IGF1 and obesity due to melanocortin 4 receptor deficiency: Factors that promote GH secretion include sleep, exercise, stress, hypoglycemia, alpha-adrenergic stimulation, beta-adrenergic blockade, and increased blood amino acids, while factors that inhibit GH secretion include IGF-I, hyperglycemia, aging, obesity, alpha-adrenergic blockade, beta-adrenergic stimulation, increased blood free fatty acids, glucocorticoid excess, and thyroid hormone deficiency (5).