetized cat.

1. Splenic arterial flow and splenic weight were recorded in cats anaesthetized with sodium pentobarbitone. The responses of the spleen to catecholamines, angiotensin and vasopressin were investigated.2. Catecholamines caused responses mediated by alpha- and beta-adrenoceptors in the arteriolar smooth muscle, but only insignificant beta-adrenoceptor responses could be elicited from the capsular smooth muscle. The difficulties in elucidating the mechanism of action of catecholamines on arteriolar smooth muscle are discussed.3. Angiotensin caused marked vasoconstriction, but contraction of the capsular smooth muscle was less marked. Vasopressin caused vasoconstriction but had no effect on capsular smooth muscle. Thus these peptides constrict the resistance vessels but produce much weaker contraction of the capsule.4. These responses are discussed in relation to the splenic responses to acute haemorrhage.