Circadian rhythm in Leu-beta-naphthylamide hydrolysing activity in selected photoneuroendocrine areas of adult male rats.

Soluble Leu-beta-naphthylamide hydrolysing activity (arylamidase activity) was assayed in retina, superior cervical ganglia, several brain areas and serum of adult male rats, at different time points of a 12:12h light:dark cycle (from 7h to 19h light). The results demonstrated a left or right biased asymmetrical distribution of this activity depending on the time point studied: While the levels of activity were significantly higher in the left retina than in the right one at 10h of the light period, these were predominant in the right side, at 01h of the dark period. In addition, this activity was higher in the left hypothalamus at 13h of the light period. No asymmetries were disclosed in the rest of time points and structures studied. On the other hand, this activity demonstrated a diurnal variation in the left anterior hypothalamus and total posterior hypothalamus but no periodic variation was evidenced in right anterior hypothalamus or the rest of zones studied. These results may reflect the role of this activity regulating the functional status of its susceptible endogenous substrates.