title: Development of 24-hour rhythms in serum prolactin and luteinizing hormone levels in rats neonatally administered melatonin.
abstract: To obtain information on the chronobiological consequences of neonatal melatonin administration to rats, we examined the 24h variations of serum prolactin and luteinizing hormone (LH) levels in 21-, 25-, and 60-day-old male rats injected with 100 microg of melatonin or vehicle on the fifth day of life and kept under light from 08:00 to 20:00 daily. In 21-day-old rats, circulating prolactin varied diurnally in melatonin-treated rats only, showing a maximum at 16:00 and a secondary peak at 08:00. In 25-day-old rats, both vehicle- and melatonin-injected rats exhibited significant time-of-day-related changes in serum prolactin, with 77% of the variation in melatonin-injected rats explained by a single 24h component. Acrophase for prolactin rhythm of melatonin-treated rats occurred at 19:51. At 60 days of age, rats receiving vehicle or melatonin showed similar, significant 24h variations in serum prolactin, with acrophases at 17:31-18:15. Serum LH levels attained a maximum at midnight in 21-day-old rats treated with vehicle and at noon in those injected with melatonin. After a cosinor analysis, 71% of the variation in melatonin-injected rats was explained by a single 24h component, with the acrophase at 11:08. In 25-day-old rats, a complex pattern of serum LH concentration was found, with two maxima in vehicle-injected controls, at noon and midnight, and a maximum at noon together with a plateau from 20:00 to 04:00 in melatonin-treated rats. In 60-day-old rats, the maximum of serum LH was found at noon, with a similar extent showing in vehicle- and melatonin-treated animals. The acrophases were at 10:20 (vehicle) and 10:57 (melatonin) and did not differ significantly from that found in 21-day-old melatonin-treated rats. The results suggest that exposure to melatonin early in life may accelerate maturation of 24h prolactin and LH profiles toward an adult form.
authors.affiliation: Departamento de Bioquímica y Biología Molecular III, Universidad Complutense, Madrid, Spain.
authors.forename: A I
authors.initials: AI
authors.lastname: Esquifino
authors.forename: A
authors.initials: A
authors.lastname: Arce
authors.forename: M A
authors.initials: MA
authors.lastname: Villanúa
authors.forename: D P
authors.initials: DP
authors.lastname: Cardinali
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D002940:Circadian Rhythm / Q000187:drug effects* / Q000502:physiology; D007279:Injections, Subcutaneous; D007986:Luteinizing Hormone / Q000097:blood*; D008297:Male; D008550:Melatonin / Q000008:administration & dosage*; D011388:Prolactin / Q000097:blood*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D011388:Prolactin; D007986:Luteinizing Hormone; D008550:Melatonin