Gastrointestinal blood flow in the red Irish lord, Hemilepidotus hemilepidotus: long-term effects of feeding and adrenergic control

Cardiac output, blood flow to the coeliac and mesenteric arteries, dorsal a ortic blood pressure and heart rate were recorded simultaneously at rest an d postprandial for 6 days in a teleost, the red Irish lord (Hemilepidotus h emilepidotus). We anticipated that gastrointestinal blood flow would increa se postprandially, supported by an increase in cardiac output. However, we had no predictions for either the exact time-course of this response, or fo r the regional distribution of blood flow between to the two major arteries comprising the splanchnic circulation. III resting, unfed animals, blood f low to the coeliac artery and mesenteric artery was 4.1 +/- 0.6 ml min(-1) kg(-1) and 4.9 +/- 1.3 mi min(-1) kg(-1), respectively (mean rt SEM, II = 7 ), which together represented 34% of cardiac output. Feeding increased bloo d flow to the coeliac and mesenteric arteries in a time-dependent manner. T he increase ill coeliac artery blood flow preceded that in the mesenteric a rtery, a finding that is consistent with the coeliac artery supplying blood to the liver and stomach, while the mesenteric artery supplies blood to th e stomach and intestine. Coeliac blood flow had increased by 84 +/- 18% aft er 1 day and had a peak increase of 112 +/- 30% at day 4 postprandial. Mese nteric blood flow was not significantly elevated at day 1, but had increase d by 94 +/- 19% at day 4 postprandial. Cardiac output also increased progre ssively, increasing by a maximum of 90 +/- 30% at day 4. Because the increa se in cardiac output was adequate to meet the postprandial increase in gut blood flow, the postprandial decreases in vascular resistance for the coeli ac and mesenteric circulations mirrored the increases in blood flow. Intra- arterial injections of adrenaline and noradrenaline into resting fish more than doubled coeliac and mesenteric vascular resistances, and blood flow de creased proportionately. This adrenergic vasoconstriction was totally aboli shed by pretreatment with the cr-adrenoceptor antagonist phentolamine, whic h in itself approximately halved coeliac and mesenteric vascular resistance s. These observations indicate a significant alpha-adrenergic tone in the g astrointestinal circulation of the red Irish lord, the loss of which could not entirely account for the postprandial increase in gastrointestinal bloo d flow. Other control mechanisms are suggested.