Lesions in the hypothalamus and pituitary stalk affect GH secretion in humans. Magnetic resonance imaging of the central nervous system in subjects with hypopituitarism demonstrate an increased incidence of anterior lobe hypoplasia, attenuation or transec-tion of the pituitary stalk, and formation of an ectopic posterior pituitary lobe at the base of the hypothalamus (41,42). Pituitary stalk transection or total hypophysectomy results in attenuation of the GH response to insulin associated with low or undetectable basal levels of GH (44). The diencephalic syndrome, a disorder frequently associated with lesions of the anterior hypothalamus, is characterized by elevated plasma GH levels and a paradoxical rise in GH secretion following glucose administration, reflecting dysregulation in hypothalamic GH-inhibiting pathways (45).
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