Cold Physiology: Postprandial Blood Flow Dynamics and Metabolism in the Antarctic Fish Pagothenia borchgrevinki

Abstract

Previous studies on metabolic responses to feeding (i.e. the specific dynamic action, SDA) in Antarctic fishes living at temperatures below zero have reported long-lasting increases and small peak responses. We therefore hypothesized that the postprandial hyperemia also would be limited in the Antarctic fish Pagothenia borchgrevinki. The proportion of cardiac output directed to the splanchnic circulation in unfed fish was 18%, which is similar to temperate fish species. Contrary to our prediction, however, gastrointestinal blood flow had increased by 88% at twenty four hours after feeding due to a significant increase in cardiac output and a significant decrease in gastrointestinal vascular resistance. While gastric evacuation time appeared to be longer than in comparable temperate species, digestion had clearly commenced twenty four hours after feeding as judged by a reduction in mass of the administered feed. Even so, oxygen consumption did not increase suggesting an unusually slowly developing SDA. Adrenaline and angiotensin II was injected into unfed fish to investigate neuro-humoral control mechanisms of gastrointestinal blood flow. Both agonists increased gastrointestinal vascular resistance and arterial blood pressure, while systemic vascular resistance was largely unaffected. The hypertension was mainly due to increased cardiac output revealing that the heart and the gastrointestinal vasculature, but not the somatic vasculature, are important targets for these agonists. It is suggested that the apparently reduced SDA in P. borchgrevinki is due to a depressant effect of the low temperature on protein assimilation processes occurring outside of the gastrointestinal tract, while the gastrointestinal blood flow responses to feeding and vasoactive substances resemble those previously observed in temperate species.

Exploring nature's natural knockouts:In vivocardiorespiratory performance of Antarctic fishes during acute warming

“…In comparison with Hb + Antarctic notothenioids, our measurements of routine Q̇in C. aceratus (at 0.8°C, 26.6 ml min −1 kg −1 ) is not as divergent as previously reported. Indeed, routine Q̇is lower (29 ml min −1 kg −1 at −0.5°C: Axelsson et al, 1992), or only marginally higher (24 ml min −1 kg −1 at 0°C: Sandblom et al, 2012; 22 ml min −1 kg −1 at −1.0°C: Franklin et al, 2007), than that previously reported in smaller specimens of the more active, cryopelagic P. borchgrevinki. In a more typically benthic species, Trematomus bernacchii, routine Q̇was lower (17.6 ml min −1 kg −1 ; Axelsson et al, 1992).…”

Effects of coeliacomesenteric blood flow reduction on intestinal barrier function in rainbow trout Oncorhynchus mykiss

“…When faced with an acute stressor, the GBF that normally accounts for 20–30% of cardiac output of an unfed fish, drastically drops. This response has been reported in several different species including O. mykiss (Axelsson & Fritsche, ; Gräns et al ., , ; Sandblom et al ., ) . We confirmed that this response was initiated when subjecting the fish to the standardized acute‐stress protocol that caused intestinal barrier dysfunction in O. mykiss .…”

“…The GBF under resting conditions maintained around 10-40% of cardiac output (Seth et al, 2011). However, during acute stress GBF is known to decrease drastically in various species of fish (Dupont-Prinet et al, 2009;Gräns et al, 2009aGräns et al, , 2009bSandblom et al, 2012) presumably as blood flow is prioritized to other oxygen demanding organs (e.g. brain and muscle tissues) during a fight-orflight response (Farrell et al, 2001;Seth et al, 2011).…”

The Gastrointestinal Circulation: Physiology and Pathophysiology

“…The blood flow responses to food ingestion and digestion have been extensively characterized in the GI tract (144,164,166,171,280,281,514). This response, generally referred to as the postprandial hyperemia, has been described for a variety of species, including humans (325), monkeys (509), pigs (102), dogs (145,508), cats (127), rats (12), snakes (459), and fish (422,436). Studies in conscious animals have revealed a biphasic cardiovascular response to ingestion of a meal, with transient increases in aortic pressure, heart rate, and cardiac output, with either no change or a slight increase in GI blood flow noted during the anticipatory-ingestion phase of digestion (138,508).…”