Catecholamines in the sympathetic nervous system of the domestic fowl

In order to resolve some existing uncertainties regarding the identity of the sympathetic catecholamine neurotransmitter in birds, we have measured endogenous noradrenaline (NA), adrenaline (AD) and dopamine (DA) in various peripheral tissues and in the paravertebral sympathetic chain of the domestic fowl. In all visceral tissues examined - atrium, spleen, mesenteric artery, gizzard, intestine, rectal caecum and kidney--NA concentrations were much higher than those of AD or DA. The ratios of NA:AD:DA were approximately 100:10:1 for all tissues except spleen, in which DA represented about 10% of the total catecholamines. In the paravertebral chain, the ratio of NA:DA was about 4:1, with no consistent segmental differences. Ganglionic AD was generally less than 1% of the total catecholamine, but isolated ganglia sometimes contained quite large amounts of AD. This AD was probably in chromaffin cells. The results obtained indicate that, contrary to some previous reports, NA constitutes the predominant sympathetic neurotransmitter in the fowl, and neurons in which AD is a transmitter are rare or absent. Although the relatively large amounts of DA present in the ganglia could be due to presence of dopaminergic neurons, no evidence for peripheral projections of such neurons was obtained.