title: Diurnal fluctuations in methionine-enkephalin levels in the hypothalamus and preoptic area of the male rat: effects of pinealectomy.
abstract: 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.
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D004723:Endorphins / Q000032:analysis*; D004744:Enkephalin, Methionine; D004745:Enkephalins / Q000032:analysis*; D007031:Hypothalamus / Q000032:analysis*; D008297:Male; D010870:Pineal Gland / Q000502:physiology*; D011301:Preoptic Area / Q000032:analysis*; D051381:Rats; D013739:Testosterone / Q000097:blood
chemical_list: D004723:Endorphins; D004745:Enkephalins; D013739:Testosterone; D004744:Enkephalin, Methionine