Effects of glycine on hemodynamic responses and visual evoked potentials in the dog.

To study the potential contribution of glycine toxicity in the transurethral resection syndrome, we evaluated hemodynamic and visual evoked potential responses to glycine infusion (1 g/kg) in 22 dogs anesthetized with halothane (1.0–1.2% end tidal). Three dogs received 5% glucose in normal saline without glycine; three received arginine (4 mg/kg) in normal saline without glycine; three received arginine (4 mg/kg) in normal saline without glycine; 10 received glycine (1 g/kg), then arginine (4 mg/kg) 120 min after the completion of glycine infusion; and six received arginine 30 min after the completion of glycine infusion. Arginine was infused to evaluate potential antagonistic effects of glycine toxicity. Blood levels of glycine, ammonia, arginine, urea, and formate were determined after infusions of glycine or arginine. All animals received about 5 ml·kg−1·hr−1 of normal saline during the 2–4 hr of study. Immediately after glycine infusion, cardiac output increased 57%, whereas systemic vascular resistance and mean arterial pressure decreased 32% and 8%, respectively. Later cardiac output and mean arterial pressure were 41 % and 18% less than control levels, whereas systemic vascular resistance returned to control levels. Both amplitude and latency of visual evoked potential waveforms were altered in the animals receiving glycine infusion but not in the control animals. These responses were associated with elevations of blood glycine (149 ± 5 to 9591 ± 809 μM/L, mean + SEM) and blood NH3 (10.5 ± 2.8 to 100.0 ± 13.6 μM/L), but not with formate levels. Infusion of arginine 30 min after the completion of glycine infusion was associated with a reduction of blood glycine levels, but not more than that accountable by the effect of time. Arginine infusion alone in halothane-anesthetized dogs produced no hemodynamic or visual evoked potential waveform changes. However, in the presence of elevated blood glycine and ammonia levels, arginine improved cardiac output and minimized visual evoked potential waveform changes. These results suggest that chemical toxicity from glycine absorption, in addition to water intoxication and hyponatremia, should be considered in the “transurethral resection of the prostate syndrome.”