Catecholamine concentrations in the hepatic portal system: effect of surgical stress upon portal levels.

The biological effects of a hormone are dependent on the concentration delivered to the target tissue. This is generally best reflected in the arterial concentration. However, the liver is unique in that it receives substantial additional blood flow from the portal venous system. This may be important in the case of the catecholamines, where extraction or spillover from the splanchnic circulation may occur. In this study we examined portal venous catecholamine concentrations in anesthetized, laparotomized rabbits. We compared the values with simultaneously sampled arterial levels to evaluate the effects of the splanchnic tissues upon a wide range of catecholamine concentrations delivered to the liver during a state of stress. Spillover of norepinephrine and extraction of epinephrine were observed in all rabbits. Mean (+/- SEM) arterial norepinephrine concentrations were elevated, 716 +/- 167 pg/ml (n = 11); mean portal concentrations were 178 +/- 37% higher (p less than 0.01), at 1,425 +/- 301 pg/ml, representing net spillover from splanchnic tissues. In addition, significant extraction of epinephrine was observed; arterial concentrations were 2,144 +/- 580 pg/ml (n = 11). Portal levels were 1,205 +/- 382 pg/ml, 38 +/- 7.45% lower than corresponding arterial concentrations (p less than 0.02). Furthermore, there was a concentration-dependent effect upon norepinephrine spillover; the highest arterial norepinephrine concentrations were associated with the lowest splanchnic spillover. This resulted in a negative correlation between the arterial norepinephrine levels and the percent increase from spillover into the portal vein (r = -0.81, p less than 0.003). We conclude that portal venous catecholamine concentrations are significantly different from arterial levels in anesthetized, laparotomized rabbits over a wide range of concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)