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      Diurnal Fluctuations in Methionine-Enkephalin Levels in the Hypothalamus and Preoptic Area of the Male Rat: Effects of Pinealectomy

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          Methionine-enkephalin (met-enk) levels were measured at 09.30–10.30, 16.30–17.30 and 23.30–00.30 h in the anterior hypothalamus-preoptic area (AHPOA), medial basal hypothalamus (MBH), anterior, intermediate and posterior lobe of the pituitary gland of male rats. Met-enk levels in the AHPOA and MBH fluctuated significantly through a 24-hour period; from low levels at 09.30–10.30 h, met-enk in the AHPOA and MBH rose slowly in the afternoon to reach peak concentrations at 23.30–00.30 h. Pinealectomy appears to depress or shift the normally occurring increments in met-enk levels at 23.30–00.30 h in the AHPOA only. Serum testosterone (T) levels displayed an inverse relationship with the met-enk rhythm; high concentrations during the day were associated with low met-enk levels and as T levels decreased to a nadir at 23.30–00.30 h, the met-enk in the MBH and AHPOA attained peak concentrations. Daily changes in serum T levels were not affected by pinealectomy.

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          Author and article information

          S. Karger AG
          26 March 2008
          : 35
          : 1
          : 28-31
          aDepartments of Metabolism and Reproduction, College of Veterinary Medicine, bDepartment of Animal Sciences, cDepartment of Obstetrics and Gynecology, College of Medicine, University of Florida, Gainesville, Fla., USA
          123350 Neuroendocrinology 1982;35:28–31
          © 1982 S. Karger AG, Basel

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          Pages: 4
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