The Effect of Orally Administered Melatonin on the Seasonality of Deer Pelage Exchange, Antler Development, LH, FSH, Prolactin, Testosterone, T₃, T₄, Cortisol, and Alkaline Phosphatase

Abstract

Five milligrams of melatonin (M) per day was administered orally to four male white-tailed deer on a schedule that mimicked first decreasing and then increasing lengths of natural photoperiod. The following seasonal phenotypic and hormonal responses were observed: Pelage exchange, antler mineralization, velvet shedding, and rutting behavior of experimental animals were advanced by 50-55 days. Prolactin (PRL) levels exhibited a bimodal curve with peaks in May and August, as compared to a monomodal curve of controls (peak in June). Peak FSH levels of M-fed deer were advanced 2 months as compared to controls (June vs August). LH concentrations of both groups reached maxima in July; however, in the experimental group, LH levels declined much faster than in controls and then rose again in October-November. Testosterone (T) concentrations of M-fed bucks were elevated 2 months ahead of controls. Melatonin treatment had no significant effect on seasonal variation of T3, or T4. No seasonal rhythm of cortisol was seen in either group and no detectable effect of M was evident. No statistical differences in levels of alkaline phosphatase were seen between groups, although concentrations in experimental bucks sharply dropped to basal levels two months ahead of controls.

Characterization of prolactin secretion in gray wolves (Canis lupus)

“…deer since wolves generally breed in January and February, a time of increasing day length. This apparent contradiction, however, supports the view of Bubenik et al (1986) who stated that "the recurrent theme characterizing the role of PRL in reproduction is its influence to adapt the reproductive process of a given species to the particular ecological situation. Often this means that PRL will have opposite actions in different species."…”

“…It was more likely, however, that PRL secretion in wolves was photoperiodic, with peak levels occurring just prior to summer solstice. The pattern of the PRL cycle of gray wolves is similar to that of white-tailed deer (Mirarchi et al 1978;Schulte et al 1980;Bubenik et al 1986). In deer, high PRL values are associated with long days and the nonbreeding season whereas low PRL levels occur during the short days of the fall breeding season (Adam et al 1987).…”

“…Oral melatonin decreased PRL levels and advanced reproductive behavior in female red deer (Cewus elaphus; Adam and Atkinson 1984;Adam et al 1987), male white-tailed deer (Bubenik et al 1986), and sheep (Kennaway et al 1982). In wolves, oral melatonin decreased PRL levels in May and June when these were at their highest (Fig.…”

Exploring the mechanisms regulating regeneration of deer antlers

“…The first experiment to demonstrate the link between photoperiod, antler development and the breeding season was undertaken 50 years ago (Jaczewski 1954) and has been confirmed by several later studies (reviewed by Goss 1983). The mechanism whereby the photoperiod is linked to antler growth and reproductive activity is not clear but is likely to involve changes in melatonin secretion from the pineal gland, which then acts on the hypothalamo-pituitary axis (Bubenik et al 1986).…”

Distribution of BDNF and TrkB isoforms in growing antler tissues of red deer

“…During spring, the increase of day length does not activate reproduction, but it is responsible for inducing antler growth, so the mechanism by which the photoperiod is linked to antler growth and reproductive activity is not clear. To date, melatonin secretion from the pineal gland has been claimed to mediate the transmission of photoperiodic information to the hypothalamic-pituitary axis (Bubenik et al, 1986). In mammals, the master circadian pacemaker is localized in the suprachiasmatic nucleus (SCN) of hypothalamus, where brainderived neurotrophic factor (BDNF) immunoreactivity has been observed (Conner et al, 1997).…”