Evidence for an endogenous ultradian rhythm governing growth hormone secretion in the rat.

摘要: Sequential blood samples were obtained from undisturbed freely-behaving male rats bearing chronic intracardiac venous cannulae. Blood was withdrawn every 15 min for periods of 4–24 h; plasma separated, and saline-resuspended red cells reinjected. Plasma GH determined by radioimmunoassay. Pulsatile secretion evident in each animal with most peak values >200 ng/ml trough <1 ng/ml. The secretory episodes occurred at approximately 3 h intervals, this rhythmic pattern persisted unchanged across all phases a 12-h lightdark (L-D) cycle. Seven major observed during single 24-h period. mean period, or time interval between episodes, 24 animals 3.32 ± 0.07 (SEM) h. timing the pulses respect to L-D cycle similar animals, indicating that rhythm may be entrained role environmental lighting further assessed 14 exposed constant light 7 wee...