Pharmacology of procaine in the horse: procaine esterase properties of equine plasma and synovial fluid.

This study examines the behavior of the drug procaine in horse blood, plasma, and synovial fluid. The researchers found that procaine is hydrolyzed at different rates in these bodily fluids, and these rates can be affected by a variety of factors.

Key Findings

• The research found that procaine, when added to whole horse blood or diluted plasma, was hydrolyzed with half times of about 9 and 12 minutes respectively at 37 degrees Celsius.
• The hydrolytic activity, which refers to the process of chemical breakdown due to reaction with water, was found to be sensitive to heat and the chemical physostigmine. However, it did not affect another drug called procainamide.
• The study revealed that the rate of the hydrolytic reaction depended on the concentrations of plasma or procaine in the system. It was observed that this rate was less in whole blood compared to plasma.

Role of Plasma Esterases

• The characteristics observed by the researchers suggest that the hydrolysis is likely due to plasma esterases, which are enzymes that catalyze the splitting of esters into an acid and an alcohol in a chemical reaction with water.
• These plasma esterases operated at less than saturating procaine concentrations, meaning they weren’t fully utilized.
• These esterases were also found to be inhibited by cooling and by chemicals such as sodium fluoride and arsenite.

Synovial Fluid

• Synovial fluid, the lubricating liquid in joints, was found to have about 20% the amount of procaine esterase activity compared to plasma.

Comparison Between Breeds

• The researchers also compared the hydrolytic activities in the blood plasma of different horse breeds – Thoroughbred, Standardbred, and other breeds.
• They found statistically significant differences in the rates at which individual plasmas hydrolyzed procaine, indicating that procaine could affect different breeds differently.
• Despite these differences, a frequency distribution of these rates showed a unimodal distribution, meaning that all horses tested may be considered part of a single population in terms of their metabolic handling of procaine.