GROWTH-HORMONE RECEPTORS IN TESTIS AND LIVER DURING THE SPERMATOGENETIC CYCLE IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

Changes in growth hormone (GH) receptivity in the testis during the re productive cycle were studied in rainbow trout (Oncorhynchus mykiss). This necessitated setting up a method to characterize GH receptors (CH -R) in crude testis homogenate. Binding of radiolabeled recombinant ra inbow trout GH (I-125-rtGH) to crude testis preparation was dependent on testicular tissue concentration. The sites were specific to GH, wit h no affinity for prolactins, gonadotropins, or insulin. Similar high affinities for I-125-rtGH were obtained with crude testis (4.5 x 10(9) +/- 0.25 M-1) and crude liver preparations (5.1 x 10(9) +/- 0.06 M-1) at all stages of spermatogenesis, as well as with testicular membrane preparations (2.4 x 10(9) M-1). CH-R concentration in testis was high during the immature stage (590 fmol/g testis); it then decreased regu larly from the beginning (stage II, spermatogonia proliferation: 706 f mol/g testis) to the end of spermatogenesis (stage VII: 158 fmol/g tes tis). Conversely, the absolute testicular capacity increased dramatica lly between stages IV and VI (1.2-16.2 pmol/2 gonads), when testicular growth is extremely rapid. GH-R concentration in the liver was highes t in early stages (6.5-6.7 pmol/g liver); this value then significantl y decreased during midspermatogenesis (stage VI: 3.5 pmol/g liver) and returned to immature levels at the end of the cycle. No significant c orrelation was found between GH-R in testis, CH-R in liver, and plasma CH concentration. Preliminary experiments performed on isolated popul ations of testicular cells revealed that binding of I-125-rtGH was det ectable in Sertoli cell-enriched fractions but not in germ cell popula tions. We conclude that GH-R are present in the testis during the enti re reproductive cycle in rainbow trout, probably in somatic cells and in particular in Sertoli cells.