Neurophysiological regulation of the secretion of growth hormone.

The regulation of GH secretion involves the harmonious integration of factors acting at the hypothalamic and pituitary levels summating to produce the peripheral patterns of intermittent GH secretion observed in man and experimental animals under physiologic and experimental conditions. SRIH and GHRH act primarily at the pituitary to regulate the secretion of GH, while monaminergic, cholinergic and peptidergic neurotransmitters act centrally and/or at the pituitary level. In addition IGF-I, the anabolic effector of GH has inhibitory feedback effects at both the pituitary and hypothalamus. The control of GH secretion often differs between species and is dependent on the sex, nutritional state and physiologic condition being studied. In vivo and in vitro effects may differ as the complex, multilayered regulatory mechanisms of GH secretion in the intact subject override the direct effects of an individual controlling factor.