When the results were expressed in fmol/mg of protein, the binding tended to change similarly (significant decrease from the beginning of spermatogenesis [190 fmol/mg of protein] to stage VII [70 fmol/mg of protein], and a nonsignificant increase [120 fmol/mg of protein] at stage VIII). However, the decrease was less pronounced because 1 g of mature testis tissue provided less protein than 1 g of immature testis tissue. These results are in good agreement with the data obtained in the saturation experiments (Table 1). The absolute binding capacity of the whole gonad (Fig. 5) expressed in pmol/2 gonads (or in pmol/2 gonads per gram body weight, i.e., corrected by body growth; data not shown) was very low in the smallest testes and was increased dramatically between stages IV and VI (1.2-16.2 pmol/2 gonads), when testicular growth was extremely rapid. buy asthma inhalers
GH Binding to Isolated Testicular Cells
In an attempt to identify GH target cells in the testis, saturation experiments were performed on various populations of isolated testicular cells (Fig. 6). In populations of round germ cells, hardly any specific binding could be observed either immediately after the dissociation procedure (data not shown) or after 4 days of culture (Fig. 6). Specific binding of 125I-rtGH was not detectable in the spermatozoa population (2 X 106 and 16 X 106 cells per tube, data not shown).
FIG. 5. Changes of GH-R capacities in rainbow trout testis during spermatogenesis. [125l]rtGH-specific binding studies (120 000 cpm/tube) were performed with 20 mg of pellet per tube at all stages of spermatogenesis. Number of experiments is shown in parentheses above histograms. Results are expressed as the mean + SEM. “Indicates significant differences (p < 0.01).
FIG. 6. Scatchard plots of [125l]rtGH-specific binding (50 000 to 1 000 000 cpm/tube) to testicular cell preparations (2 000 000 cells per tube). Scatchard plot analysis were performed with values for free (U) hormone corrected for MBA of the tracer.