The impact of beta-adrenergic blockade on daily rhythms of melatonin and body temperature of golden spiny mice Acomys russatus.

Beta-adrenergic stimulation induces melatonin synthesis and non-shivering thermogenesis (NST) in rodents. The golden spiny mouse, Acomys russatus is a nocturnal species capable of diurnal activity when coexisting with its congenitor the common spiny mouse A. cahirinus. We have investigated the impact of beta-adrenergic blockade on 6-sulphatoxymelatonin (6-SMT--a metabolite and index of melatonin production) and body temperature (Tb) daily rhythms in male A. russatus. Mice were acclimated to an ambient temperature (Ta) of 28 degrees C, under two photoperiod regimes (16L:8D; 8L:16D). The daily rhythms of Tb and urinary 6-SMT were measured for a period of 30 h at intervals of 4 h. Propranolol (4.5 mg/kg, i.p.) was administered one hour before lights went off (i.e. when beta blockade does not affect NST in this species) and both variables were measured for another 30 h. The beta blocker markedly augmented melatonin output of A. russatus under both photoperiod regimes. The elevation in melatonin secretion was accompanied with an increase in Tb of only 16L:8D-acclimated mice (i.e. shorten duration of melatonin peak). However, in 8L:16D-acclimated mice, a phase advance of about 4 h was noted in 6-SMT daily rhythm. These results indicate that the role of sympathetic innervation in regulation of melatonin synthesis in A. russatus differs from that in the rat. In addition, these data are compatible with the hyperthermic action of melatonin in this species. Therefore, it is suggested that in A. russatus, other neural pathways are involved in its pineal regulation.