GLOMERULAR ACTIONS OF ARGININE VASOTOCIN IN THE IN-SITU PERFUSED TROUT KIDNEY

Recent measurements of plasma arginine vasotocin (AVT) in teleost fish suggest circulating concentrations of 10(-10)-10(-12) M. Previous stu dies of the renal actions of AVT in vivo suggest both diuretic and ant idiuretic effects, but at unknown circulating concentrations. We have investigated the renal actions of 10(-9) and 10(-11) M AVT in vitro us ing an in situ perfused kidney preparation of rainbow trout (Oncorhync hus mykiss). AVT increased vascular resistance (56%), reduced perfusat e flow (P < 0.001), and increased interrenal aortic pressure (P < 0.00 1). AVT resulted in dose-dependent decreases in urine flow rates, glom erular filtration rates, and tubular transport maxima for glucose. AVT at 10(-11) M reduced relative free water clearances (P < 0.01), but u rine/plasma inulin ratios were unchanged, whereas 10(-9) M AVT reduced urine/plasma inulin ratios (P < 0.01) and increased relative free wat er clearances (P < 0.05). The filtering population of glomeruli was re duced by both 10(-11) and 10(-9) M AVT to approximately one-third of t he glomeruli, and a similar population of arterially perfused but nonf iltering glomeruli emerged. These results demonstrate that physiologic al concentrations of AVT have potent glomerular antidiuretic action in the trout, reducing the number of functional glomeruli, and imply red uced individual nephron filtration rates.