A comparative study of adrenal medullary and cardiovascular responses to haemorrhage

• Main Author: Alabood, Abdulmuttalib Yousif Yakob
• Published: University of Edinburgh 1978
• Subjects: 612
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.640333

The release of catecholamine from the adrenal medulla during haemorrhage in the dog and rabbit, and its relationship to angiotensin formation has been studied. Catecholamine release was monitored using the superfused rat stomach strip. A superfused rat colon preparation was used to follow angiotensin generation. Controlled haemorrhage, lowering blood pressure to 50-60 mmHg were carried out in groups of animals before and after cholinergic muscarinic blockade with hyoscine methyl bromide. In rabbits, catecholamine release increased towards the end of the bleed. It was not continuous and decreased soon after haemorrhage stopped. It was not reduced by muscarinic blockade but was abolished by nicotinic blockade. Heart rate did not increase significantly in this species during haemorrhage and fell below control levels 30 minutes after haemorrhage. No evidence of increased angiotensin generation during or after haemorrhage was noted. Angiotensin infusions gave no indication of causing catecholamine release. In dogs, catecholamine release commenced as the blood pressure began to fall. The release was continuous over the whole period of hypotension. It returned to normal when retransfusion of shed blood was carried out. Heart rate increased during haemorrhage but returned to control level within 30 minutes after bleed. Muscarinic blockade had no effect on catecholamine release. Hexamethonium, however, reduced but did not entirely prevent release during haemorrhage. Moreover, catecholamine output was transient persisting for only a few minutes. Ligation of the renal veins after hexamethonium totally abolished catecholamine release during haemorrhage. Angiotensin levels increased markedly after haemorrhage. Infusions of angiotensin significantly increased the release of catecholamine in transient bursts persisting for only 2-3 minutes. The species differences noted are discussed in the context of cardiovascular control in hypotensive states.