16-Ene-steroids in the human testis

Area of Science:

• Endocrinology
• Steroid Biochemistry
• Human Physiology

Background:

• 16-androstenes are boar sex pheromones.
• Human testes metabolize pregnenolone to androsta-5, 16-diene-3 beta-ol (ADL).

Purpose of the Study:

• To identify the unknown metabolite of pregnenolone in human testicular homogenates.
• To investigate the synthesis and presence of 16-androstenes in human testes compared to other species.
• To hypothesize the peripheral synthesis of human sex pheromones.

Main Methods:

• Incubation of human testicular homogenates with [4-14C]pregnenolone.
• Mass spectrometry for metabolite identification.
• Cell culture studies using Leydig cells.
• Enzyme activity assays for 16-ene-synthetase and 5 alpha-reductase in rat, monkey, and human testicular homogenates.

Main Results:

• A metabolite identical to boar sex pheromone precursor androsta-5, 16-diene-3 beta-ol (ADL) was rapidly formed.
• Leydig cells were the primary source of ADL and its metabolite androsta-4, 16-diene-3-one (ADN).
• Human and monkey testes lack 16-ene-synthetase activity, unlike boars.
• Human testes lack 5 alpha-reductase activity, preventing synthesis of 5 alpha-reduced 16-androstenes like androstenol (AL) and androstenone (AN).

Conclusions:

• Human testes synthesize ADL, a precursor to boar sex pheromones.
• The absence of 5 alpha-reductase in human testes suggests peripheral synthesis of AL and AN.
• Peripheral tissues rich in 5 alpha-reductase may convert ADL to AL and AN, potentially serving similar functions as in boars.