Hemorrhage from the inferior vena cava versus the ear artery: a comparison of cardiovascular and hormonal responses in conscious rabbits.

There are inherent complications associated with chronic indwelling venous catheters for use as bleed catheters in long term hemorrhage experiments in conscious animals. As an alternative we have developed a protocol for bleeding conscious rabbits using a disposable catheter in the central ear artery. Previously we had bled rabbits through a catheter chronically implanted in the inferior vena cava (IVC); thus, we were interested in any potential differences in the hormonal (vasopressin and renin) and cardiovascular profile during hemorrhage between the IVC and ear artery bleeds. Rabbits underwent two bleeds, 1 week apart, one using the indwelling IVC catheter and the other with an ear artery (EA) catheter. We compared the mean arterial pressure (MAP), heart rate (HR), plasma vasopressin (AVP), and plasma renin activity (PRA) before and during hemorrhage. Baseline cardiovascular and hormonal values were the same, regardless of choice of bleed site. In addition there were no differences between bleed sites in the rate of fall of MAP (slope: IVC, 0.24 +/- 0.05; EA, 0.26 +/- 0.04) and the rate of rise of HR (slope: IVC, -1.37 +/- 0.22; EA, -1.20 +/- 0.19). Finally the AVP and PRA values associated with a MAP of 50 mmHg (1 mmHg = 133.3 Pa) (close to peak levels achieved during the hemorrhage) were also not different between IVC and EA bleeds. Given that the profiles of the bleeds were not different and that surgical implantation, possible infection, and daily flushing were avoided by the use of the EA catheter, we concluded that use of the EA as a site for bleeding conscious rabbits was justified.