I posted several studies on low-ish doses of caffeine raising testosterone and DHT. The mechanism was increase in 5-AR activity. This study claims that substances that raise levels of cAMP have andromimetic properties on the testes. Of all natural substances caffeine is by far the most powerful booster of cAMP. This specific study used theophylline, which I believe is a metabolite of caffeine and occurs on its own in some natural foods like tea and cocoa.
http://www.sciencemag.org/content/168/3928/261.abstract
"...Administration of adenosine 3',5'-monophosphate with theophylline produced testosterone-like induction of hexokinase, phosphofructokinase, pyruvate kinase, and glucose-6-phosphate dehydrogenase in the seminal vesicles of both orchidectomized and immature rats. The N6-O2'-dibutyryl analog of this cyclic nucleotide produced greater increases in vesicular enzyme activities than those induced by the parent compound. The observed enhancement of the key glycolytic enzymes and of hexose monophosphate shunt dehydrogenase was significantly inhibited by actinomycin D and cycloheximide. The evidence indicates that cyclic adenosine monophosphate may be involved as an intermediary in the action of androgenic hormones on male accessory sex organs."
http://www.sciencemag.org/content/168/3928/261.abstract
"...Administration of adenosine 3',5'-monophosphate with theophylline produced testosterone-like induction of hexokinase, phosphofructokinase, pyruvate kinase, and glucose-6-phosphate dehydrogenase in the seminal vesicles of both orchidectomized and immature rats. The N6-O2'-dibutyryl analog of this cyclic nucleotide produced greater increases in vesicular enzyme activities than those induced by the parent compound. The observed enhancement of the key glycolytic enzymes and of hexose monophosphate shunt dehydrogenase was significantly inhibited by actinomycin D and cycloheximide. The evidence indicates that cyclic adenosine monophosphate may be involved as an intermediary in the action of androgenic hormones on male accessory sex organs."