**Core Concept**
The regulation of the reproductive axis is controlled by the hypothalamic-pituitary-gonadal (HPG) axis, where Gonadotropin-releasing hormone (GnRH) is a key neurohormone that stimulates the secretion of Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH) from the anterior pituitary gland. The pulsatile release of GnRH is essential for the normal functioning of the HPG axis, and alterations in GnRH pulse frequency can lead to various reproductive disorders.

**Why the Correct Answer is Right**
A higher pulse frequency of GnRH leads to an increase in LH and FSH secretion, resulting in an increase in the production of sex hormones. This is because the GnRH receptor is coupled to G-proteins that stimulate the production of cAMP, leading to an increase in LH and FSH secretion. The increased LH secretion stimulates the Leydig cells in the testes to produce testosterone, while the increased FSH secretion stimulates the Sertoli cells in the testes to produce androgen-binding protein (ABP). In females, the increased FSH secretion stimulates the growth and maturation of follicles in the ovaries, leading to an increase in estrogen production.

**Why Each Wrong Option is Incorrect**
**Option A:** A decrease in GnRH pulse frequency would lead to a decrease in LH and FSH secretion, resulting in a decrease in sex hormone production.
**Option B:** A change in GnRH pulse frequency would not affect the secretion of other hormones such as Adrenocorticotropic hormone (ACTH) or Thyroid-stimulating hormone (TSH).
**Option C:** While GnRH is a key neurohormone in the regulation of the reproductive axis, a higher pulse frequency of GnRH would not lead to an increase in blood pressure or heart rate.

**Clinical Pearl / High-Yield Fact**
A higher pulse frequency of GnRH can lead to precocious puberty in children, while a decrease in GnRH pulse frequency can lead to hypogonadotropic hypogonadism.

**Correct Answer:** D.