Evaluation of Tc-99m-DTPA for renal clearance studies in the pig

Pre-loading large volume oral electrolytes: tracing fluid and ion fluxes in horses during rest, exercise and recovery

KEY POINTS

Exercise results in rapid and large extracellular to intracellular fluid shifts, as well as significant sweating losses of water and ions. It is unknown whether ions within oral electrolyte supplements are taken up by muscle (and other soft tissues) and whether oral supplementation can effectively offset sweating losses. Pre-loading with 8 L of a balanced hypotonic electrolyte supplement attenuated extracellular fluid losses, increased exercise duration and increased sweating fluid and ion losses during submaximal exercise. Supplemented electrolytes appear in skeletal muscle within 1 h after administration. Electrolyte supplementation increased exercise performance, improved maintenance of extracellular fluid volumes, and attenuated body fluid losses while maintaining sweating rates.

ABSTRACT

This study used radioactive sodium (24 Na) and potassium (42 K) in a balanced, hypotonic electrolyte supplement to trace their appearance in skeletal muscle, and also quantified extracellular and whole-body fluid and ion changes during electrolyte supplementation, exercise and recovery. In a randomized crossover design, 1 h after administration of 1 to 3 L of water or electrolyte supplement with 24 Na, horses were exercised at 35% VO2max to voluntary fatigue or, after administration of 8 L of water or electrolyte supplement with 42 K were exercised at 50% peak VO2 for 45 min (n = 4 in each trial). Pre-exercise electrolyte supplementation was associated with decreased loss of fluid and electrolytes from the extracellular fluid compartments during exercise and recovery compared with water alone. The improved fluid and ion balance during prolonged exercise was associated with increased exercise duration, despite continuing sweating losses of fluid and ions. Nasogastric administration of radiotracer 24 Na+ and 42 K+ showed rapid absorption into the blood with plasma levels peaking 45 min after administration, followed by distribution into the extracellular space and intracellular fluid of muscle within 1 h. Following exercise, virtually all Na+ remained within the extracellular compartment, while the majority of K+ underwent intracellular uptake by 2 h of recovery. It is concluded that pre-loading with a large volume, balanced electrolyte supplement helps maintain whole-body fluid and ion balance and support muscle function during periods of prolonged sweat ion losses.

Renal function remains after unilateral total and contralateral partial nephrectomy: an experimental study in pigs using 99mTc-DTPA

Twelve nephrectomies (NEs) were performed in 12 pigs (11-17 kg). Total NE was performed on the left side and partial NE on the right side (lower third of the kidney), thus two-thirds of the total kidney volume was removed. Renal function was studied with 99mTc-diethylenetriaminepentaacetic acid (DTPA) renography and serum urea and creatinine levels preoperatively, and 1 and 2 weeks postoperatively. The pigs were imaged in each session for 30 min by collecting 10-s frames from a posteroanterior (PA) view of an anaesthesized animal. The injected activity was 37 MBq. Serial blood samples were taken from the subclavian vein at 0, 1, 2, 3, 5, 15, 25, 40, 60 and 120 min (six animals) after 99mTc-DTPA injection. The DTPA disappearance rate (DDR) was determined from these samples and in other cases (six animals) a blood sample at 20 min was used. The DDR was also determined from the dynamic gamma imaging data: Regions of interest (ROI) were upper body, spleen, heart and kidneys. The ROI analysis correlated well with the blood sampling data (r = 0.97, P < 0.0001). The reference values for pig DDRs were 0.99 +/- 0.08%/min. These values were 0.71 +/- 0.08%/min at 1 week postoperatively and 0.63 +/- 0.08%/min at 2 weeks. DTPA clearance rates were preoperatively 0.53 +/- 0.06 ml/s; at 1 week postoperatively 0.41 +/- 0.06 ml/s; and at 2 weeks 0.35 +/- 0.06 ml/s. There were no significant differences pre- and postoperatively in creatinine and urea concentrations. The DTPA clearance (ml/s) and disappearance rates (%/min) when determined per kidney area (cm2) increased significantly (P < 0.001 at both 1 and 2 weeks); in 11 of 12 animals the function of the resected right kidney was higher than the split function of the whole right kidney preoperatively. Unilateral nephrectomy initiates a functional adaptation or a growth response in the contralateral kidney to compensate for the loss of a renal mass. These data also indicate that two-thirds of the kidney volume in young pigs can be removed without danger.