Mouse Hepatic Portal Venoconstrictive Response to Vasoconstrictors Is Much Weaker Than That in Rat

We previously reported that the portal venous pressure (PPV) response of perfused mouse livers to various vasoactive agents was much weaker than that of other mammals such as rat, rabbit, and guinea pigs. The purpose of this study was to determine the responsiveness of PPV in in vivo BALB/c mouse to intraportal injections of the 3 major vasoconstrictors of angiotensin II, norepinephrine, and endothelin-1 in comparison with that in Sprague-Dawley rats. In anesthetized spontaneously breathing animals, PPV, systemic arterial pressure, and central venous pressure were directly and continuously measured. The above-mentioned vasoconstrictors were injected into the portal vein as a bolus repetitively at the doses ranging 0.01-100 nmol/kg. A close-dependent increase in systemic arterial pressure in response to each vasoconstrictor was observed similarly in both mice and rats. All vasoconstrictors also caused a close-dependent increase in PPV in both species, but the peak levels in mouse did not reach higher than 7 min Hg, whereas it reached as high as 15-24 mm Hg in rats. Immunostaining for alpha-smooth muscle actin revealed that smooth muscles were distributed substantially in Portal venules of rat but scarcely in that of mouse. In conclusion, PPV response to various vasoconstrictors was limited in anesthetized BALB/c mice, as compared with the anesthetized Sprague-Dawley rats, presumably due to small amount of vascular smooth muscle in mouse portal venules.