Androstenedione production and interconversion rates measured in peripheral blood and studies on the possible site of its conversion to testosterone.

Abstract

The present aim of in vivo studies of steroid dynamics in the androgen field is to obtain estimates of the total rate of entry of testosterone and its major precursors such as androstenedione into the general circulation, i.e., the blood production rates (1-7). Also required are the secretion rates of this steroid and its precursors, the relative contributions of these secretions to the blood production rates, and a knowledge of the original anatomical sites of these interconversions and secretions.Previous approaches and solutions to these problems have been questioned because in certain situations, when urinary and blood production rate estimates differ, the total rate of entry of steroid into the general circulation cannot be obtained from urinary studies (6, 7). Also the metabolism of a secreted steroid and the same steroid produced from precursor cannot be regarded as being equivalent (8), which is the basic assumption of one urinary approach (2) and one combined blood and urinary approach (6) used to calculate secretion rates. Presumably, both the production and mode of metabolism of a steroid may vary at different anatomical sites (5,(8)(9)(10).To avoid these difficulties, we have measured production and interconversion rates of testosterone and androstenedione directly in .the peripheral circulation. Because the output of steroids from endocrine glands is into the same circulation,

The effect of obesity on the ratio of type 3 17β-hydroxysteroid dehydrogenase mRNA to cytochrome P450 aromatase mRNA in subcutaneous abdominal and intra-abdominal adipose tissue of women

“…1,25 Nonetheless, given that in obese women the amount of intra-abdominal adipose tissue may increase 10-fold 26 with a proportional increase in the numbers of both preadipocytes and adipocytes 27 and the ratio of type 3 17b-HSD to aromatase mRNA in intra-abdominal adipose tissue may be as high as 6, there is potential for substantial production of testosterone in this adipose tissue deposit.…”

“…Conversion of androstenedione in peripheral tissues accounts for approximately 50% of the testosterone production in normal premenopausal women 1,2 and 100% of estrogen production in postmenopausal women. 3 These conversions, catalysed by 17b-hydroxysteroid dehydrogenase (17b-HSD) and cytochrome P450 arom (aromatase) respectively, have been demonstrated to occur in adipose tissue.…”

Low plasma androgens in women with active or quiescent systemic lupus erythematosus

“…Androstenedione was also decreased compared to the control group, but the difference was not statistically significant (Table 3 ) . Thus, there may be a possible dysfunction in the peripheral metabolism of androstenedione, since circulating testosterone originates mainly from the peripheral reduction of androstenedione in premenopausal women (13); the resulting accumulation of circulating androstenedione could blunt a decrease in the adrenal contribution to its production. However, since ovarian activity can be assumed to be normal in our patients (because they have normal menstrual cycles), ovarian contribution to androstenedione production should be normal.…”

Partial Hypogonadotrophic Hypogonadism: Studies of Pituitary Function and of the Pituitary‐testicular Relationship in Two Patients

“…The pla.sina metabolic clearance rate of testosterone (MCRT) was measured by the constant infusion technique of Horton and Tait (1966) between 0800 and 1100 hours, with the patients fasting and reeunil)ent.…”