Effects of melatonin on heat production and enzymatic activity in diurnal and in nocturnal rodents

1. 1. Heat production by means of oxygen consumption (. V o 2 ), and enzymatic activity of malate dehydrogenase (MDH), lactate dehydrogenase (LDH), and glucose-6-phosphate dehydrogenase (G6PDH) were studied in diurnal ( Rhabdomys pumilio) as well as nocturnal ( Praomys natalensis) murids, as a response to melatonin treatment. 2. 2. A significant ( P < 0.001) increase in . V O 2 was noticed in melatonin treated mice of both species at ambient temperatures of T a = 6°C, 25°C, 30°C, 32°C and 34°C, when compared to sham operated mice. A significant ( P < 0.001) increase was also recorded in body temperature ( T b) at T a = 6°C and 25°C. 3. 3. Enzymatic activity was significantly higher: P < 0.01 for MDH and LDH in R. pumilio, P < 0.05 for LDH, and P < 0.01 for MDH in P. natalensis, after melatonin administration when compared to sham operated animals.