Day/night variations in membrane bound leucyl-2-naphthylamide hydrolysing activity in rat anterior hypothalamus, pituitary and retina

Abstract

It is well known that the suprachiasmatic nucleus of the anterior hypothalamus acts as pacemaker regulating circadian rhythms in mammals. The daily variations of neuropeptides as well as their receptors depend on this system (Moore 1983). Aminopeptidases play an important role in regulating the activity of brain peptides (Bauer 1982). In this study we investigated membrane bound leucyl-2-naphthylamide hydrolysing activity in the anterior hypothalamus, pituitary and retina of adult male rats at six time points of a 12:12h light:dark schedule (light from 7:00 to 19:00 h), in order to analyse its day/night variation. The fluorometric assay evidenced significant differences between the three regions: in the anterior hypothalamus being higher during the dark period compared with the light period and in the pituitary higher during the light period compared with the dark period. In the retina the levels of this activity showed a higher heterogeneity during the day. Day – night differences in membrane bound leucyl-2-naphthylamide hydrolysing activity may reflect differences in its susceptible endogenous substrates.

Keywords:

• Leucyl aminopeptidase
• arylamidase activity
• circadian rhythm
• neuropeptides
• photoneuroendocrine circuit

Acknowledgements

We wish to express our thanks to Juan Antonio Madrid of the University of Murcia (Spain) who kindly completed the statistical analysis with the Cosinor test indicated in the polar graphics showed in Figure 2.