DIURNAL-VARIATIONS OF SERUM AND TESTICULAR TESTOSTERONE AND DIHYDROTESTOSTERONE (DHT) IN DJUNGARIAN HAMSTERS (PHODOPUS-SUNGORUS) - TESTES ARE THE MAIN SOURCE FOR CIRCULATING DHT

Testes and sera of adult Djungarian hamsters kept in a light:dark cycl e of 16L:8D were collected every 1.5-3 hr for 24 hr. The concentration s of testosterone (T) and its metabolite Scc-dihydrotestosterone (DHT) were estimated by HPLC separation of the steroids followed by radioim munoassay. Both testicular and serum concentrations of T and DHT exhib ited strong diurnal variations (P < 0.001) with highest levels at the end of the light phase, while both hormones declined drastically durin g the dark period. The ratios of DHT/T, as an indicator of the activit y of the enzyme 5 alpha-reductase, were on average 0.39 in the testes and 0.29 in serum. Comparisons of individual data revealed highly sign ificant correlations between testicular and serum concentrations of th e hormones (T:r = 0.87; P < 0.0001; DHT:r = 0.69, P < 0.0001). Likewis e, the individual values of testicular and serum DHT/T ratios correlat ed highly significantly (r = 0.60; P < 0.001). The results indicate th at in Djungarian hamsters the main source of DHT is the testes, while the peripheral conversion of T to DHT seems to be negligible. (C) 1995 Academic Press, Inc.