title: Diurnal rhythm of melatonin in bovine milk: pharmacokinetics of exogenous melatonin in lactating cows and goats.
abstract: We investigated whether the melatonin levels in bovine milk exhibit a similar daily rhythm as serum levels. In 4 Ayrshire cows at the beginning of the lactation period in May the nocturnal rise in milk melatonin was moderate (from 7 +/- 2 pg/ml at noon to 15 +/- 1 pg/ml at night; mean +/- SEM) and did not correlate well with the melatonin level in serum (from 7 +/- 2 pg/ml to 27 +/- 7 pg/ml, respectively). On the other hand, 6 cows in a later phase of lactation, studied in February, showed a clear long-lasting nocturnal melatonin increase both in serum (from 9 +/- 1 pg/ml at noon to 26 +/- 3 pg/ml at night) and in milk (from 12 +/- 5 pg/ml to 26 +/- 7 pg/ml, respectively). Melatonin kinetics during lactation was studied in more detail in 4 Ayrshire cows and 4 dairy goats by giving an intravenous bolus injection of melatonin. A 3-compartment model with melatonin elimination from the central compartment was used to describe the data. The values (mean +/- SD) for the cows and the goats were: elimination half-life 27 +/- 4 min and 27 +/- 1 min, mean residence time 24 +/- 4 min and 18 +/- 4 min, steady state distribution volume 1.0 +/- 0.3 l/kg and 0.6 +/- 0.1 1/kg (p < 0.05), and plasma clearance 0.044 +/- 0.004 l/kg/min and 0.035 +/- 0.011 l/kg/min, respectively. Following injection, the melatonin concentration in milk increased rapidly and exceeded the corresponding serum value 15-30 min later, remaining thereafter above the serum level. Our results suggest that milk melatonin levels reflect blood concentrations of melatonin with a short delay.
authors.affiliation: Department of Basic Veterinary Medicine, Faculty of Veterinary Medicine, Helsinki University, Finland. Lea.Eriksson@helsinki.fi
authors.forename: L
authors.initials: L
authors.lastname: Eriksson
authors.forename: M
authors.initials: M
authors.lastname: Valtonen
authors.forename: J T
authors.initials: JT
authors.lastname: Laitinen
authors.forename: M
authors.initials: M
authors.lastname: Paananen
authors.forename: M
authors.initials: M
authors.lastname: Kaikkonen
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D019540:Area Under Curve; D002417:Cattle / Q000378:metabolism / Q000502:physiology*; D002940:Circadian Rhythm; D005260:Female; D006041:Goats / Q000378:metabolism / Q000502:physiology*; D006207:Half-Life; D007774:Lactation / Q000378:metabolism*; D008550:Melatonin / Q000097:blood / Q000493:pharmacokinetics*; D008892:Milk / Q000378:metabolism* / Q000502:physiology; D011247:Pregnancy; D011863:Radioimmunoassay / Q000662:veterinary; D012621:Seasons
chemical_list: D008550:Melatonin