Evolution of Testicular GH-R during Spermatogenesis
Saturation experiments were conducted at the 8 stages of the spermatogenetic cycle (1-4 experiments per stage) on pools of gonads at the same histological stage (Table 1). Scatchard plots revealed that affinity constants were in the same order of magnitude (covariance analysis) during the entire spermatogenetic cycle, with a mean value at 4.5 X 109 ± 0.25 M 1 (n = 21), while binding capacities (Bmax) showed significant changes.
Since the equilibrium association constants at all stages of spermatogenesis were found to be similar, binding studies with only one-half saturating concentration of 125I-rtGH were used in order to allow work with small amounts of tissue and estimation of changes in GH-R in a large number of individual testes. Using this method, 125I-rtGH binding was measured on 41 individual gonads at different stages except for the immature stage; in this stage, pools of gonads were necessary to allow detection of sufficient binding (Fig. 4a). Binding decreased regularly from the beginning of spermatogenesis (stage II, spermatogonia proliferation: 706 fmol/g testis) to stage VII (mainly spermatozoa: 158 fmol/g testis), with a slight nonsignificant increase in the fully mature gonad (only spermatozoa: 217 fmol/g testis). buy flovent inhaler
TABLE 1. Ka and Bmax values for 125l-rtGH binding in testis and liver during spermatogenesis in rainbow trout. Pools of testes at the same spermatogenetic stage (stage l-ll: pools of 11 to 17 pairs of gonads; stage III—VIII: pools of 3 to 6 pairs of gonads) and livers corresponding to the same animals were used (mean ± SEM).
FIG. 4. Changes in GH-R concentrations in rainbow trout testis (a) and liver (b) during spermatogenesis. [,25l]rtGH-specific binding studies (120 000 cpm/tube) were performed with 20 mg of pellet per tube for testis and with 5 mg of pellet per tube for liver. Specific [125l]rtGH binding was measured on individual gonads chosen at each stage of spermatogenesis (except for stage I, where 5 pools of 2-8 pairs of gonads were used) and on the corresponding individual livers. Number of experiments are shown in parentheses above histograms. Results are expressed as the mean + SEM. “”“Indicates significant differences (p < 0.01).