A method that allows measurement of GH-R in individual testes at all stages of spermatogenesis was validated. Crude testicular preparations were chosen because they gave a less variable and a higher-recovery yield of receptors than protocols using enriched membrane preparations. In this latter protocol, dramatic changes in testis composition during the reproductive cycle influence the yield of membrane recovery and create technical variability between stages (data not shown). flovent inhaler
Furthermore, GH-R is localized in membranes associated with intracellular structures as well as plasma membranes of GH target cells in mammals and teleost fish , and a crude membrane preparation could be more representative of the potential of tissue receptivity to GH than enriched plasma membrane preparations. Finally, this method allows the quantification of GH-R on small amounts of tissue, and therefore on individual gonads at all stages of spermatogenesis. Desaturation by MgCl2 treatment of the binding sites possibly occupied by endogenous GH could not be applied to crude testis preparation. Nevertheless, the low levels of plasma GH found at all stages of spermatogenesis suggest that the number of free binding sites estimated in this study was a good assessment of total binding sites.