[Renal excretion of urea in the Merino and Steppe fat-tailed breeds of sheep after a short period of fasting]. / Renálna exkrécia mocoviny u oviec plemena merino a u stepných tucnochvostých oviec po krátkodobom hladovaní.

Urea excretion was studied in an experiment with two sheep breeds (steppe fat-tailed and merino) on the second day of fasting when the urea concentration in blood increases in fasting animals. The control group in the two breeds was given free-choice feed and water while fasting sheep were given ad libitum only water. Diuresis in both breeds was steady during the experiment. Glomerular filtration rate was not found to vary, in comparison with the control, although the plasma urea concentration rose in fat-tailed sheep (P less than 0.01) as well as in the sheep of merino breed (P less than 0.001). Fractional excretion of urea decreased in fat-tailed sheep (P less than 0.05) and also in the sheep of merino breed (P less than 0.02) while total output of urea remained steady in fat-tailed sheep but it increased in merino sheep (P less than 0.02). Tubular reabsorption of urea on the second day of fasting was observed to be higher by 65% in merino sheep (P less than 0.001), but in steppe fat-tailed sheep the increase was much higher--by up to 180% (P less than 0.001), in comparison with the control. It was demonstrated by the results that the increased tubular reabsorption of urea contributes to the rise of plasma urea concentration in sheep on the second day of fasting.

[Renal regulation of the excretion of urea in fasting camels]. / Renálna regulácia exkrécie mocoviny u hladujúcich tiav.

Experiments were performed with young two-humped camels exposed to 36-hour starvation with free access to water. The renal functions were measured by the standard clearance method. In spite of the administration of 20 micrograms DDAVP, a higher urine flow rate was recorded in the camels subjected to control measurements (feed intake) than in the fasting period (1.45 +/- 0.06 vs. 0.96 +/- 0.06 ml . min-1, P less than less than 0.001). On the second day of fasting the camels had a significantly reduced glomerular filtration rate (GFR 317.5 +/- 23.2 vs. 170.2 +/- 17.4 ml . min-1, P less than 0.001), urea output (700.5 +/- 62.9 vs. 352.2 +/- 64.7 mumol . min-1, P less than 0.005), and fractional excretion of urea (26.9 +/- 2.8 vs. 17.9 +/- 1.7%, P less than 0.01), whereas their tubular resorption. of urea (Reab urea/GFR) increased (6.28 +/- 0.61 vs. 9.12 +/- 0.82 mumol . ml-1, P less than 0.02). No significant difference was found in the concentration of urea in plasma in the fed camels and in fasting camels (8.55 +/- 0.64 vs. 11.18 +/- 1.09 mmol . l-1, N. S.). The creatinine inulin clearance ratio (C creat/Cin) was 0.92 +/- 0.07 when the animals were fed and 1.17 +/- 0.05 when the animals starved (P less than 0.001); this suggests that the clearance of endogenous creatinine is not suitable for GFR measurement in camels under different conditions of nutrition. The kidneys of camels regulate the excretion of urea during short-time fasting mainly through the reduction of glomerular filtration rate and just partly through an increased tubular resorption.