Renal Responses to Continuous and Short-Pulse Infusion of Arginine Vasotocin in the Toad Bufo Marinus Available to Purchase

Chronically catheterized specimens of the toad Bufo marinus (L.) were given single bolus injections, periodic bolus injections, and continuous infusions (via peristaltic pump) of the neuropeptide arginine vasotocin (AVT). Urine flow and glomerular filtration rates (GFR) were monitored to quantify the antidiuretic response of the toad to AVT under these conditions. The response to single bolus injections was dissipated after 1 h, despite the continued presence of AVT, whereas continuous infusion of AVT at levels as high as 100 ng kg⁻¹ was ineffective in lowering flow rates, suggesting that pulsatile increases in the hormone might be required to effect a more prolonged response. In toads which were ‘primed’ with AVT via continuous infusion with the pump, additional pulses of AVT were able to lower flow rates for 1 h, with sensitivity to the hormone decreasing with an increase in primed concentration of AVT. Pulses of AVT given to unprimed toads significantly lowered flow for over 2h. This study is the first to show that phasic bursts of AVT are more effective in regulating the renal response of the toad than are continuous, nonpulsatile infusions.