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 mu g colchicine injected into the diagonal band of Broca (DBB) produced a significant decrease in femora l 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 femo ral artery. On-line pressure recordings were taken before during and after alpha 1, alpha 2 and beta adrenoreceptor agonists and antagonists were inje cted into the region of the DBB of non-anaesthetised and urethane anaesthet ised male Wistar rats with and without injection of colchicine. Arterial pr essure 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 redu ced (82.0 +/- 3.9 n = 11 vs. 63.8 +/- 4.5 mmHg n = 12, p < 0.01) in the ure thane treated rats by the alpha 2 agonist clonidine. The alpha 2 antagonist yohimbine blocked these effects in both preparations. In contrast, the bet a adrenoreceptor agonist isoprenaline produced a significant decrease in ar terial 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 alpha 2 agoni st 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 anaesthetise d rat beta agonist injection tended to totally depress arterial pressure. T hese results suggest that the sympathetic nervous system in the DBB plays a significant role in the central control of arterial pressure and that the alpha 2 component is significantly affected by the state of anaesthesia. (C ) 1999 Elsevier Science B.V. All rights reserved.