Circadian rhythm of plasma growth hormone levels in the pigeon∗∗

This study was supported by the National Research Council of Canada. This paper is No 025 in the University of Guelph Migration Series.

Abstract

The plasma growth hormone (GH) level in the pigeon was assessed by radioimmunoassay during a 24‐hr period of 12‐hr light (photophase) and 12‐hr dark (scotophase). The peak GH level was found to be at 06.00 hr (toward the end of the scotophase or onset of the photophase). Thereafter it dropped to its lowest at 18.00 hr (end of the photophase), thus revealing the existence of a circadian rhythm. This rhythm in plasma GH concentration has been correlated with a corresponding free fatty acid rhythm in the pigeon.

Diurnal changes, free fatty acid levels, lipid mobilization, muscular activity, plasma growth hormone, starvation.

Abstracting keywords:

• Diurnal changes
• free fatty acid levels
• lipid mobilization
• muscular activity
• plasma growth hormone
• starvatio

Notes

This study was supported by the National Research Council of Canada. This paper is No 025 in the University of Guelph Migration Series.

Dept of Zoology, College of Biological Science, Univ. of Guelph, Guelph, Ontario, Canada.