Pheromone reception in salmonid fish: identification and characterization of putative steroid receptors in olfactory tissue of brown and rainbow trout

Pottinger, T.G.. 1996 Pheromone reception in salmonid fish: identification and characterization of putative steroid receptors in olfactory tissue of brown and rainbow trout. NERC, Institute of Freshwater Ecology, 54pp. (IFE Project no: T11050) (Unpublished)

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Specific binding sites for testosterone have been detected in three compartments of olfactory tissue from brown and rainbow trout. Binding of 3H-testosterone to the membrane fraction of olfactory tissue is of high affinity (Kd = 0.5 - 1.9 nM) and limited capacity (Nmax= 30 - 60 fmol mg-1 protein). Binding is reversible, and is eliminated by protease treatment. The binding site exhibits a high degree of ligand specificity, 11β-hydroxytestosterone, 11-ketotestosterone, 17α-hydroxyprogesterone, 17α, 20β-dihydroxy-4-pregnen-3-one, cortisol, and estradiol-17β all fail to displace testosterone at 20-fold excess. These attributes are characteristic of specific steroid receptor proteins. Binding of testosterone within the cytosol fraction is of moderate affinity (Kd = 9.0 - 23.0 nM) and high capacity (Nmax = 0.5 - 2.9 pmol mg-1 protein) and binding of testosterone is more readily displaced by a number of steroid competitors than is the case for the membrane site. The rate of association and dissociation of testosterone from the cytosolic binding site is markedly more rapid than the equivalent processes in the membrane fraction. Binding of testosterone to the nuclear extract is of high affinity (Kd ~ 3.0 nM) and limited capacity (Nmax ~ 50 fmol mg-1 protein). There are no marked differences between species or between sexes in the affinity or capacity of testosterone-binding sites in nuclear extract or membrane fraction. However, cytosolic testosterone-binding sites are three- to four-fold more abundant in rainbow trout than in brown trout, and female rainbow trout have more cytosolic binding sites than male rainbow trout, but a lower affinity for testosterone than male sites. Preliminary evidence supports the involvement of the membrane-associated testosterone-binding site in olfactory processes. Rainbow trout display an EOG response to testosterone at a concentration (10-9 M) which is consistent with the equilibrium dissociation constant (Kd) of the membrane-associated testosterone-binding site. The concentration of ligand at which half the binding sites are saturated (Kd) is in the range 0.5 - 2.0 . 10-9 M for membrane-associated testosterone binding. Binding of 3H-testosterone to the membrane-associated site shows a pH dependency which is comparable to the effects of pH on the EOG response to testosterone in intact fish. The data concerning the attributes of the membrane associated testosterone-binding site are consistent with the olfactory tissue of salmonids possessing the capability to respond to testosterone present in the aquatic environment. The intracellular testosterone-binding sites show characteristics common to testosterone receptors in other fish tissues which are known androgen target tissues. This suggests that the development and/or function of salmonid olfactory tissue may be open to influence by endogenous testosterone. This is the first report of androgen binding to olfactory tissue in fish, and the first report of a membrane-associated androgen binding site in fish.

Item Type: Publication - Report
UKCEH and CEH Sections/Science Areas: _ Pre-2000 sections
Funders/Sponsors: Ministry of Agriculture, Fisheries and Food
Additional Keywords: pheromone, rainbow trout, brown trout, steroid, testosterone, receptor, olfactory tissue, olfaction
NORA Subject Terms: Zoology
Biology and Microbiology
Date made live: 28 Jul 2015 10:20 +0 (UTC)

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