Final answer:
The correct statement is A) Growth hormone secretion is enhanced by sleep and exercise. Sleep and exercise stimulate the release of growth hormone, while IGF-1 activates GH's indirect effects and does not enhance its secretion.
Step-by-step explanation:
Among the choices given, the correct statement regarding growth hormone (GH) secretion is: A) Growth hormone secretion is enhanced by sleep and exercise. Sleep and physical exercise are known to increase the release of GH, positively affecting protein synthesis in muscles and bones. On the contrary, growth hormone secretion is negatively regulated by somatostatin or growth hormone-inhibiting hormone (GHIH), which inhibits its production. While IGF-1 (Insulin-like Growth Factor 1) is indeed activated by growth hormone and supports protein formation, it does not enhance the secretion of GH but rather is a part of the indirect mechanism by which GH exerts its effects on growth. In fact, IGF-1 can provide feedback to reduce GH secretion. Additionally, growth hormone levels tend to decrease with aging, and stress has been found to inhibit its secretion. Therefore, statement C is inversely true, and B does not accurately describe the enhancement of GH secretion.