A high level of low-affinity binding was found in a population consisting of a mixture of germ cells and various fibroblastic and somatic aggregated cells. Saturable binding with a high affinity (Ka = 3.8 X 109 M ‘) for 125I-rtGH was detected only in a fraction of testicular cells enriched in Sertoli cells after 4 days of culture. Similar results were obtained in two independent experiments.
Evolution of Hepatic GH-R and Plasma GH during Sperma togenesis
The characteristics of 125I-rtGH binding to crude hepatic preparations obtained from rainbow trout at different stages were also determined (Table 1). Scatchard plot analyses of the data indicate the presence of a single population of binding sites with unchanged high affinity (5.1 X 109 ± 0.06 M ‘, n = 16) for 125I-rtGH during the entire spermatogenetic cycle, and modest variations of binding capacity. Specific 125I-rtGH binding to individual livers corresponding to the testes studied was measured in single-point binding studies (Fig. 4b). Our results revealed that GH-R concentration showed little change over the spermatogenetic cycle. Binding was slightly higher in the early stages (6.5-6.7 pmol/g liver) than in the following stages of mei-osis and spermiogenesis, decreased significantly (p < 0.05) in stage VI (3.5 pmol/g liver), and then increased at the final stages (7.2 pmol/g liver). The GH-R concentration in liver appeared to be 6- to 30-fold higher than the GH-R concentration in testis when expressed in fmol/g tissue. The total binding capacity of the liver, expressed in fmol/liver per gram body weight (corrected for body growth), showed changes similar to those in the hepatic GH-R concentration (data not shown). buy asthma inhaler
The plasma levels of GH were low throughout spermatogenesis (0.7 ± 0.09 ng/ml) and tended to rise (nonsignificant) at the very end of the reproductive cycle in sper-miating fish (stage VIII). The relationships among plasma GH, GH binding in liver, and GH binding in testis were assessed by linear regression analysis of individual values. No significant correlation was found between these parameters (testicular GH-R concentration/hepatic GH-R concentration: r = —0.1; testicular GH-R concentration/plasma GH concentration: r = —0.04; hepatic GH-R concentration/ plasma GH concentration: r = -0.1).