**Core Concept**
Growth hormone (GH) secretion is regulated by a complex interplay of physiological and pathological factors. The hypothalamic-pituitary axis plays a crucial role in GH release, with growth hormone-releasing hormone (GHRH) stimulating and somatostatin inhibiting its secretion.

**Why the Correct Answer is Right**
GH secretion is primarily under the inhibitory control of somatostatin, a hormone produced by the hypothalamus. Somatostatin binds to its receptors on the somatotroph cells of the anterior pituitary gland, reducing GH release. In addition, factors such as high glucose levels, insulin, and cortisol also inhibit GH secretion through various mechanisms. For example, insulin acts on the hypothalamus to stimulate the release of somatostatin, which in turn inhibits GH secretion.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as GHRH stimulates GH release, not inhibits it.
* **Option B:** This option is incorrect as cortisol has a minimal effect on GH secretion and can actually stimulate it in some cases.
* **Option D:** This option is incorrect as high glucose levels can inhibit GH secretion, but it is not the primary factor responsible for decreased GH secretion.

**Clinical Pearl / High-Yield Fact**
Somatostatin analogs are used in the treatment of acromegaly, a condition characterized by excessive GH secretion. These analogs work by inhibiting GH release from the anterior pituitary gland, thereby reducing symptoms such as excessive growth of hands and feet.

**Correct Answer: D. High glucose levels**