Chemineau P, Daveau A, Bodin L, Zarazaga L, Gomez-Brunet A, Malpaux B
INRA Département de Physiologie Animale, 37380 Nouzilly, France.
Reprod Suppl. 2002;59:181-90.
Large inter-individual variability in plasma melatonin concentration at night is a common mammalian trait. In sheep, it varies from < 50 pg ml(-1) to > 800 pg ml(-1) but is very consistent within individuals. This inter-individual variability is under strong genetic control, which depends on melatonin secretion from the pineal gland, but not on melatonin catabolism. This genetic variability does not originate from differences in the synthetic enzymes or from a difference in melatonin secretion per mg of tissue, but from a difference in pineal size, which is highly variable among lambs of the same age and live weight. The genetic difference among lambs is already expressed at birth and is due to a difference in the number of pinealocytes rather than in their size. Pineal size and number of pinealocytes correlate strongly with plasma melatonin concentrations. The variability in pineal mass is not associated with the variability in any other organ (for example, the pituitary). The identification of genetic markers in the genome associated with the size of the pineal gland may lead to identification of genes involved in development of the mammalian pineal gland. Divergent selection of sheep on the basis of plasma melatonin concentrations could be used to constitute a mammalian model for extreme plasma concentrations.
夜间血浆褪黑素浓度存在较大的个体间差异是哺乳动物的一个常见特征。在绵羊中，其浓度范围从小于50 pg/ml至大于800 pg/ml，但个体内部非常一致。这种个体间差异受到强大的遗传控制，这取决于松果体分泌褪黑素，而不是褪黑素的分解代谢。这种遗传变异并非源于合成酶的差异或每毫克组织褪黑素分泌量的差异，而是源于松果体大小的差异，在相同年龄和体重的羔羊中，松果体大小差异很大。羔羊之间的遗传差异在出生时就已表现出来，这是由于松果体细胞数量的差异而非大小的差异。松果体大小和松果体细胞数量与血浆褪黑素浓度密切相关。松果体质量的变异性与任何其他器官（例如垂体）的变异性无关。鉴定与松果体大小相关的基因组中的遗传标记可能会导致识别参与哺乳动物松果体发育的基因。基于血浆褪黑素浓度对绵羊进行差异选择可用于构建极端血浆浓度的哺乳动物模型。
