Plasma levels and secretion rate of steroids with anabolic activity in man

Abstract

Both the gonads and the adrenal cortex secret steroids with anabolic activity. It should be realized that the most intense anabolism occurs during infancy and childhood at which time the concentration of steroid hormones with anabolic activity is extremely low. By far the most important anabolic steroid is in testosterone followed by androstenedione, androsterone and dehydroepiandrosterone. Also, estrogens have a generalized anabolic effect, although these hormones have their greatest anabolic action in their respective target organs. In males, after a short period of relatively high T levels immediately after birth, T levels during infancy and childhood are low (+/- 20--30 ng/100 ml); the increase of T levels in one of the first objective signs of puberty and over a period of 3--4 years adult T levels are reached. The latter vary between 380 and 1,000 ng (mean 660 ng/100 ml); the increase in the protein-free, non-protein bound testosterone is even more impressive as the concentration of testosterone binding globulin decreases sharply at puberty. Testosterone levels remain constant up to the 7th decade of life, and decrease rapidly thereafter; free testosterone levels decrease already after the age of 40. T secretion rates in adult males vary between 4 and 10 mg/24 hrs (-/m: 6.6 mg/24 hrs); in males over 65 years the mean T secretion is 4.2 mg/24 hrs: this decrease is a consequence of a decrease in plasma levels and a slowing down of the metabolism. T in adult males originates practically exclusively from the testes. Decreased T levels and secretion rates are observed in hypogonadism and under stressful conditions (anaesthesia, anxiety, hangover, exhaustion, undernutrition) as well as ACTH stimulation. DHT levels parallel generally T levels. Androstenedions (A) in adult males originates in about equal parts from the testes and adrenals. Androstenedione production rates in adult males vary between 1.4--2.1 mg/24 hrs. Dehydroepiandrosterone (DHEA) levels are low in infants and young children. They increase in the immediate pre-pubertal period to reach adult levels after completion of puberty. ACTH as well as stressful situations increase DHEA levels. The mean DHEA production rate is +/- 70 mg/24 hrs. Androsterone is a metabolite of T, A, DHEA, and 170HP, and circulates in plasma essentially as the 3-sulphate and to a lesser extent as the 3-glucuronide. In females, androgen levels before puberty are grossly similar to levels in male children. Pre- and post-menopausal levels of T, DHT, DHEA and their rates of production are discussed. Estrogens have also some anabolic effects. Levels of estradiol (E2) and estrone (E1) in cycling and post-menopausal women are also given. In post-menopausal women E2 levels are extremely low. E2 production rates in post-menopausal women are of the order of 5--20 mug/24 hrs. Progesterone does not appear to have an anabolic effect...