title: Genetic variability in plasma melatonin in sheep is due to pineal weight, not to variations in enzyme activities.
abstract: This study was conducted to determine the origin of the high variability in the mean nocturnal plasma melatonin concentration (MC) in sheep. Two extreme groups of 25 lambs each [low (L) and high (H)] were obtained by calculating their genetic value on the basis of the MC of their parents. The MC of lambs was significantly higher in the H group than in the L group (L: 189.7 +/- 24.4 vs. H: 344.1 +/- 33.0 pg/ml, P < 0.001). Within each group, 13 lambs were slaughtered during the day (D) and 12 lambs during the night (N). Pineal weight was significantly higher in the H group than in the L group (L: 83.5 +/- 6.7 vs. H: 119.1 +/- 9.2 mg, P < 0.01) but did not differ between D and N. The amount of melatonin released in vitro per milligram of pineal gland, the arylalkylamine N-acetyltransferase (AANAT) activity, the AANAT protein content, and the level of AANAT mRNA differed significantly between D and N but not with genetic group. Hydroxyindole O-methyltransferase activity did not differ significantly between D and N or between genetic groups. Therefore, the genetic difference in MC between the two groups of lambs was attributed to a difference in pineal size, not in enzymatic activity of the pinealocytes.
authors.affiliation: Section on Neuroendocrinology, Laboratory of Developmental Biology, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: Coon
authors.forename: L A
authors.initials: LA
authors.lastname: Zarazaga
authors.forename: B
authors.initials: B
authors.lastname: Malpaux
authors.forename: J P
authors.initials: JP
authors.lastname: Ravault
authors.forename: L
authors.initials: L
authors.lastname: Bodin
authors.forename: P
authors.initials: P
authors.lastname: Voisin
authors.forename: J L
authors.initials: JL
authors.lastname: Weller
authors.forename: D C
authors.initials: DC
authors.lastname: Klein
authors.forename: P
authors.initials: P
authors.lastname: Chemineau
mesh_terms: D000121:Acetylserotonin O-Methyltransferase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D002940:Circadian Rhythm / Q000235:genetics; D015870:Gene Expression / Q000502:physiology; D014644:Genetic Variation; D008297:Male; D008550:Melatonin / Q000097:blood* / Q000235:genetics*; D010870:Pineal Gland / Q000033:anatomy & histology* / Q000201:enzymology*; D012333:RNA, Messenger / Q000032:analysis; D011863:Radioimmunoassay; D012756:Sheep
chemical_list: D012333:RNA, Messenger; D000121:Acetylserotonin O-Methyltransferase; D001191:Arylamine N-Acetyltransferase; D008550:Melatonin