Portal blood flow in beef steers: comparison of techniques and relation to hepatic blood flow, cardiac output and oxygen uptake.

Abstract

We compared two techniques for measuring blood flow through portal-drained viscera (PDV) of beef steers and measured portions of cardiac output and total oxygen uptake attributable to PDV and hepatic tissues. Four steers (198 +/- 2 kg), equipped with chronic catheters in appropriate vessels, a transit-time ultrasound probe around the hepatic portal vein and a temporary cardiac output thermodilution catheter, were fed a 60:40 hay: concentrate diet. Treatments, designed to alter blood flow, were: 12 equal meals every 2 h (CNTL); CNTL plus 2 mg clenbuterol in one meal (CLEN); and a 65-h fast (FAST). Blood flow through PDV was measured by dilution of p-aminohippurate (PAH) and transit-time ultrasound. Hepatic blood flow was measured by PAH dilution and cardiac output was measured by thermodilution. Blood flow measured by transit-time ultrasound was consistently slower (45%, P less than .01) than blood flow measured by PAH dilution. Necropsy revealed anatomical constraints that precluded proper placement and function of the flow probes. Cardiac output (liters/h) was greater (P less than .05) for CLEN (3,082) than for CNTL (1,655) or FAST (1,047). Percentage of cardiac output flowing through PDV and hepatic tissues was less (P less than .05) for CLEN (23 and 24%) than for CNTL (31 and 38%) or FAST (32 and 38%). Whole body oxygen uptake (mmol/h) was greatest (P less than .05) for CLEN (4,220), intermediate for CNTL (2,999) and least for FAST (1,965). Percentage of oxygen uptake attributable to hepatic tissues was greater (P less than .05) for FAST (31%) than for CLEN (18%), with CNTL intermediate (24%). Percentage of oxygen uptake attributable to PDV (22%) was not affected (P greater than .05) by treatments.

Metabolic responses of the whole body, portal-drained viscera and hindquarter to adrenaline infusion: Effects of nonselective and selective β-adrenoceptor blockade

“…In the dog, the adrenalineinduced increase in oxygen consumption of the jejunum is associated with elevated glucose uptake (Grayson and Oyebola 1983). Additionally, the portal-drained viscera blood flow and metabolic response to adrenaline observed in this study is consistent with functional hyperaemia reported previously by Eldostone and Holzman (1981) and Huntington et al (1990) in circumstances where the gastrointestinal tract of sheep meets its oxygen demand with a comparatively large blood flow response.…”

“…In sheep, the anatomy of the portal vasculature allowed for appropriate placement of the probe. We concur with the suggestion that the portal vein blood flow in sheep could be determined accurately with ultrasound probes [Bergman E.N., cited by Huntington (1990)]. …”

“…However, our values differ somewhat from those from a study with cattle (Huntington et al 1990) in which a poor correlation between PAH dilution technique and transit time was observed. In the latter study, the lack of agreement between the two methods was attributed to anatomical structure of the portal vasculature of cattle and inadequate space to accommodate the probe (Huntington et al 1990). In sheep, the anatomy of the portal vasculature allowed for appropriate placement of the probe.…”

Whole-body fuel selection in ruminants: nutrient supply and utilization by major tissues

“…by 122 (SE 18-2) J/d per kg0.75 for each increment of 1 kJ MEI/d per kg0.75 (from equation 6, Table l), and was partly related to enhanced hepatic 0 2 extraction ratios (equation 9, Table 1). It should not be extrapolated to lower intakes than those used here (<184 kJ/d per kg0.75) since experimental results suggest that a 3 d fast activates hepatic metabolism leading to higher 'basal' energy expenditure (110 kJ; Eisemann & Nienaber, 1990;Huntington et al 1990) than that predicted from the intercept of equation 6 (50 kJ; Table 1). …”

Leadership—Management Superstructure

“…In concordance with Burrin et al [21], these findings showed that liver mass (e.g., reduced cell size and/or number) changed more rapidly than body weight in response to undernutrition, illustrating the ability of these tissues to adapt rapidly to changing nutrient supply. In ruminants, portal blood flow is known to vary with metabolizable energy intake [1,23], thus, in underfed animals, blood flow is reduced, leading to decreased liver nutrient absorption and in consequence a decreased liver mass.…”