Faculty Bibliography

The mechanism of the increase in luminal CO2 tension (PCO2) that accompanies jejunal HCO-3 absorption is unknown. One possibility is that mucosal metabolism and the reaction of absorbed HCO-3 with blood buffers in mucosal capillaries govern luminal PCO2. To evaluate this possibility, jejunal segments of anesthetized adult male Sprague-Dawley rats were perfused in vivo with modified Ringer solutions with varying PCO2 levels (0-141 mmHg). Arterial PCO2 was varied by mechanical ventilation (20-70 mmHg). The net flux of CO2 gas into bulk luminal fluid varied directly with the transmucosal PCO2 gradient both in the absence (r = 0.98, P less than 0.001) and presence of net HCO-3 absorption (r = 0.97, P less than 0.001). The apparent permeability coefficient for CO2 gas across the jejunal mucosa was relatively low (2 X 10(-4) cm3 X s-1 X cm length -1) and was not affected by net HCO-3 absorption. Under conditions of equal arterial blood and perfusate PCO2 levels (40 mmHg), the PCO2 in mucosa and effluent was 51 and 44 mmHg, respectively, in the absence and 62 and 48 mmHg, respectively, in the presence of net HCO-3 absorption. These results suggest that CO2 diffuses from the mucosal region into bulk liminal fluid during net HCO-3 absorption in the rat jejunum. In addition, we found in vitro that the elevation of mucosal PCO2 above arterial PCO2 during net HCO-3 absorption can be quantitatively accounted for by metabolism and the admixture of absorbed HCO-3 with blood buffers

To determine the relative effects of systemic pH, PCO2, and bicarbonate concentration on colonic electrolyte transport, states of acute metabolic acidosis and alkalosis were created in Sprague-Dawley rats by gavage feeding (NH4)2SO4 and NaHCO3, respectively. During in situ perfusion of the distal colon in pentobarbital-anesthetized animals, electrolyte transport was measured before and after respiratory compensation of the systemic pH. Acute respiratory acidosis and alkalosis also were studied by ventilating animals with 0, 3, or 8% CO2. When animals in all groups were considered, net sodium absorption correlated well with blood PCO2 (r = 0.99) but not with blood pH. Net bicarbonate secretion correlated with the plasma (r = 0.95) and luminal (r = -0.63) bicarbonate concentrations but not with blood pH or PCO2. Net chloride absorption correlated with both blood PCO2 (r = 0.92) and the plasma bicarbonate concentration (r = 0.80). These results suggest that systemic PCO2 affects a sodium chloride absorptive process and that the plasma bicarbonate concentration affects a chloride absorptive-bicarbonate secretory exchange process in the rat colon

The cardiovascular and renal effects of intravenous (i.v.) and intra-arterial (i.a.) infusions of isoproterenol (ISP, 0.1-0.2 micrograms/kg/min) were evaluated in 17 two-week-old swine anesthetized with pentobarbital. The glomerular filtration rate (GFR) of each kidney and blood flow and vascular resistance (RVR) of the left kidney were determined in all animals. In the 8 animals given ISP i.v., right ventricular pressure and dP/dtmax were also determined via a thoracotomy. In 9 animals, ISP was given i.a. after stabilization of constant-flow perfusion of the left kidney in situ. During i.v. infusion of ISP, the positive inotropic and chronotropic effects and the decrease in arterial pressure were maintained; renal blood flow and GFR increased and RVR decreased. During i.a. infusion of ISP in the constant-flow perfused kidney, similar changes in RVR and GFR were observed despite the higher effective concentrations of drug reaching the kidney. We conclude that, at this stage of postnatal renal development, the infusion of cardiotonic doses of ISP lowers RVR and produces a small increase in GFR.

To determine that relative effects of systemic pH, Pco2, and bicarbonate concentration on colonic electrolyte transport, states of acute metabolic acidosis and alkalosis were created in Sprague-Dawley rats by gavage feeding (NH4)2SO4 and NaHCO3, respectively. During in situ perfusion of the distal colon in pentobarbital-anesthetized animals, electrolyte transport was measured before and after respiratory compensation of the systemic pH. Acute respiratory acidosis and alkalosis also were studied by ventilating animals with 0, 3, or 8% Co2. When animals in all groups were considered, net sodium absorption correlated well with blood Pco2 (r=0.99) but not with blood pH. Net bicarbonate secretion correlated with the plasma (r=0.95) and luminal (r=-0.63) bicarbonate concentrations but not with blood pH or Pco2. Net chloride absorption correlated with blood Pco2 (r=0.92) and the plasma bicarbonate concentration (r=0.80). These results suggest that systemic Pco2 affects a sodium chloride absorptive process and that the plasma bicarbonate concentrations affect a chloride absorptive-bicarbonate secretory exchange process in the rat colon

To determine the relative effects of systemic pH, CO2 tension (PCO2), and bicarbonate concentration on ileal electrolyte transport, states of acute metabolic acidosis and alkalosis were created in Sprague-Dawley rats by gavage feeding (NH4)2SO4 and NaHCO3, respectively. During in situ perfusion of the ileum in anesthetized animals, electrolyte transport was measured before and after respiratory compensation of the systemic pH. Acute respiratory acidosis and alkalosis also were studied by ventilating animals with 0, 3, or 8% CO2. When animals in all groups were considered, net sodium absorption correlated very well with blood pH (r = -0.97). Net bicarbonate secretion correlated with the plasma bicarbonate concentration (r = 0.91) independently of blood pH and PCO2. Net chloride absorption correlated with blood PCO2 (r = 0.92) and was altered when systemic pH and bicarbonate concentration changed in opposite directions. Alterations in luminal pH and PCO2 did not affect electrolyte transport. These results suggest that systemic pH affects a sodium chloride absorptive process and that the plasma bicarbonate concentration affects a chloride absorptive-bicarbonate secretory exchange process in the rat ileum

The effects of acute respiratory alkalosis and acidosis on electrolyte transport in the rabbit ileum, colon, and gallbladder were studied. During in situ perfusion, anesthetized animals were ventilated with 0, 3, or 8% CO2 gas, creating states of alkalosis (pH 7.49 +/- 0.01, PCO2 = 27.0 +/- 0.9 mmHg, HCO3 = 21.7 mM), normocapnia (pH 7.38 +/- 0.02, PCO2 = 41.3 +/- 1.1 mmHg, HCO3 = 25.9 +/- 0.4 mM), and acidosis (pH 7.21 +/- 0.01, PCO2 = 66.3 +/- 1.3 mmHg, HCO3 = 28.1 +/- 0.8 mM). In the ileum alkalosis decreased the net absorption of water (-36%), sodium (-44%), and chloride (-27%), whereas acidosis had the opposite effect on water (+69%), sodium (+98%), and chloride (+32%) absorption and reduced bicarbonate secretion. Small changes in net potassium absorption occurred in the direction of water movement. There was no effect on the ileal transmural potential difference (PD). The colon and gallbladder did not respond to the acid-base disorders with changes in electrolyte transport or PD. These results suggest that systemic pH and/or PCO2 affect an electroneutral sodium chloride absorptive process in the rabbit ileum. The simple presence of this absorptive process in the gallbladder was not a sufficient basis for this organ to respond to alterations in systemic pH