br peptidic dual ETA ETB endothelin receptor antagonist bose
peptidic dual ETA/ETB endothelin A83 01 antagonist bosentan atte-nuated the tumor-induced heat hyperalgesia for one hour, starting within 30 min of treatment, at both doses tested (Fig. 2C, p < 0.05 versus sham rats treated with vehicle and p < 0.05 versus tumor-bearing rats treated with vehicle). Sham animals treated with vehicle or bosentan did not display any diﬀerence in response latencies at any time point (Fig. 2C, p > 0.05).
3.2. Eﬀects of local endothelin receptor blockade on tumor-induced increase in facial grooming
On day 6 post tumor cell inoculation, tumor-bearing rats displayed increased spontaneous grooming relative to sham controls (Fig. 3A, p < 0.01 versus sham rats treated with vehicle). Local administration of the control drugs, lidocaine or morphine blocked the increase in spontaneous grooming of tumor bearing rats to values equivalent to those shown by sham controls (Fig. 3A, p < 0.05 versus tumor-bearing
C.M. Kopruszinski et al.
rats treated with vehicle). Local administration of lidocaine or mor-phine to sham rats failed to alter grooming behavior (Fig. 3A, p > 0.05).
Fig. 2. Eﬀect of local administration of lidocaine, morphine and endothelin receptor antagonists on tumor-induced facial heat hyperalgesia. A. Local treatment with lidocaine and morphine reduced heat hyperalgesia in tumor-bearing rats on day 6 post inoculation by 30 min after administration (*p < 0.05 versus Sham-Vehicle and #p < 0.05 versus Tumor-Vehicle, n=5-8). B. Local administration of BQ-123 and BQ-788, either alone or in combi-nation, failed to modify tumor-induced heat hyperalgesia (*p < 0.05 versus Sham-Vehicle, n=6-10). C. Local treatment with bosentan, at both doses, re-duced heat hyperalgesia in tumor-bearing rats by 30 min post administration (*p < 0.05 versus Sham-Vehicle and #p < 0.05 versus Tumor-Vehicle, n=6-12). Results are presented as mean ± S.E.M. and statistical analysis was as-sessed by two-way ANOVA followed by Tukey test.
modify the tumor-induced increase in grooming behavior when tested at the lower dose of 10 μg (Fig. 3C, p > 0.05versus tumor-bearing rats treated with vehicle). Nonetheless, local bosentan treatment at the higher dose of 30 μg eﬀectively blocked tumor-induced increase in grooming, with the time spent grooming equivalent to that of sham controls (Fig. 3C, p < 0.001 versus tumor-bearing rats treated with vehicle and p > 0.05 versus sham rats treated with vehicle). Also, bosentan at 30 μg did not modify the grooming behavior of sham rats (Fig. 3C, p > 0.05versus sham rats treated with vehicle).
3.3. Local lidocaine, morphine and bosentan treatment failed to control ongoing nociception related to facial cancer
Local treatments with bosentan (30 μg/50 μl), lidocaine (1 mg/ 50 μl) or morphine (30 μg/50 μL) failed to induce CPP on the test day (i.e. day 6 after tumor cell inoculation), as evidenced by the absence of any significant alterations in the time spent in the pairing chambers following two conditioning sessions on days 4 and 5 after inoculation. Pre-conditioning (baseline) scores measured on day 3 after inoculation did not diﬀer between the vehicle-paired chamber and the drug-paired chamber. On the test day, local lidocaine, morphine and bosentan treatments did not increase time spent in the drug-paired chamber of tumor-bearing animals when compared to pre-conditioning scores measures (Table 1).
This study showed the ability of peripheral blockade of both ETA and ETB endothelin receptors in controlling the facial heat hyperalgesia and increased facial grooming behavior in a model of facial cancer in rats. On the other hand, the current data demonstrate that peripheral dual blockade of both ETA and ETB receptors failed to modify tumor-induced ongoing facial nociception. These data suggest that peripheral ETA and ETB receptors mediate responses related to evoked nociception and increased grooming induced by facial cancer.
We recently demonstrated that systemic treatment with the dual endothelin ETA and ETB receptor antagonist bosentan abolished tumor-induced heat hyperalgesia, increased spontaneous grooming and on-going nociception in the same facial cancer model used in the present study (Kopruszinski et al., 2018). However, the contribution of per-ipheral endothelins was not investigated. Herein, it was shown that local treatment with bosentan blocked facial heat hyperalgesia and increased facial grooming in tumor-bearing rats. This eﬀectiveness was similar to that promoted by local treatment with morphine and lido-caine, used as control drugs in this study. On the other hand, local treatments with the peptidic endothelin receptors antagonists BQ-123 and BQ-788, alone or in association, were unable to reduce the facial heat hyperalgesia or increased facial grooming of tumor-bearing rats. This ineﬀectiveness might be a result of increased synthesis and release of proteases by the tumor cells, resulting in the hydrolysis, and conse-quently, the degradation of the BQ molecules prior to receptor binding (Hardt, Lam, Dolan, & Schmidt, 2011; Schmidt, 2014). Thus, these data suggest that local both receptors contribute to the development of facial