RENAL-FUNCTION AND PLASMA-LEVELS OF ARGININE VASOTOCIN DURING FREE-FLIGHT IN PIGEONS

We examined urinary water loss and plasma levels of arginine vasotocin (AVT) in free-flying, tippler pigeons trained to fly continuously for up to 5 h. First, we used [H-3]polyethyleneglycol ([H-3]PEG) as a glo merular filtration marker by implanting an osmotic minipump into each bird. In two flights (10 birds in winter at an ambient temperature of 13-15 degrees C and seven in summer at 23 degrees C), we measured pre- flight (hydrated, resting control birds) and post-flight [H-3]PEG acti vity and osmolality in blood and ureteral urine. For comparison, we me asured these variables in 10 birds in winter before and after controll ed dehydration (24 h at 25 or 30 degrees C). Second, we measured plasm a levels of AVT in 6-8 birds before and immediately after each of thre e different summer flights. Urine osmolality increased significantly b y up to three times the control level in both post-flight and dehydrat ed pigeons; urine:plasma osmolality ratios did not exceed 2. Compared with controls, glomerular filtration rate (GFR) was significantly lowe r after flight in summer, but did not change in either post-flight or dehydrated winter pigeons. In winter, mean post-flight urine flow rate (UFR) decreased significantly to less than half the control level, wh ile in summer, post-flight UFR did not differ from control levels. In general, mean filtered water reabsorption (Fr-H2O) increased from 95 % in controls to 98 % in post-flight and dehydrated birds. Plasma level s of AVT increased after flight to between three and eight times the p reflight levels. The data from this first study of kidney function dur ing flight are consistent with previous studies of dehydration in bird s and exercise in mammals in which both increased Fr-H2O and decreased GFR contribute to renal conservation of water.