Cardiovascular Effects of Catecholamines Injected into the DBB of Rats, Influence of Urethane Anaesthesia and Local Colchicine

In a previous publication it was shown that 1 microgram colchicine injected into the diagonal band of Broca (DBB) produced a significant decrease in femoral artery blood pressure (and/or volume) measured in urethane-anaesthetised rats. In order to test if the central catecholamines were involved in this effect, guide cannulae were implanted in the DBB and a catheter in the femoral artery. On-line pressure recordings were taken before during and after alpha1, alpha2 and beta adrenoreceptor agonists and antagonists were injected into the region of the DBB of non-anaesthetised and urethane anaesthetised male Wistar rats with and without injection of colchicine. Arterial pressure was significantly increased in the non-anaesthetised rats (114.6+/-2.6 n=11 vs. 149.3+/-3.3 mmHg n=12, p<0.01) yet significantly reduced (82.0+/-3.9 n=11 vs. 63.8+/-4.5 mmHg n=12, p<0.01) in the urethane treated rats by the alpha2 agonist clonidine. The alpha2 antagonist yohimbine blocked these effects in both preparations. In contrast, the beta adrenoreceptor agonist isoprenaline produced a significant decrease in arterial pressure in both preparations (107.7+/-3.9 n=11 vs. 85.9+/-4.0 mmHg n=12, p<0.01) (102.6+/-6.7 n=11 vs. 81.7+/-3.4 mmHg n=12, p<0.01) and this effect was blocked by the beta antagonist propranolol. Colchicine injected into the DBB abolished the effects of the alpha2 agonist and antagonist in the non-anaesthetised but not the anaesthetised rats. The responses to the beta agonist and antagonist were not greatly affected by the colchicine in the non-anaesthetised rats whereas in the anaesthetised rat beta agonist injection tended to totally depress arterial pressure. These results suggest that the sympathetic nervous system in the DBB plays a significant role in the central control of arterial pressure and that the alpha2 component is significantly affected by the state of anaesthesia.