Lack of circadian change of concentration of C-type natriuretic peptide in rabbit aqueous humor.

PURPOSE To determine whether there is a circadian change of the concentration of C-type natriuretic peptide (CNP) in rabbit aqueous humor. METHODS Forty-one male white New Zealand rabbits were submitted to a 12 h light and 12 dark lighting schedule; lights on was at 0 h, lights off at 12 h. C-type natriuretic peptide was assayed at 3 light (2 h, 6 h and 10 h) and 3 dark (14,18 and 22 h) times. All groups consisted of four animals but two had more animals to increase the power of tests (6 h, n = 12; 22 h, n = 13). Dependence between the two eyes was tested by Pearson's correlation. The mean of two eyes was considered for analysis. Differences in concentration in pg/200 ml were evaluated by one-way ANOVA, t test and COSINOR analysis. RESULTS There were no significant differences between the 6 analyzed groups (one-way ANOVA p = 0.157). Pooled into two groups (light and dark), the C-type natriuretic peptide concentration of the light group was lower, 2.626 +/- 0.92 pg/200 ml compared with the dark group 3.02 +/- 1.16 pg/200 ml but did not reach a significant difference (t test; p = 0.23). COSINOR analysis was not statistically significant (R% = 7.72 p = 0.209). CONCLUSION These data demonstrate that the concentration of CNP in aqueous humor did not show a statistically significant circadian change in rabbits entrained to a 12 h light: 12 h dark lighting schedule.