Colchicine injected into the anterior forebrain in rats decreases blood pressure without changing the responses to haemorrhage.

In a previous publication rats were shown to develop a marked positive sodium balance 6 days after injection of 1 microgram colchicine into their anterior forebrains. This was thought to be the normal hydromineral balance response to correct an hypothesised colchicine-induced decrease in blood volume (and/or pressure). To test this hypothesis, fluid and sodium intakes and excretion were measured before and then for 6 days following injection of colchicine (1 microgram in 250 nl) into the anterior forebrain, around the diagonal band of Broca, in male Wistar rats. At the end of the 6 days the animals were anaesthetised with urethane and blood pressure measured continuously before during and after a 3.5 ml haemorrhage. Blood pressure was significantly reduced (86.4 +/- 3.9 n = 11 vs. 67.7 +/- 3.4 mm Hg n = 12, p < 0.01) in the colchicine-treated rats compared to the controls and failed to recover following the haemorrhage. Measured blood parameters were similar in both colchicine-treated and nontreated groups, including plasma levels of vasopressin both before and following the haemorrhage. These results suggest that the colchicine injections may have compromised a central component of the sympathetic nervous system, thereby leading to the significant decrease in blood pressure without compensatory vasopressin release, and the lack of recovery of the decrease in blood pressure following a haemorrhage.