Chapter 10 The gonads
Introduction
Androgens and testicular function
The testes are responsible for the synthesis of the male sex hormones (androgens) and the production of spermatozoa. The most important androgen, both in terms of potency and the amount secreted, is testosterone. Other testicular androgens include androstenedione and dehydroepiandrosterone (DHEA). These weaker androgens are also secreted by the adrenal glands but adrenal androgen secretion does not appear to be physiologically important in the male. In the female, however, it contributes to the development of certain secondary sexual characteristics, in particular the growth of pubic and axillary hair. The pathological consequences of increased adrenal androgen secretion are discussed in Chapter 8 and on p. 174.
Specific assays are readily available for testosterone, SHBG and the individual adrenal androgens.
Sex hormone-binding globulin
SHBG binds both testosterone and oestradiol in the plasma, although it has greater affinity for testosterone. The plasma concentration of SHBG in males is about half that in females. Factors that alter SHBG concentration (Fig. 10.1) alter the ratio of free testosterone to free oestradiol. If SHBG concentration decreases, the ratio of free testosterone to free oestradiol increases, although there is an absolute increase in the concentrations of both hormones. If SHBG concentration increases, the ratio decreases. Thus in either sex, the effect of an increase in SHBG is to increase oestrogen-dependent effects, while a decrease in SHBG increases androgen-dependent effects (Fig. 10.2).
Disorders of male gonadal function
Delayed puberty and hypogonadism in males

Figure 10.4 A protocol for the human chorionic gonadotrophin (hCG) test for primary testicular failure.
Case history 10.1
Investigations
Serum: testosterone | 3 nmol/L |
LH | <1.5 U/L |
FSH | <1.5 U/L |
Clomifene test (3 mg/kg body weight clomifene citrate daily for 7 days):
Serum: LH | <1.5 U/L |
FSH | <1.5 U/L |
Gonadotrophin-releasing hormone (GnRH) test (100 µg GnRH i.v.):
Time (min) | FSH (U/L) | LH (U/L) |
0 | <1.5 | <1.5 |
20 | 2.0 | 2.0 |
60 | 2.5 | 3.0 |
(after 100 µg GnRH s.c. daily for 2 weeks) | ||
0 | 3.5 | 4.5 |
20 | 8.4 | 21.5 |
60 | 4.5 | 8.0 |
You may also need

Full access? Get Clinical Tree

