Proceedings of The Physiological Society

Puerto de la Cruz, Tenerife (2003) J Physiol 548P, P171

Poster Communications

Exhaustion stress and the circadian rhythms of melatonin, corticosterone and phagocytic activity

S.D. Paredes, S. Sánchez, A.B. Rodríguez, R.V. Rial* and C. Barriga

Department of Physiology, Faculty of Science, University of Extremadura, 06071 Badajoz, Spain and *Laboratory of Physiology, Fundamental Biology and Health Science Department, University of Illes Balears, 07071 Palma de Mallorca, Spain

Corticosterone and melatonin are true internal chemical pacemakers of different physiological processes, with both hormones having immunoregulatory effects and a circadian rhythm in most vertebrates (Rodríguez et al. 1999). Also, melatonin, due to its physiological antioxidant properties, acts as a buffer in stressful situations by quenching the adverse immunological effects of stress by way of its circadian release (Maestroni, 1993), whilst corticosterone is thought to be the main glucocorticoid secreted in response to stressful exercise (Simon, 1991). The present work was aimed at evaluating if swimming exercise-induced stress changes the circadian rhythms of melatonin, corticosterone, and phagocytosis in 3-month-old male Wistar rats.

Animals (n = 6) were maintained under a 12 h light and 12 h dark photoperiod and subjected every 2 h over one circadian period to a physical activity, which consisted of free swimming for 2 h and then rotating rod exercise until exhaustion, based on a modified version of the automated Porsolt test suggested by Nomura et al. (1982). Afterwards, they were killed by decapitation, and peritoneal cavity macrophage and plasma samples were taken for comparison with samples from control animals (the same conditions as the stressed individuals but in the absence of stressor). Radioimmunoassay was used to determine plasma levels of melatonin (IBL) and corticosterone (DRG Diagnostics). Prior to the melatonin assay, haemoglobin level of samples was measured to avoid any interference it might cause in the melatonin values. All experiments were carried out according to the guidelines of the European Community Council Directive 89/6091 EEC. Data are expressed as mean values ± S.D. and were compared by Student's unpaired t test. Values of P

Where applicable, experiments conform with Society ethical requirements