ABSTRACT

Melatonin synthesis in the pineal gland shows a circadian rhythm and reaches its maximum level during the phase of darkness. Surgery and anaesthesia affect melatonin secretion and endocrine function. The aim of this study was to investigate the effects of isoflurane anaesthesia during night vs. day on plasma melatonin level in rats.

Twenty–six 15-day-old male rats were included and divided into 4 groups by randomization. Isoflurane (1.5%) was administered between 07:00 pm and 01:00 am (night group) or 07:00 am and 01:00 pm (day group) in winter; 6 L min-1 of oxygen was administered to control groups during the same time periods. At the end of 6 hours the rats were sacrificed and blood samples were taken. Blood samples were centrifuged and plasma melatonin levels were measured by enzyme-linked immunosorbent assay (ELISA).

When Group Gc-I (night-isoflurane) was compared with Group Gc-K (night-control), Group Gc-I with Group Gn-I (day-isoflurane), and Group Gc-K with Group Gn-K (day-control), no significant differences were found in plasma melatonin levels (p=0.132, p=0.180 and p=0.065, respectively). When Group Gn-I was compared with Group Gn-K, plasma melatonin levels were significantly increased in Group Gn-I (p=0.009).

It was concluded that 1.5% isoflurane administered over 6 hours in 15 day old rats increases plasma melatonin levels significantly in the daytime but does not affect them at night.

Keywords: Isoflurane, rat, circadian rhythm, melatonin