Responses of hepatic blood flows to changes in intake in sheep: a meta-analysis

Abstract

This work set out to establish the response equations for hepatic blood flows in sheep and the contribution of hepatic arterial flow to hepatic venous blood flow due to changes in intake levels at constant diet composition. The FLORA (FLuxes across Organs and tissues in Ruminant Animals) database was used, and meta-analysis performed. The meta-analysis involved selection of published papers, identification of studies, description and coding of the selected dataset and statistical analysis using a covariance model. Meta-analyses were carried out using a within-study approach. To ensure absence of bias, the analysis incorporated interfering variables and factors studied in between-study comparisons. Variables concerned diet composition; qualitative factors concerned the physiological state of the animals and the methods used to measure blood flow. The results obtained showed that hepatic blood flows were positively related to intake in sheep. The magnitude of the response (as indicated by the slope) varied with the level of intake and the blood vessel (portal, hepatic venous or arterial). Nine linear relationships were established for the portal, hepatic venous and arterial blood flows as a function of dry matter intake (DMI) with below-and above-maintenance levels considered separately. Data obtained at below-and above-maintenance levels were considered together and four quadratic relationships were established for hepatic blood flows as a function of DMI. These relationships expressed a strong effect of intake on hepatic blood flows. The contribution of hepatic arterial to hepatic venous blood flow averaged 18.2%, with a wide variability. It did not vary significantly with level of intake. Although in between-study comparisons the arterial/venous blood flow was positively influenced by the organic matter digestibility of the diet, the relationships we obtained were robust. They can be used in models of net hepatic nutrient fluxes to predict variations and absolute values of hepatic blood flows from variations and absolute values of DMI.

Relationship between level of forage intake, blood flow and oxygen consumption by splanchnic tissues of sheep fed a tropical grass forage

“…In agreement with studies where the PDV and ST energetic metabolism in fasted, undernourished and fed animals were compared (Kelly et al., ; Ortigues and Durand, ), or were data compiled from literature were analysed (Bermingham et al., ; Vernet et al., ), a positive response in oxygen consumption by PDV and total ST of sheep at increased forage intake was observed in the present study. Moreover, the variability in oxygen consumption by PDV, liver and total ST was directly related to the variability in blood flow rather than to differences in artery‐venous concentrations of oxygen, which is in agreement with previous findings (Kelly et al., ; Ortigues and Durand, ; Lindsay and Reynolds, ).…”

“…The average values of portal and hepatic venous, and hepatic arterial blood flow, as well as of PDV, total ST and liver oxygen consumption obtained in the present study were within the range of values reported in literature for sheep (Bermingham et al., ; Vernet et al., ). Hepatic acetylation of PAH has been reported in sheep (Katz and Bergman, ) resulting in underestimation of PAH concentration in hepatic vein blood and, consequently, in overestimation of the hepatic artery and hepatic vein blood flows if no deacetylation step was introduced in the analysis.…”

“…The deacetylation step for PAH analysis was not used in the present study, and the hepatic artery blood contributed with an average of 25% to the hepatic vein blood flow, which value is within the range of values reported by Vernet et al. (). Thus, it is likely that only a small proportion of PAH was acetylated by the liver of sheep in the present study.…”

“…Vernet et al. () compiled data from literature and observed that the hepatic artery blood flow, in studies where the deacetylation step was included for PAH analysis, was widely variable, representing (mean ± standard deviation) from 9.2 ± 26.1 to 18.0 ± 6.2% of the hepatic vein blood flow in sheep fed below maintenance. The deacetylation step for PAH analysis was not used in the present study, and the hepatic artery blood contributed with an average of 25% to the hepatic vein blood flow, which value is within the range of values reported by Vernet et al.…”

Adaptations of hepatic amino acid uptake and net utilisation contributes to nitrogen economy or waste in lambs fed nitrogen- or energy-deficient diets

“…However, the recalculations of the net hepatic and splanchnic fluxes using a hepatic arterial blood flow contribution of 0.10 (instead of 0.053) led to no modification of the net hepatic Phe fluxes in the C, LN and LE diets and an alteration of ,0.04 in the net splanchnic Phe fluxes in the same three diets (data not shown). In addition, an absence of significant changes in the contribution of the hepatic arterial to total venous blood flow with intake has been previously shown (Vernet et al, 2005). Lastly, results from Ortigues-Marty et al (1994) and Huntington (1982) have shown that the portal and hepatic blood flows can be measured with a relative standard deviation (r.s.d.)…”