PMID: 6962843Jan 1, 1981Paper

Role of melatonin and circadian rhythms in seasonal reproduction in rams

Journal of Reproduction and Fertility. Supplement
G A LincolnJ Arendt

Abstract

In the ram, changes in daylength influence testicular activity by modifying the release of luteinizing hormone-releasing hormone (LH-RH) and thus the gonadotrophins. To investigate the nature of this response the hourly fluctuations in the circulating levels of prolactin, luteinizing hormone (LH) and melatonin were measured in rams kept under various artificial lighting conditions. In Exp. 1, 8 Soay rams (4 control and 4 from which the superior cervical ganglia had been removed) were exposed to alternating 16-week periods of short days (8L: 16D) and long days (16L: 8D) for over 2 years, and blood samples were collected hourly for 25 h on two occasions. The lighting regimen resulted in marked testicular and endocrine changes in the controls but not in the ganglionectomized rams which had low or undetectable levels of melatonin (less than or equal to 33 pg/ml) and an unusual diurnal rhythm in prolactin. In Exp. 2, 8 intact Soay rams were exposed to an ahemeral lighting regimen of 8L: 28D for 16 weeks; at the end of this period blood samples were collected hourly for 52 h and assayed for prolactin. During the pretreatment period of long days (16L: 8D), the testes became fully regressed. During the 16 weeks of 8L: 28D, redevelopmen...Continue Reading

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