Endocrine factors are responsible for approximately 50% of hypogonadal or infertility cases. The remainder is of unknown etiology or the result of injury, deformities, and environmental factors. Endocrine-related hypogonadism can be classified as hypothalamic-pituitary defects (hypogonadotropic because of the lack of LH and/or FSH), primary gonadal defects (hypergonadotropic because go-nadotropins are high as a result of a lack of negative feedback from the testes), and defective androgen action (usually the result of absence of androgen receptor or 5a-reductase). Each of these is further subdivided into several categories, but only a few examples are discussed here.
Hypogonadotropic hypogonadism can be congenital, idiopathic, or acquired. The most common congenital form is Kallmann's syndrome, which results from decreased or absent GnRH secretion, as mentioned earlier. It is often associated with anosmia or hyposmia and is transmitted as an autosomal dominant trait. Patients do not undergo pubertal development and have eunuchoidal features. Plasma LH, FSH, and testosterone levels are low, and the testes are immature and have no sperm. There is no response to clomiphene, but intermittent treatment with GnRH can produce sexual maturation and full spermatogenesis.
Another category of hypogonadotropic hypogo-nadism, panhypopituitarism or pituitary failure, can occur before or after puberty and is usually accompanied by a deficiency of other pituitary hormones. Hyperpro-
lactinemia, whether from hypothalamic disturbance or pituitary adenoma, often results in decreased GnRH production, hypogonadotropic state, impotence, and decreased libido. It can be treated with dopaminergic agonists (e.g., bromocryptine), which suppress PRL release (see Chapter 38). Excess androgens can also result in suppression of the hypothalamic-pituitary axis, resulting in lower LH levels and impaired testicular function. This condition often results from congenital adrenal hyperpla-sia and increased adrenal androgen production from 21-hydroxylase (CYP21A2) deficiency (see Chapter 34).
Hypergonadotropic hypogonadism usually results from impaired testosterone production, which can be congenital or acquired. The most common disorder is Klinefelter's syndrome discussed earlier.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.