In vivo evidence for adrenal catecholamine release mediated by nonnicotinic mechanism: local medullary effect of VIP.

The aim of the present study was 1) to develop a model in anesthetized dogs in which local infusion of a given substance could be made to the adrenal gland without any systemic effects and 2) to show in this model the potential existence of a nonnicotinic mechanism involved in adrenal catecholamine secretion. Plasma catecholamine concentrations were determined by an high-performance liquid chromatography method. The local infusion into the left adrenolumbar artery (0.5 ml/min for 1 min) of either dimethylphenylpiperazinium (0.3-3.0 micrograms/ml) or vasoactive intestinal peptide (0.1-10.0 micrograms/ml) resulted in dose-dependent increases in both epinephrine and norepinephrine secretions. Neither aortic pressure nor plasma catecholamine levels altered during the drug infusion. The net increases in adrenal catecholamine secretion obtained with dimethylphenylpiperazinium were abolished by the nicotinic blockade with pentolinium (2 mg/ml, 0.5 ml/min for 2 min). However, the net catecholamine responses to vasoactive intestinal peptide remained unaffected in the presence of the same dose of pentolinium. The results suggest that there exists a nonnicotinic mechanism that may be implicated in the local regulation of medullary catecholamine secretion in the dog adrenal gland. This model may be a useful tool for studying local physiological role(s) of various neurotransmitters and neuromodulators in the adrenal secretory function in vivo.