Abstract
Crossbred ewes exposed to long days for 46 months prior to photoperiod reversal showed no alteration in the duration or amplitude of the circulating melatonin peak between 24 and 46 months of continuous long day exposure. By 3 months after photoreversal to short days, both the amplitude and duration of the peak had adapted to the new scotophase. In short day treated ewes, the melatonin peak was abolished by 46 but not 24 months of short day exposure, and was not fully restored in all ewes 3 months after photoreversal. Mean prolactin levels over 24 h remained high up to 46 months of long day treatment, and declined 3 months after short day exposure. Conversely, mean prolactin levels remained low up to 46 months of short day treatment, increasing 3 months after exposure to long days. Thus: (i) depletion of the melatonin-synthesizing capability of the ovine pineal gland by prolonged exposure to long nights is not completely reversed after 3 months of continuous long day exposure, and (ii) a nocturnal melatonin peak is not essential for maintenance of plasma prolactin levels under these conditions.
Similar content being viewed by others
References
Axelrod, J. 1974. The Pineal Gland: A Neurochemical Transducer. Science 184:1341–1348.
Klein, D. C., Weller, J. L., and Moore, R. Y. 1971. Melatonin metabolism: Neural regulation of pineal serotonin: Acetyl Coenzyme A N-acetyltransferase activity. Proc. Nat. Acad. Sci. USA. 68:3107–3110.
Mori, Y., and Okamura, H. 1986. Effects of timed melatonin infusion on prolactin secretion in pineal denervated goats. J. Pineal Res. 3:77–86.
Williams, A. H. 1981. Some observations of the involvement of the pineal gland in the control of natural wool shedding by Wiltshire Horn sheep. Pages 37–40,in Hudson, P. R. W. (ed.), AWHCON 81, Australian Wool Corporation, Sydney.
Lincoln, G. A., Klandorf, H., and Anderson, N. 1980. Photoperiodic control of thyroid function and wool and horn growth in rams and the effect of cranial sympathectomy. Endocrinology. 107:1543–1548.
Kennaway, D. J., Dunstan, E. A., Gilmore, T. A., and Seamark, R. F. 1984. Effects of pinealectomy, oestradiol and melatonin on plasma prolactin and LH secretion in ovariectomised sheep. J. Endocr. 102:199–207.
Maxwell, C. A., Rintoul, A. J., Foldes, A., Downing, J. A., Scaramuzzi, R. J., and Carter, N. B. 1989. Seasonal modification of ovine pineal function 2: Steroidal effects on melatonin and prolactin profiles. Neuroendocrinology 50:274–279.
Morgan, P. J., Williams, L. M., Davidson, G., Lawson, W., and Howell, E. 1989. Melatonin receptors on ovine Pars Tuberalis: characterization and autoradiographical localization. J. Neuroendocrinol. 1:1–4.
Fraser, S., Cowen, P., Franklin, M., Franey, C., and Arendt, J. 1983. Direct radioimmunoassay for melatonin in plasma. Clin. Chem. 29:396–397.
Slebodzinski, A. B., and Wallace, A. L. C. 1977. Pituitary and thyroidal responses to synthetic thyrotropin releasing hormone in two breeds of cattle. J. Endocr. 75:1–13.
Maxwell, C. A., Foldes, A., Scaramuzzi, R. J., Carter, N. B., and Downing, J. A. 1989. Seasonal modification of ovine pineal function 1: Interaction of gonadal steroids and sympathetic innervation on Beta-adrenoceptors. Neuroendocrinology 49:65–70.
Foldes, A., Rintoul, A. J., Maxwell, C. A., and Scaramuzzi, R. J. 1987. Effects of modifying pineal function on plasma melatonin and prolactin in sheep. Neuroscience 22(Suppl.):471P.
Foldes, A., Maxwell, C. A., Rintoul, A. J., Scaramuzzi, R. J., and Baker, P. 1990. Effects of melatonin implants on selected hormonal profiles and wool growth in Merino wethers. Proc. Aust. Soc. Animal Prod. 18:208–211.
Author information
Authors and Affiliations
Additional information
Special issue dedicated to Dr. Lawrence Austin.
Rights and permissions
About this article
Cite this article
Foldes, A., Maxwell, C.A., Carter, N.B. et al. Effects of prolonged artificial photoperiod on circulating prolactin and melatonin levels in seasonal ewes. Neurochem Res 16, 693–697 (1991). https://doi.org/10.1007/BF00965557
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00965557