Blood testosterone precursors

Neurosteroids are steroids that are synthesized de novo in the central nervous system (androsterone, dihydrotestosterone, testosterone, aUopregnanolone, isopregnanolone, and pregnanole). These steroids are synthesized from cholesterol or from a blood-borne precursor. After the extraction of plasma and cerebrospinal fluids using SPE and derivatization with carboxymethoxime, pentafluorobenzyl, and trimethylsilyl, the derivatized samples were injected into a GC/MS system for quantitative evaluation with a selected-ion monitoring (SIM) method, which was used to maximize sensitivity as only a selected m/z is monitored. Details of the method have been described in Refs. 40 and 41. To analyze neurosteroids in the rat brain, Liere et used a BPX5 column (5% phenyl-95 %... 

The follicular phase covers the development of the follicle, which involves an increase in its size due to an increase in follicular fluid, growth of the ovum (i.e. an increase in the contents of RNA and protein) and an increase in the number of cells that surround the ovum. These cells are of two types, the granulosa and the thecal cells. The role of these cells is to synthesise and secrete the steroid hormones oestrogens (mainly oestradiol). The precursor molecule for their synthesis is cholesterol. There is a division of labour between these cells the thecal cells convert cholesterol into the male sex hormones androstenedione and testosterone, which are released into the blood to be taken up by the granulosa cells where they are converted to the oestrogens (Figure 19.8). For details of pathways, see Appendix 19.1. 

I) Consider three structurally similar Cis steroids —testosterone, an-drostenedione, and dehydroepiandrosterone. Each of these compounds is secreted into the blood stream by glands, and after provoking its biochemical effect, is metabolized and excreted. If the only source of the plasma pool were provided by the glandular secretion of the hormone, then the secretion rate would be used to calculate the plasma concentration. However, the picture in the case of the three Ci steroids is complicated by the fact that the three compounds are peripherally interconvertible. Since both glandular secretion and peripheral conversion of precursors contribute to the plasma pool, the production rate is used to... 

Furthermore Tait and co-workers [322] pointed out the marked difference in the urinary and blood production rates of testosterone obtained in women after injection of radioactive testosterone. He concluded that steroids produced from dehydroepiandrosterone contribute little to the blood production rate of androstenedione and testosterone in normal subjects [403]. According to Tait [324], all the blood production rate of androstenedione in the female and testosterone in the male is due to the same secreted steroid, while the blood production rate of testosterone in the female and androstenedione in the male is due about one-half to the same secreted steroid and one-half to converted precursor. The normal male secretes a ratio of testosterone to androstenedione of about 10 1 and the normal female secretes a ratio of androstenedione to testosterone of about 25 1. 

The use of androstenedione (16.3), as a metabolic precursor of testosterone, to increase athletic prowess is unproved and may lead to detrimental effects, such as elevated blood lipid levels, liver problems, and testicular atrophy.35... 

Some steroids, such as cholic acid, progesterone and testosterone were already mentioned in the chapters discussing aldehydes, ketones and carboxylic acids. The most common steroid in humans is cholesterol. Although the compound has been discovered in the eighteenth century its complete molecular structure was determined only in the middle of the last century. Cholesterol appears in most of tissues and it has a special role in the regulation of blood circulation. An imbalance of cholesterol in the organism can cause serious health problems similar to arthero-sclerosis. The cholesterol molecule, like other steroids, is formed by a particular biosynthetic pathway from the terpene precursors, squalene and lanosterol. Since cholesterol has 27 carbon atoms, 3 atoms less than the triterpene squalene (which has 30 C-atoms), 3 C-atoms are eliminated during the biosynthetic process. 

Although cholesterol has a bad reputation, it serves many important ftmctions in the body. Like phospholipids and giycolipids, cholesterol is part of cell membranes. Cholesterol also serves as a starting material (or precursor) for the body to synthesize other steroids such as testosterone, a principal male hormone, and estrogen, a principal female hormone. Hormones are chemical messengers that regulate many body processes, such as growth and metabolism. They are secreted by specialized tissues and transported in the blood. 

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