Seasonal and daily patterns in melatonin secretion in female reindeer and their calves.

Abstract

Daily patterns of pineal function were studied in different seasons in 10 adult semidomesticated female reindeer and 5 prepubertal calves living in a natural arctic environment at latitude 69 degrees 10'N. Serum samples for melatonin RIA were collected every 4 h for 24 h in October (10 h of light, 14 h of darkness and 8 h of light, 16 h of darkness), December (24 h of darkness), March (13 h of light, 11 h of darkness), and June (24 h of light). A significant daily variation in serum melatonin levels was observed in the adult reindeer, with peak values (20-50 ng/liter) occurring during the night in autumn, winter, and spring, but not summer. The daytime values at 13 h (5-10 ng/liter) were constant throughout the year. Total daily amounts of melatonin, the duration of peak levels, and maximal concentrations were significantly lower in spring and summer than before the rut in autumn. The exposure of adult animals to artificial darkness from bright sunlight on August 1 and September 21 resulted in an immediate increase in serum melatonin concentrations. The 2-week-old calves had detectable serum melatonin levels, but no daily rhythm in the spring, whereas a rhythm was detectable by the first autumn, only to disappear unexpectedly during the first winter and return in the spring. At the age of 16 months, the calves had serum melatonin concentrations similar to those in the adults. Our present results show that the continuous illumination experienced during the summer abolished the normal daily melatonin rhythm. This does not seem to be related to organic changes in the pineal gland, since exposure to darkness during the summer increased melatonin levels. The highest melatonin secretion occurred in the autumn and was evidently associated with the rut. Similarly, the daily melatonin rhythm of an adult type observed in the calves at the age of 16 months may be related to the observation that most calves were in rut. Thus, a high rhythmical melatonin secretion appears to relate to puberty and the initiation of heat in female reindeer.

Seasonal changes in melatonin concentrations in female Iberian red deer (Cervus elaphus hispanicus)

“…This agrees with a study by Brainard et al [31] who, in a similar study, also found a higher level in winter in Syrian hamster ( Mesocricetus auratus ). This results contrast with that reported by Eloronta et al [13] in reindeer where a higher melatonin concentrations was observed in autumn, which was not apparently associated with the rut. This might have occurred because all the hinds were cycling in winter whereas only 56.2% were cycling at the rut, as reported elsewhere [26].…”

“…An explanation might be found in the experimental procedure. Eloronta et al [13] found that transferring reindeer indoors into darkness in summer even at mid‐day resulted in an immediate increase in the blood concentrations of melatonin. Thus, a similar effect might have occurred in our study.…”

“…The full characterization of the mechanisms by which the pineal gland mediates the effects of photoperiod through its daily rhythm in secretion of melatonin has been deduced largely from studies in rodents and the domestic sheep [10, 11]. Daily rhythms in the blood concentrations of melatonin, with increased levels at night and low levels during the day have been described in male white‐tailed deer, Odocoileus virginianus , by Bubenik and Smith [12], in female reindeer, Rangifer tarandus , by Eloronta et al [13] and Stokkan et al [14] and in female fallow deer, Dama dama , by Asher et al [15].…”

Endocrine rhythms in the brown bear (Ursus arctos): Evidence supporting selection for decreased pineal gland size

“…Indeed, the apparent absence of a (strong) melatonin rhythm is also consistent with reports in other animals living at extreme latitudes where environmental light cycles disappear during the polar summer and winter (Eloranta et al. , ; Reierth and Stokkan ). However, caution is required in concluding that the melatonin rhythm in bears was completely abolished (vs. masked) because the circadian clock appears functional in bears during hibernation (Ware et al.…”

Circadian Organization of a Subarctic Rodent, the Northern Red-Backed Vole (Clethrionomys Rutilus)

“…Captive willow ptarmigan also became arrhythmic in activity (perch landings) during the near constant light of the Fairbanks, Alaska, summer (West, 1968). Similarly, the constant light of summer caused plasma melatonin rhythms to disappear in female reindeer in Finland (Eloranta et al, 1992). However, not all animals become arrhythmic under the constant lighting conditions of the arctic.…”