AJP - Regulatory, Integrative and Comparative Physiology, Vol 243, Issue 3 213-R217, Copyright © 1982 by American Physiological Society
Lack of enhanced nocturnal growth hormone release in tethered cynomolgus monkeys
D. L. Bunner, G. A. McNamee Jr, R. E. Dinterman and R. W. Wannemacher Jr
To determine spontaneous 24-h patterns of growth hormone (GH) plasma levels
in unsedated and unrestrained nonhuman primates, a jacket and tethering
system were used to study six cynomolgus monkeys. Hourly blood samples were
collected, and body temperatures were recorded over 24-h periods.
Measurements of GH were made on all samples. In one 24-h study cortisol
levels were also measured as well to document a normal circadian rhythm. GH
was released at mean intervals of 4.5 +/- 0.47 h (mean +/- SE) over the
24-h studies. There were no day-to-night differences in either the mean
interval of GH release (day, 4.6 +/- 0.66 h; night, 4.4 +/- 0.51) or the
mean GH values (day, 9.8 +/- 1.7 mU/l; night, 7.9 +/- 0.8). An apparent
midday peak in GH in the 24-h studies followed feeding. As expected, body
temperature was higher during the day than night, documenting a normal
circadian rhythm. Plasma cortisol also showed a normal circadian variation
with a low point midday and a progressive rise during the night in the one
24-h cycle in which it was measured. GH in unsedated, unrestrained
cynomolgus monkeys was released in 4- to 5-h cycles both day and night
without increased nighttime release. This contrasts sharply with the known
nocturnal sleep release of GH seen in humans.
