Neuroendocrine effects on adrenal hormone secretion in carp (Cyprinus carpio)

The responses of interrenal and chromaffin tissues of carp to acetylcholine (Ach) and its agonists/antagonists were studied in an in vitro perifusion system of head kidney. There was a dose-dependent release of epinephrine and norepinephrine to Ach between 0.01 and 100 mM added for 15 min to the incubation medium. Cortisol secretion was also stimulated, but the response peaked at 1.0 mM Ach and was attenuated with 10 or 100 mM Ach. The maximal release occurred about 30 min after addition of the transmitter. Nicotine stimulated the catecholamines, but had no effect on cortisol, while carbamylcholine, a nicotinic agonist, increased both the catecholamines and cortisol. Muscarine increased cortisol secretion, but affected catecholamines only at higher doses. In contrast, pilocarpine, a muscarinic agonist, stimulated catecholamines more than cortisol. Atropine was not antagonistic, rather it increased the secretion of catecholamines in a dose-dependent manner, and inhibited the release of cortisol. It is concluded that both tissues are influenced by the autonomic nervous system, with the sympathetic system acting on chromaffin cells and the parasympathetic system acting on interrenal cells. However, the nerve supply cannot clearly be defined by agonists or antagonists as in mammals. There is evidence for paracrine effects, e.g., catecholamines inhibit cortisol release and cortisol influences catecholamine secretion.