Genetic variability in plasma melatonin in sheep is due to pineal weight, not to variations in enzyme activities
Coon, S.L.; Zarazaga, L.A.; Malpaux, B.; Ravault, J.P.; Bodin, L.; Voisin, P.; Weller, J.L.; Klein, D.C.; Chemineau, P.
American Journal of Physiology 277(5): E792-E797
1999
ISSN/ISBN: 0002-9513 PMID: 10567004 Document Number: 508343
The mean nocturnal plasma melatonin concentration (MC) of their parents was used to select two divergent groups each of 25 lambs (from low (L) and high (H) plasma melatonin parents). The MC of lambs was significantly higher in the H group than in the L group (344.1+or-33.0 vs. 189.7+or-24.4 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 (119.1+or-9.2 vs. 83.5+or-6.7 mg, P<0.01) but did not differ between D and N. The amount of melatonin released in vitro per mg 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 between H and L lambs. Hydroxyindole O-methyltransferase activity did not differ significantly between D and N or between H and L lambs. The results showed that genetic difference in MC between the groups of lambs was due to a difference in pineal weight and rather than differences in enzymatic activity of the pineal tissue.