Is adrenaline released by sympathetic nerves in man?

Prior research has shown that adrenaline is primarily secreted by the adrenal medulla. However, the role of sympathetic nerve endings in adrenaline release remains unclear. This gap motivated a study to investigate whether adrenaline can be released from non-adrenal sources in humans. It was already known that noradrenaline is released by sympathetic nerves, but the contribution of adrenaline is uncertain. No prior work had resolved whether adrenaline functions as a cotransmitter in sympathetic nerve terminals. This uncertainty is especially relevant in conditions like hypertension and heart failure. The study aimed to address this by measuring regional adrenaline release in specific organs. These measurements could clarify the physiological and pathological roles of adrenaline beyond adrenal secretion.

The study aimed to determine if adrenaline is released from sympathetic nerve endings in humans. This was done to test a theory about essential hypertension that suggests adrenaline may act as a cotransmitter. The researchers focused on measuring adrenaline release in the heart, lungs, and liver. They also examined adrenaline release in the renal vein and during physical and mental stress. The goal was to distinguish between adrenal and non-adrenal sources of adrenaline. The study sought to clarify whether adrenaline is released in response to sympathetic activation. This could help explain how adrenaline might influence cardiovascular responses. The findings could provide insights into the mechanisms of hypertension and heart failure.

The researchers used radiotracer methods to measure adrenaline and noradrenaline release in specific regions of the body. These methods allowed them to track the release of these catecholamines into plasma. They focused on the heart, lungs, liver, and kidneys in healthy individuals. The study also included patients with heart failure and phaeochromocytoma. Mental challenge and isometric exercise were used to activate sympathetic nerves. Supine bicycle exercise was employed to increase sympathetic outflow. Adrenaline release was measured in the right renal vein and compared to other regions. The radiotracer data provided quantitative estimates of adrenaline release rates.

In healthy resting individuals, no adrenaline release was detected from the heart, lungs, or liver. Adrenaline was found in the right renal vein, but the source was likely the adrenal medulla. During mental stress and isometric exercise, cardiac adrenaline release remained undetectable. Supine bicycle exercise increased noradrenaline release 10-30 fold, but adrenaline release averaged only 2.36 ng/min. In patients with heart failure, adrenaline release was clearly detectable from non-adrenal sources. Those with phaeochromocytoma also showed regional adrenaline release at rest. These findings suggest that adrenaline can be released from sympathetic nerves in certain conditions. However, the functional significance of this release remains to be fully determined.

The study found that adrenaline is released from non-adrenal sources in humans, particularly during exercise and in certain disease states. This release likely occurs from sympathetic nerve endings rather than the adrenal glands. In healthy individuals at rest, no adrenaline release was observed from the heart, lungs, or liver. Adrenaline was detected in the renal vein, but the source was suspected to be adrenal. During exercise, adrenaline release remained low compared to noradrenaline. In patients with heart failure and phaeochromocytoma, adrenaline release was clearly evident. The authors suggest that this release could influence cardiovascular responses. Whether this release contributes to hypertension remains to be tested.