Seasonal variations in the nycthemeral rhythm of plasma melatonin in the camel (Camelus dromedarius)

Abstract

Seasonal changes in the pattern of plasma melatonin were investigated in two groups of camels (Camelus dromedarius): 11 adult and six young camels. Animals were subjected to the outdoor conditions of a desert environment. Blood samples were taken at regular intervals of about 3 hr (added to particular samples at 1 hr before then 30 min and 1 hr after sunset, and 1 hr before and 1 hr after sunrise) for 24 hr at both solstices and equinoxes of the year. The plasma melatonin levels steeply increased soon after sunset and remained elevated throughout all the night. Then, melatonin concentrations progressively declined shortly before sunrise and returned to daytime basal levels 1 hr later. There was no seasonal variation in the amplitude or in the offset of the melatonin peak or in the daytime basal levels. The onset of the nocturnal peak was delayed by 2 hr in June at the summer solstice (P < 0.05), which can be related to the changes in night length between the two solstices. A significant effect of age was observed in all seasons. Melatonin levels were higher in the young camel group (fall equinox: P < 0.001; spring equinox: P < 0.01; winter solstice: P < 0.01; summer solstice: P < 0.05). The pattern of melatonin secretion in the camel showed a significant seasonal variation parallel to the photoperiodic changes of the year. The observed decline of melatonin levels during an extra-light pulse in the middle of the night indicates the light control of melatonin synthesis. It is not yet known if, in this low latitude desert region, the seasonal breeding period of the camel is cued by the photoperiod. The data obtained, however, clearly demonstrate that the camel has the capacity to follow and to integrate photoperiodic changes through melatonin changes.

Entrainment of the circadian clock by daily ambient temperature cycles in the camel (Camelus dromedarius)

“…Samples were immediately centrifuged at 1,760 g for 30 min, and then plasma was stored at Ϫ20°C for subsequent melatonin assay. Plasma melatonin levels were determined by radioimmunoassay as already described for the camel (8). The inter-and intra-assay coefficients of variation were 4.4 and 5.5% for 5 pg/ml, 5.9 and 7.2 for 50 pg/ml, and 9.9 and 5.2% for 200 pg/ml, respectively.…”

Daily rhythms of physiological parameters in the dromedary camel under natural and laboratory conditions

“…In the camel, in particular, only a few studies have examined daily rhythmicity, and they focused on individual variables such as body temperature (Bligh and Harthoorn, 1965;Bouâouda et al, 2014;El-Allali et al, 2013), sweat rate (Abdoun et al, 2012), plasma aldosterone (Khaldoun et al, 2002), plasma melatonin (El-Allali et al, 2005), and biomarkers of bone formation (Al-Sobayil, 2010).…”

Influencia de la Melatonina sobre la fisiología y la conducta de ungulados

“…Un ejemplo es lo descrito en camélidos en Arabia Saudita (23°N), donde la concentración máxima en verano llega a los 70 pg/ml y en invierno a los 78 pg/ml (p>0,05), con una diferencia de solo dos horas en la duración la oscuridad entre ambas estaciones (El Allali et al, 2005).…”