Gonadotropic hormone (GtH) receptors in the testis of the troutSalmo gairdneri: in vitro studies

A particulate fraction obtained from trout testis at the time of spermiation shows saturable binding sites for¹²⁵I-labeled salmon gonadotropin (¹²⁵I-GtH). Non-gonadal tissues (liver, muscle and spleen) did not demonstrate specific¹²⁵I-GtH binding. The tracer's specific activity was determined by the self-displacement method (18 to 30 Ci/g). Maximal specific binding ability of¹²⁵I-GtH varied from 20 to 30% of the labelled ligand added, depending on the hormone preparation. Specific binding of¹²⁵I-GtH to 20 mg of the testis membrane varied from 40 to 85% of the total binding depending on the method of membrane prepratation, and was competitively inhibited by concentrations of unlabelled GtH ranging from ca 1 to 1000 ng/ml of incubate. Gonadotropin of mammalian origin, ovine TSH or salmon prolactin competed only weakly, or not at all, for testicular gonadotropin binding sites (relative potencies s-GtH>>FSH=hCG>s-PRL>bTSH). Scatchard analysis of equilibrium binding studies shows that saturable gonadotropin binding was due to a class of high affinity binding sites (sites I Ka3×10¹⁰ M^–1) and possibly to a second class of lower affinity binding sites (sites II Ka=5 to 14×10⁸ M^–1). The binding capacity of sites I, as measured in enriched membrane preparations, was 45±18 fmoles/g of testis during the period of spermiation. The concentration of GtH required to obtain half maximal displacement of¹²⁵I-GtH in the binding studies was of the same order of magnitude as the apparent ED50 for GtH stimulation of 11-Cetotestosterone (11KT) secretion by trout testesin vitro. Mammalian LH and FSH were 100 to 1000 folds less potent than salmor GtH to increase 11 KT secretion.     

Explaining host–parasitoid interactions at the landscape scale: a new approach for calibration and sensitivity analysis of complex spatio-temporal models

Landscape Ecology - Linking spatial pattern and process is a difficult task in landscape ecology because spatial patterns of populations result from complex factors such as individual traits, the...