It has been generally presumed that circulating catecholamines have little if any effect on systemic vascular resistance in resting trout; however, this question has not been directly addressed. In the present study, the response of isolated vessel rings and perfused tissues to catecholamines and the importance of circulating epinephrine in the vasoconstrictor response of the splanchnic circulation to splanchnic nerve stimulation were examined. Epinephrine (EPI) and norepinephirine (NEPI) produced dose‐dependent contractions of celiacomesenteric (CM) and epibranchial (EB) arteries, anterior cardinal (AC) veins, and increased vascular resistance in the perfused dorsal aorta (PDA; skeletal muscle‐kidney‐distal intestine) and perfused celiacomesenteric (PCM; splanchnic) vascular beds. In all instances the threshold catecholamine concentration for in vitro vasocnstriction was greater than plasma atecholamine concentrations in vivo. Neither EPI nor NEPI contracted ventral aorta rings. Addition of non‐constrictor, but physiological, concentrations of EPI to the perfusate (10‐9M) tripled the increase in PCM resistance produced by splanchnic nerve stimulation. Perfusate EPI also prevented or reversed splanchnic nerve fatigue and restored PCM resistance in fatigued preparations. These results indicate that a direct effect of circulating EPI may be an important source of neuronal catecholamine uptake and may be required to sustain neuronal sympathetic tone. © 1993 Wiley‐Liss, Inc.
ASJC Scopus subject areas
- Animal Science and Zoology