Dietary glycine inhibits bladder activity in normal rats and rats with spinal cord injury

Purpose: The influence of dietary glycine on bladder activity, and on glutamate and glycine levels in the serum and lumbosacral cord was examined in rats with or without spinal cord injury (SCI). Materials and Methods: A total of 84 female rats were divided into an intact and an SCI group. Each group of rats was divided into 7 subgroups. Two intact and 2 SCI subgroups were fed a standard diet and the remaining subgroups were fed diets containing 0.1% to 3% glycine. After 4 weeks isovolumetric cystometry was performed with rats under urethane anesthesia. Following cystometry glutamate and glycine levels in the serum and lumbosacral cord were measured as well as the glycine receptor alpha1 mRNA level in the lumbosacral cord. Results: Dietary glycine (1% to 3%) prolonged the interval between bladder contractions in intact rats but did not change the amplitude of contractions. On the other hand, dietary glycine (1% to 3%) prolonged the interval and decreased the amplitude of bladder contractions in SCI rats. The glycine levels in the serum and lumbosacral cord of SCI rats on the standard diet were respectively 43% and 45% lower than those in intact rats on the standard diet. Dietary glycine (1% to 3%) increased the serum glycine level in intact and SCI rats but the glycine receptor alpha1 mRNA level in the lumbosacral cord was unchanged. Conclusions: Dietary glycine crosses the blood-brain barrier and inhibits the micturition reflex pathway in the lumbosacral cord but SCI and/or dietary glycine do not influence glycine receptor expression.