Circadian rhythms in reproductive and thyroid hormones in gonadally regressed male hamsters exposed to natural autumn photoperiod and temperature conditions

Mary K. Vaughan, Armando Menendez-Pelaez, Gerald R. Buzzell, George M. Vaughan, John C. Little, Russel J. Reiter

Research output: Contribution to journalArticle

8 Scopus citations

Abstract

Two groups of young adult male Syrian hamsters were kept in a vivarium at 22°C and a light:dark cycle of 14.5:9.5 h (lights on 06.30 h; indoor) or in a naturally decreasing photoperiod and fluctuating ambient temperature conditions (outdoor) from October 1 (day length 11 h 50 min) to November 30 (day length 10 h 12 min). Representative animals from each group were killed at 3-hour intervals with additional time points near the onset of light. Weights of the paired gonads and accessory organs revealed that all of the animals kept outdoors and none of those kept indoors underwent reproductive regression. Significant circadian rhythms were observed in serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), thyrotropin (TSH), thyroxine (T4), triiodothyronine (T3) and testosterone in indoor and outdoor-housed hamsters. The 24-hour acrophase in serum LH, TSH, T4 and T3 occurred between 13.00 and 16.00 h, while that of serum testosterone and PRL occurred between 18.00 and 20.00 h in indoor hamsters. Hormonal variables in which there was a significant alteration in the 24-hour acrophase of outdoor animals relative to that in the indoor animals included pituitary PRL and serum testosterone, PRL, FSH and TSH. Hamsters housed indoors had a significant rhythm in brown adipose tissue type-11 5′-deiodinase activity, but no rhythm was evident in this tissue in outdoor animals. The natural autumnal conditions depressed serum LH and testosterone around the clock, though the depression of serum FSH relative to indoor hamster values was best seen between 09.00 and 21.00 h and that for PRL between 15.00 and 24.00 h. The overall lower T4 and higher T3 and type-II 5′-deiodinase in brown adipose tissue in the outdoor group suggest a role for accelerated peripheral conversion of T4 in producing the thyroid hormone changes of autumn conditions.

Original languageEnglish (US)
Pages (from-to)96-104
Number of pages9
JournalNeuroendocrinology
Volume60
Issue number1
DOIs
StatePublished - Jan 1 1994

Keywords

  • 5′-deiodinase type-II
  • Adipose tissue
  • Brown adipose tissue
  • Cholesterol
  • Cold exposure
  • Follicle-stimulating hormone
  • Gonadal steroids
  • Gonadotropins
  • Hamster
  • Luteinizing hormone
  • Photoperiod short
  • Prolactin
  • Stress
  • Temperature
  • Testosterone
  • Thyroid hormones
  • Thyrotropin (TRH)
  • Thyroxine
  • Triiodothyronine

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Endocrinology
  • Endocrine and Autonomic Systems
  • Cellular and Molecular Neuroscience

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