Figure 7.
Effects of androgens on M1 concentrations in CSF and plasma in rats following tramadol administration (40 mg·kg−1, i.p.). Exogenous testosterone administration decreased the M1 concentration in CSF (A) and the relative extent of conversion of tramadol to M1 (G). Orchiectomy increased the M1 concentration in CSF (B) and the relative extent of conversion of tramadol to M1, and this was attenuated by testosterone supplementation. Propranolol pretreatment (20 μg, i.c.v.) reduced the orchiectomy-induced increase in CSF M1 concentration (C) and the relative extent of conversion of tramadol to M1. There was no change in M1 concentration in plasma from exogenous testosterone administration (D), orchiectomy (E) or orchiectomy with propranolol co-treatment (F); meanwhile, the relative extent of conversion of tramadol to M1 (H) was unchanged. ORC: orchiectomy. n = 5 per group, **P < 0.01, ***P < 0.001; significantly different from the respective controls.