Andrology: Pharmacotherapies for Men Only

Article excerpt

Introduction

Andrology is defined as the area of scientific study concerned with the masculine constitution and the diseases of the human male. This implies especially the study of diseases of the male organs of reproduction and aspects of fertility.

Because of the current demographic trends, andrology increasingly will be concerned with problems of aged males, as well as those males in the "crisis decade" (the 50s) entering into an "andropause," or a putative male climacteric. While many critical issues of health and drug therapy of importance to men are not necessarily restricted to that sex, in this article we will consider only those topics that are exclusive to male patients.

Primary and secondary male structures

The primary reproductive organs of the male are the paired male gonads-the testes-which produce not only the male hormones, or androgens, but also the reproductive cellsthe spermatozoa, or sperm cells. Gonadal function is activated from the pituitary by hormones called gonadotropins.

In turn, the penis (by which sperm is transferred during coitus) and adjunct organs needed for semen secretion (the seminal vesicles and the prostate) are maintained in development and function by the testicular hormone, testosterone.

In embryogenesis, androgens are responsible for normal virilization of the urogenital tract. At puberty, gonadotropins from the anterior pituitary evoke continuing production of androgens, which in turn act locally on the cells of primary tissues and organs to support their development during puberty and to initiate the production of semen. In addition, they support the development of secondary structures in the male genital tract, such as the prostate.

In general, the androgens are responsible for expression of the male phenotype by also acting systemically, influencing development of not only skeleton, skeletal muscles, and dermal structures but also such other diverse structures as the vocal cords.

Texture of the skin as well as hair follicles of the scalp, beard, and body are under the influence of the male hormonal regulation. Size and shape of the skeleton, the nature of its musculature, and the level of body fat and its distribution are influenced to achieve the classical male habitus with its contrasts to the habitus of the female.

Male endocrinology

The androgens are hormones consisting mainly of testosterone and its reduction product, DHT (dihydrotestosterone). Both of these molecules bind to and activate androgen receptors, but DHT has greater affinity for the receptor and thus comprises a more potent androgen.

Conversion of testosterone occurs under the influence of the enzyme known as 5alpha-reductase (5AR), which occurs in two forms. Distribution of this enzyme-its levels and the form present--differ across various organs. It is most abundantly present in the prostate, the skin, and the reproductive tissues and organs, making these areas more vulnerable to the effects of androgens. This explains certain later-life, age-related responses to longterm hormone presence, namely, benign prostatic hyperplasia (BPH) and male-pattern baldness-genetically determined, hormone-dependent alopecia. Excess hair growth in older men on areas other than scalp, such as orifices of ears and nose, is another such effect of longterm androgen action.

Testosterone is the predominant circulating form of androgen, occurring primarily (98%-99%) in the globulinbound form; thus, most of it is unavailable to tissue cells. Another important metabolic route for testosterone is its conversion to estradiol and estrone by enzymes known as the aromatase complex, found most abundantly in adipose tissue, liver, and certain nuclei of the central nervous system. The molecules that have undergone 5-alpha reduction, however, are not susceptible to metabolism to an estrogen.

When the testes diminish their normal output of testosterone, secretion of an androgen from the adrenal cortex, dehydroepiandrosterone (DHEA), may become of increased physiological significance. …