High repeatability of the amplitude and duration of the nycthemeral rhythm of the plasma melatonin concentration in the Ile‐de‐France ewe

Abstract

In order to determine individual variability in the amplitude and duration of the nycthemeral rhythm of the plasma melatonin concentration, 12 ovariectomized estradiol-treated Ile-de-France ewes were submitted to a sequence of 34 long days (LD1, 16L:8D), 21 short days (SD, 8L:16D), and 21 LD (LD2). Intensive blood sampling (hourly from 1 hr before dusk to 1 hr after dawn) was performed for 4 consecutive nights in each of the photoperiodic situations (LD1, SD, LD2), i.e., a total of 12 nights per ewe. Plasma melatonin was assayed by radioimmunoassay. Instantaneous amplitude (difference between each hourly measurement of the plasma melatonin concentration during the nocturnal elevation and the mean diurnal melatonin concentration), mean individual amplitude (same definition but using the mean melatonin concentration during the nocturnal elevation) and duration of elevation of plasma melatonin concentrations were calculated for each ewe and each night and analyzed by variance analysis. Instantaneous amplitude varied significantly with photoperiod, with night intra-photoperiod, with ewes, and time intra-night. Mean individual amplitude varied significantly with photoperiod and with ewe but not with night intra-photoperiod. Dramatic differences between individuals appeared in the amplitude and duration of melatonin rhythms. The lowest mean individual amplitude (all nights of measurement) found was 95 pg/ml and the highest was 544 pg/ml. Overall repeatability coefficient of the mean amplitude of melatonin elevation was 0.71 (P < 0.001). Duration of melatonin elevation varied significantly with photoperiod, with nights intra-photoperiod and with ewes. During LD periods, mean duration of melatonin elevation was equivalent to duration of the night (from 7 to 8 hr), while during SD it varied with ewes from 9 to 16 hr. Repeatability coefficient of the duration of melatonin elevation in SD was 0.57 (P < 0.05). It is concluded that amplitude and duration (in SD) of the nycthemeral rhythm of the plasma melatonin concentration are highly repeatable individual characteristics in the ewe.

Genetic variability in melatonin secretion originates in the number of pinealocytes in sheep

“…In sheep, it has been clearly shown that nocturnal plasma melatonin concentrations is a very stable and highly repeatable characteristic within each ewe (Chemineau et al 1996), and estimation of the heritability coefficient of this trait showed that this between-individual variation in melatonin secretion is under strong genetic control (Zarazaga et al 1998a). Similar findings were obtained in humans concerning melatonin in urine (Wetterberg et al 1983).…”

“…The Ile-de-France breed used in this study results from crossbreedings performed in France between 1830 and 1900 between the English Dishley (Leicester) and Merinos Rambouillet (imported from Spain in the 18th century) breeds (Perret 1986). The Ile-de-France breed was chosen because it was known that the large variability in the nocturnal plasma melatonin concentrations among ewes (Chemineau et al 1996) is under a strong genetic control (Zarazaga et al 1998a,b). It is therefore a good model to study the genetic plasma melatonin variability in mammals (Chemineau et al 2001).…”

Amplitude of the plasma melatonin nycthemeral rhythms is not associated with the dates of onset and offset of the seasonal ovulatory activity in the Ile-de-France ewe

“…In the female Italian Buffalo a significant relationship between the mean nocturnal melatonin concentration and seasonal breeding activity has also been described: animals that show low seasonality, show reduced levels of melatonin concentrations at night [15]. However, whatever the mammalian species and especially in sheep, it is well established that nocturnal melatonin concentrations are highly variable among individuals [16][17][18], and highly repeatable within individuals [19], a large part of the between-individual variability being under a strong genetic control [20].…”

Efeitos da nutrição na atividade cíclica reprodutiva e nas concentrações plasmáticas de melatonina em ovelhas mantidas em pastagem e submetidas ao efeito macho durante o anestro sazonal.

“…(MALPAUX et al, 1988;ARENDT, 1995), mas é estável dentro do mesmo indivíduo (ARENDT, 1995;CHEMINEAU et al, 1996). COELHO (2001) Ainda, no período 3, o horário foi um fator significativo para as concentrações plasmáticas de melatonina.…”

“…Nos ovinos, as concentrações plasmáticas diurnas são baixíssimas (4 a 5 pg/mL), enquanto que as concentrações noturnas são bem elevadas, podendo variar de 100 a 700 pg/mL (ENGLISH et al, 1988;ARENDT, 1995;CHEMINEAU et al, 1996;COELHO, 2001 A interação horário x raça também não foi significativa (P>0,1), não apresentando diferenças no perfil diário médio das concentrações plasmáticas de melatonina entre as raças em cada horário (figura 26). As diferenças aparentes no gráfico no período noturno não são significativas devido a alta variabilidade dos dados e reduzido número de indivíduos dentro de cada raça.…”