SALIVARY CONCENTRATIONS OF ATRAZINE REFLECT FREE ATRAZINE PLASMA-LEVELS IN RATS

The protein binding of atrazine in plasma and its effect on salivary e xcretion of atrazine was determined in male Sprague-Dawley rats. The d egree of protein binding of atrazine was determined at 3 steady-state plasma concentrations, 50, 150, and 250 mu g/L, using an ultrafiltrati on technique. In total, 48 arterial blood samples were collected from 18 rats; 38 of 48 blood samples had their time-matched whole saliva sa mples. The average protein binding of atrazine ranged from 18% to 37%; however, it was not significantly different across the 3 steady-state plasma concentrations nor among the individual rats. Overall, 26% of atrazine was bound to plasma proteins and not available for transport from blood into saliva. Protein binding of atrazine in plasma was not correlated with total atrazine plasma concentration nor with free atra zine plasma concentration, which indicates that the protein-bound frac tion of atrazine is independent of plasma concentration within the ran ge measured in this study (30-400 mu g/L). The average saliva/plasma ( S/P) concentration ratio of atrazine increased from 0.7 using total at razine plasma concentration to 0.94 (S/fP) when free atrazine plasma c oncentrations calculated as 26% of protein binding was used. Salivary concentration was highly correlated with free atrazine plasma concentr ation. The results suggest that salivary concentration of atrazine not only reflects its total plasma level but accurately measures the port ion of atrazine (free atrazine) in plasma, which may be of toxicologic al significance.