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Plasticity of adenosine and endothelin I tone on cardiovascular function in embryonic chickens (Gallus domesticus): effects of developmental hypoxia (879.5)

Chronic hypoxic incubation of embryonic chickens is a common environmental challenge used to assess plasticity in the development of cardiovascular function in vertebrates. Hypoxic stress increases vascular growth, circulating catecholamines, and cholinergic tone while decreasing resting arterial pressure, adrenergic tone, and sensitivity to exogenous nitric oxide in some chicken breeds. Given the limited contribution of the central nervous system to cardiovascular homeostasis throughout the majority of chicken development hypoxia may also alter regulatory elements if they exhibit plasticity. We investigated the plasticity of key local regulatory ligands, adenosine and endothelin I in embryonic chickens induced by hypoxia (15%O2). At day 15 (70%) and 19 (90%) of a 21 day incubation period embryos from normoxic and hypoxic conditions were instrumented to measure arterial pressure and heart rate. Adenosine produced a dose dependent hypotensive bradycardia that increased in intensity with age. Endothelin I produced a pronounced hypertension at the maximal dose on day 15 and a dose dependent hypertension at day 19. Chronic hypoxic incubation blunted the adenosine response while it intensified the pressure response to endothelin I. Finally, the embryonic cardiovascular response adenosine receptor blockade with theophylline on day 19, a sustained hypertension, was absent in embryos incubated in 15% O2. These findings indicate embryonic chickens utilize adenosine and endothelin I to maintain cardiovascular homeostasis. Further both responses exhibit regulatory factor specific plasticity.