Vol. 277, Issue 5, E792-E797, November 1999
Genetic variability in plasma melatonin in sheep is due to
pineal weight, not to variations in enzyme activities
Steven L.
Coon1,
Luis A.
Zarazaga2,
Benoît
Malpaux2,
Jean-Paul
Ravault2,
Loys
Bodin3,
Pierre
Voisin4,
Joan L.
Weller1,
David C.
Klein1, and
Philippe
Chemineau2
1 Section on
Neuroendocrinology, Laboratory of Developmental Biology, National
Institutes of Health, Bethesda, Maryland 20892;
2 Neuroendocrinologie Sexuelle,
Physiologie de la Reproduction, Institut National de la Recherche
Agronomique, Centre National de la Recherche Scientifique
Unité de Recherche Associée 1291, 37380 Nouzilly;
3 Station d'Amélioration
Génétique des Animaux, Institut National de la
Recherche Agronomique, 31326 Castanet Tolosan; and
4 Faculté Sciences,
Neurobiologie et Neuroendocrinologie Cellulaire, Centre National de
la Recherche Scientifique UMR 1869, 86002 Poitiers, France
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.
pineal gland; arylalkylamine
N-acetyltransferase; hydroxyindole
O-methyltransferase
