BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 15. INTEGRATION OF METABOLIC PATHWAYS. HORMONES

15.10. Sex Hormones

15.10.1. Synthesis of Male Sex Hormones

The precursor in the synthesis of Sex Hormones is Cholesterol, which is either delivered from the plasma as part of LDL or synthesized within the Cells of the Gonads from acetyl-CoA. The Cleavage of the side chain of cholesterol to form pregnenolone is the rate-limiting reaction that determines the overall rate of hormone synthesis and is stimulated by LH.

The conversion of pregnenolone into testosterone is catalyzed by five microsomal Enzymes. Two pathways for this conversion are known, of which one (via progesterone formation) predominates in human Testes:

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Testosterone circulates in the Blood in a bound state—associated with albumin and a specific β-globulin. Only 2% of the hormone is present in the blood in a free state, and it is precisely these molecules that are biologically active. Testosterone serves as a precursor to a more potent androgen, dihydrotestosterone. This conversion takes place in the seminiferous tubules, Prostate Gland, Skin, and external genitalia through the action of a cytoplasmic enzyme, NADPH-dependent 5α-reductase.

The Physiological effects of androgens vary across different periods of life. As early as the Embryonic Stage of development, androgens significantly influence the differentiation of male gonads and other Tissues. Androgens exert a powerful anabolic effect by stimulating Protein Synthesis. In addition, they promote Cell Division and, during the prepubertal period, lead to a sharp increase in linear body dimensions, Skeletal Muscle mass, and bone growth, while also inducing changes in skin texture and a deepening of the voice.