Endocrine Abstracts

Objectives: Adenosine is a purinergic mediator involved in the regulation of many physiological and pathological processes. It acts as neurotransmitter in the central and autonomic nervous system, where it counterbalanaces sympathetic activity. Adenosine is produced by majority of human cellsexerting autocrine, paracrine as well as systemic effects. Due toits vasodilatatory and negative inotropic effects it seems to play a role in ethiopathogenesis of orthostatic intolerance, particularly in vasovagal syncope.

Aim: Of this pilot study was to compare baseline (before head up tilt test - HUTT) and stimulated (after HUTT) serum levels of adenosine between patients with positive and negative HUTT and to compare serum levels of adenosinedeaminase (ADA) between positive and negative patients.

Subjects and methods: Group of 39 patients with history of at least one syncope or presyncope underwent HUTT. According to the response during the test, they were divided into HUTT positive (n=29, age 31.38+4.9) and HUTT negative (n=10, age 39.85+2.7). HUTT was performed according to Italian protocol, with continual ECG monitoring and BP measurement. Blood sampling was realized before and immediately after HUTT. Serum adenosine and ADA levels were evaluated by ELISA method.

Results: HUTT positive patients had significantly higher levels of baseline adenosine than those with HUTT negativity (3.17 vs 1.78 ng/ml; P=0.03). There was no significant difference in adenosine levels after HUTT, between HUTT positive and HUTT negative patients, but HUTT positive patients tended to have higher stimulated levels of adenosine (3.59 vs 1.87 ng/ml; P=0.08). Serum ADA activity was similar in both groups (10.9 vs 9.6 IU/l; P=0.83).

Conclusion: HUTT positive patients had significantly higher serum adenosine as compared to those HUTT negative. We conclude that adenosine may play a role in the etiopathogenesis of vasovagal syncope and states with orthostatic intolerance.