Effect of whole-body pH changes on thoracic duct lymph flow in anesthetized sheep

Physiologic alterations of pH in vitro produce alterations of the oncotic pressure of both plasma and interstitial proteins, the effect being more marked in the latter. Therefore we postulated that by changing an animal's pH we could produce alterations in fluid distribution and affect the whole-body lymph flow rate. To test this hypothesis, we infused seven acutely nephrectomized anesthetized sheep with 2% body weight/volume isosmotic lactated Ringer's solution and bicarbonate (200 mEq) after a 30-minute control period. The fluid was infused over a 10-minute period with 20-minute recovery intervals. To another group of seven ewes, we infused the same volume of lactated Ringer's solution and hydrochloric acid (40 mEq). Throughout the experiment, we continuously measured arterial and venous pressures and lymph flow rate. Every 10 minutes we obtained samples for arterial pH, for hematocrit, and for plasma and lymph protein and osmolality. The infusion of bicarbonate was associated with a comparatively lower peak lymph flow rate (383% over baseline compared with 757% for acid infusion). Also the lymph flow rate after acid infusion started to increase approximately 5 minutes after the beginning of the infusion, as compared with approximately 10 minutes after the base infusion. Acid infusion did not increase arterial pressure, in contrast to the other infusions. The changes in pH obtained with the infusions were insignificant for the Ringer's infusion, +0.17 for the base, and -0.16 for the acid. The plasma/lymph protein concentration ratios at the end of the infusion were no different for acid or base: 112.4% +/- 4.4% and 101.9% +/- 5% (difference from control, mean +/- SEM) respectively (p greater than 0.1). In conclusion, minimal alterations of pH produced alterations in the cardiovascular and lymph flow rate responses to fluid challenge in anesthetized animals.