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

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.