Effects of the androgenic/anabolic steroid stanozolol on GABAA receptor function: GABA-stimulated 36Cl- influx and [35S] TBPS binding.

We have recently demonstrated that androgenic/anabolic steroids modulate in vitro ligand binding to the benzodiazepine binding site(s) associated with the gamma-aminobutyric acidA (GABAA) receptor complex (Masonis and McCarthy, 1995). One androgenic/anabolic steroid in particular, stanozolol, appears to stabilize the GABAA receptor in a moderate-affinity state for benzodiazepine binding. In the present study, we demonstrate the effects of stanozolol on the functional responsiveness of the GABAA receptor. After pre-incubation with stanozolol, we observed a decrease in the Emax and EC50 values for GABA-stimulated 36Cl- influx into cortical synaptoneurosomes. Moreover, in the presence of stanozolol, flunitrazepam-enhanced GABA-stimulated 36Cl- influx was lost, and the GABAA receptor was stabilized in a functional state that was resistant to further desensitization by agonist. Stanozolol does not appear to reduce GABA-stimulated 36Cl- influx by acting as a channel blocker at the well-characterized channel blocker binding site, as illustrated by the GABA-sensitive biphasic effects of stanozolol on [35S] t-butylbicyclophosphorothionate binding. These results demonstrate a novel, nongenomic mechanism for androgenic/anabolic steroidal modulation of CNS function.

Direct interactions of androgenic/anabolic steroids with the peripheral benzodiazepine receptor in rat brain: implications for the psychological and physiological manifestations of androgenic/anabolic steroid abuse.

The peripheral benzodiazepine receptor (PBR) is a mitochondrial protein involved in regulating steroid synthesis and transport. We report here the effects of androgenic/anabolic steroids (AAS) on the binding of the PBR-specific ligand [3H] PK11195 to male rat brain cortical synaptoneurosomes. Two synthetic AAS, stanozolol and 17beta-testosterone cypionate (17beta-cyp), significantly inhibited 1 nM [3H] PK11195 binding at concentrations greater than 5 and 25 microM, respectively. Stanozolol was the most effective inhibitor, reducing [3H] PK11195 binding by up to 75%, compared to only 40% inhibition by 17beta-cyp, at 50 microM AAS concentration. Two other AAS, 17alpha-methyltestosterone and nortestosterone decanoate, were incapable of inhibiting [3H] PK11195 binding at concentrations up to 50 microM. On the basis of Scatchard/Rosenthal analysis, [3H] PK11195 binds to two classes of binding sites, and the inhibition of [3H] PK11195 binding by stanozolol appears to be allosteric, primarily reducing binding to the higher affinity [3H] PK11195 binding site. These results, in combination with earlier studies indicating the direct effects of AAS on the function of additional central nervous system receptor complexes, suggest that the behavioral and psychological effects of AAS result from the interactions of AAS with multiple regulatory systems in the brain.

Direct effects of the anabolic/androgenic steroids, stanozolol and 17 alpha-methyltestosterone, on benzodiazepine binding to the. gamma-aminobutyric acid(a) receptor.

Various exogenous and endogenous steroids have been demonstrated to have both enhancing and inhibiting effects on ligand binding to the gamma-aminobutyric acid(A) receptor (GABAA receptor) in previous studies. In the present study we have explored the possibility that an additional class of synthetic steroidal compounds, anabolic/androgenic steroids (AAS), mediate some of their CNS effects through direct interaction with the GABAa receptor. At micromolar concentrations, two AAS, stanozolol and 17 alpha-methyltestosterone (17 alpha-MT), significantly inhibited 1 nM [3H]flunitrazepam ([3H]Fln) binding to rat brain cerebrocortical membranes. Inhibition of 1 nM [3H]Fln binding by stanozolol was similar for both males and females (approximately 50% inhibition at 50 microM stanozolol). 17 alpha-MT was much less efficacious, but did significantly inhibit 1 nM [3H]Fln binding at concentrations > 10 microM. In equilibrium binding assays, stanozolol (50 microM) raised the apparent KD for [3H]Fln binding. The observed changes in the [3H]Fln binding curve, when analyzed by Rosenthal analysis, reveal complex equilibrium binding behavior. In females, the Rosenthal plot was best fit by a two site binding model. Stanozolol (50 microM) inhibited binding to the higher affinity site in a manner consistent with competitive inhibition, increasing the KD without changing the BMAX. However, the effect of stanozolol on the binding to the low affinity site was more complex, with an increase in the the KD and the BMAX. In males the data were best fit by a single binding site model. This single site exhibited a slight increase in the KD and a decrease in the BMAX in the presence of 50 microM stanozolol.(ABSTRACT TRUNCATED AT 250 WORDS)