DISTRIBUTION OF THE SITE OF 17-ALPHA,20-BETA-DIHYDROXY-4-PREGNEN-3-ONE PRODUCTION IN THE SPERMIATING AMAGO SALMON (ONCORHYNCHUS-RHODURUS) TESTIS

Using four different testicular preparations of spermiating amago salm on, Oncorhynchus rhodurus, we measured three testicular steroids in th e incubation medium by radioimmunoassay. Intact testicular fragments ( intact TF) in response to chum salmon gonadotropin (SGA) produced a la rge amount of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta-DP) and a significant amount of 17 alpha-hydroxyprogesterone, but not 11-ketotestosterone. Sperm-free testicular fragments (sperm-free TF) mainly produced 17 alpha-hydroxyprogesterone in response to SGA. S perm preparations did not produce all three steroids in response to SG A, whereas co-incubation of sperm-free TF with sperm preparations prod uced 17 alpha,20 beta-DP. The amount of 17 alpha,20 beta-DP production by intact TF or co-incubation of sperm-free TF with sperm preparation s accumulated with time, but the amount of 17 alpha-hydroxyprogesteron e declined. These results suggest a two-cell type model of the 17 alph a,20 beta-DP production in the testis. Testicular somatic cells produc e 17 alpha-hydroxyprogesterone in response to gonadotropin, then 17 al pha-hydroxyprogesterone is converted to 17 alpha,20 beta-DP by sperm 2 0 beta-hydroxysteroid dehydrogenase.