Prolactin concentrations are not suppressed in mares administered constant exogenous melatonin |
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| Affiliation: | 1. Neurophysiology Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran;2. Department of Physiology, Medical School, Shahid Beheshti University of Medical Sciences, Tehran, Iran;3. Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran;1. Department of Animal Science, Food and Nutrition, Southern Illinois University, Carbondale, IL, USA;2. Department of Surgery and Obstetrics, College of Veterinary Medicine, University of Baghdad, Baghdad, Iraq;3. Department of Animal and Dairy Sciences, Mississippi State University, Mississippi State, MS, USA;1. Sado Marine Biological Station, Faculty of Science, Niigata University, Sado, Niigata 952-2135, Japan;2. Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh, Bangladesh;1. College of Animal Science and Veterinary Medicine, Heilongjiang Bayi Agricultural University, Daqing 163319, China;2. College of Food and Biological Engineering, Qiqihar University, Qiqihar 161000, China |
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| Abstract: | On the summer solstice (June 21, 1996), six of 12 intact light horse mares randomly chosen from a larger herd were subcutaneously implanted with ALZET®a osmotic minipumps containing a melatonin solution (16 mg/ml) designed to release approximately 960 μg of melatonin/day. An additional two mares received implants containing only the saline-DMSO vehicle and four remained untreated. Blood samples were collected on days 5, 26, and 59 of treatment to monitor melatonin concentrations and to verify pump function. Prolactin concentrations were determined from blood samples collected via jugular cannulae every 12 min for 8 hours on days 25,46, and 89 after initial implantation. On day 89, samples were collected hourly for 16 hours following the initial 8-hour sampling period. Melatonin and prolactin concentrations were determined in the blood samples by radioimmunoassay. Mean circulating concentrations of melatonin in treated mares (n=6) were found to be significantly elevated when compared to controls (n=6); however, there was no significant difference in prolactin concentrations between the groups. These studies demonstrate that longterm treatment with melatonin is unaccompanied by a change in prolactin secretion. |
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