Pre- and postsynaptic effects of brimonidine on isolated rabbit iris dilator muscles

Sonoko Tatsui,1 Hitoshi Ishikawa,2 Kimiya Shimizu,1 Kimiyo Mashimo1 1Department of Ophthalmology, School of Medicine, Kitasato University, 2Department of Orthoptics and Visual Sciences, School of Allied Health Sciences, Kitasato University, Sagamihara, Japan Purpose: Brimonidine is an imidazoline compound used for the treatment of glaucoma, but having very little effect on pupil diameter. Like para-aminoclonidine, most imidazoline compounds interact with postsynaptic α-adrenoceptors and cause pupil dilatation. Therefore, as part of an investigation of the mechanism of action of brimonidine on pupil diameter, the present study was initiated to measure, in vitro, the relative potency of brimonidine on the pre- and postsynaptic α-adrenoceptors of rabbit iris dilator muscle. Methods: The contractile activity of brimonidine and its effect on twitch contraction evoked by electrical field stimulation were studied in isolated rabbit iris dilator muscles by isometric tension recording. Results: Brimonidine significantly inhibited the twitch contraction of the dilator muscle caused by field stimulation, without affecting the response to exogenously applied phenylephrine. Compared to phenylephrine, brimonidine caused only a small contractile response with % maximum contraction values of<10%. Conclusion: These results suggest that brimonidine may act on nerve endings to inhibit adrenergic neurotransmission with very little effect on postsynaptic α-adrenoceptors. This may indicate that brimonidine reduced the pupil diameter just a little, thus improving night vision. Keywords: brimonidine, rabbit iris dilator, electrical field stimulation, presynaptic α2-adrenoceptor, postsynaptic α1-adrenoceptor, imidazoli

Clinical profile of long-term survivors of breast or thyroid cancer with metastatic spinal tumours

Patients with breast or thyroid cancer with metastatic spinal tumours are expected to survive relatively longer than patients with other cancers with metastatic spinal tumours. The purpose of this study was to determine the clinical characteristics of long-term survivors of breast or thyroid cancer with metastatic spinal tumours. We studied the clinical profile of long-term survivors by comparing the characteristics of nine patients who had survived for at least 5 years after a spinal operation with the characteristics of 16 patients who had not. Our results showed that the longer the time from the diagnosis of the primary cancer to the spinal operation, the longer patients with breast or thyroid cancer and metastatic spinal tumours would survive. Six of the eight patients (75.0%) who had undergone the spinal operation at least 5 years after the diagnosis of the primary cancer survived especially long. In conclusion, the duration from the diagnosis of the primary cancer to the spinal operation is very useful for predicting a prognosis in patients with breast or thyroid cancer and metastatic spinal tumours

Clinical profile of long-term survivors of breast or thyroid cancer with metastatic spinal tumours

Patients with breast or thyroid cancer with metastatic spinal tumours are expected to survive relatively longer than patients with other cancers with metastatic spinal tumours. The purpose of this study was to determine the clinical characteristics of long-term survivors of breast or thyroid cancer with metastatic spinal tumours. We studied the clinical profile of long-term survivors by comparing the characteristics of nine patients who had survived for at least 5 years after a spinal operation with the characteristics of 16 patients who had not. Our results showed that the longer the time from the diagnosis of the primary cancer to the spinal operation, the longer patients with breast or thyroid cancer and metastatic spinal tumours would survive. Six of the eight patients (75.0%) who had undergone the spinal operation at least 5 years after the diagnosis of the primary cancer survived especially long. In conclusion, the duration from the diagnosis of the primary cancer to the spinal operation is very useful for predicting a prognosis in patients with breast or thyroid cancer and metastatic spinal tumours

Evaluation of DuraGen in preventing peridural fibrosis in rabbits

Peridural fibrosis is the scar tissue formed over the dura mater after a laminectomy. It has been implicated as a cause of persistence of pain after spinal surgery and associated with increased risk of complications during revision surgery. The application of a mechanical barrier to cover the peridural space to block the migration of inflammatory cells from superficial layers to the epidural space can potentially prevent or decrease scar formation. The authors evaluated the use of DuraGen for this purpose. Seventeen New Zealand White rabbits underwent bilateral L-4 and L-7 laminectomies. Each space was randomly assigned to either receive DuraGen, fat graft, or no (sham) treatment. At a mean 18 +/- 4 weeks after surgery, the animals underwent magnetic resonance (MR) imaging with and without Gd enhancement, and the area of the scar tissue overlying the middle of the laminectomy was measured. The rabbits were killed and the spinal cords with an intact dural covering were harvested. The midsection of each treated level was evaluated histologically and the scar area was measured. In rabbits in which a fat graft was placed, MR imaging of the epidural space demonstrated a significant (p < 0.05) increase in the mean area (0.9713 mm2) of scar tissue compared with those in which DuraGen was used (0.687 mm2) or those receiving sham treatment (0.6661 mm2). The same correlation was observed when the histological sections were measured at the middle of the laminectomy site where the mean areas of both DuraGen (1008 mm2) and control (2249 mm2) groups were significantly lower than that in the fat graft group (6007 mm2) (p < 0.01 and 0.05, respectively). No significant differences between the DuraGen and control groups were observed. The authors demonstrated that peridural scarring formed in all groups. The mean area of scar deposition was significantly higher in the fat graft group than in the DuraGen or control group both on MR imaging and histological analysis. DuraGen was more effective than a fat graft in preventing epidural fibrosis but not significantly different from that occurring in control animals