title: Fluctuations in peripheral serum testosterone levels within a day, with age and by sexual stimulation in male beagle dogs bred indoors.
abstract: Fluctuations in serum levels of testosterone (T) within a day, both with age and as a result of sexual stimulation, were examined in male beagle dogs. Eighty male dogs aged between 3 months and 16 years and bred in our laboratory were used under strictly controlled breeding conditions (temperature: 22 +/- 1 degree C, relative humidity: 55 +/- 5%, lighting time: 8:00 a.m.-8:00 p.m.). The level of T was measured by an RIA method. In order to examine the fluctuation in T level within a day, blood samples were obtained at 0:00, 6:00, 12:00 and 18:00 in each of five dogs aged 1.7 and 2.1 years. T levels fluctuated with a regular pattern that was lowest at 12:00, and increased to a peak at 18:00-6:00, thereafter decreasing until 12:00. In order to examine the change in T level with age, blood samples were obtained at 9:00, 12:00 and 16:00 from 70 dogs aged between 3 months and 16 years. The regular diurnal pattern of T level was usually seen, and the levels at 12:00 were always low and did not fluctuate at any age except for 6 months, and 13, 14 and 16 years. The T level at 9:00 increased to reach a peak at 4 years, whereas that at 16:00 did so at 2 years. T levels at 9:00 were significantly higher at 4-12 and 14 years than at 3 months, and were higher at 4 years than at 9 months.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Division of Comparative Radiotoxicology, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Fukuda
authors.forename: H
authors.initials: H
authors.lastname: Nagashima
authors.forename: K
authors.initials: K
authors.lastname: Morioka
authors.forename: J
authors.initials: J
authors.lastname: Aoki
mesh_terms: D000367:Age Factors; D000818:Animals; D000830:Animals, Laboratory / Q000502:physiology*; D002940:Circadian Rhythm; D004285:Dogs / Q000502:physiology*; D008297:Male; D012724:Sex Attractants; D012726:Sexual Behavior, Animal / Q000502:physiology*; D013739:Testosterone / Q000097:blood*
chemical_list: D012724:Sex Attractants; D013739:Testosterone