Changes in regional brain synaptosomal high affinity choline uptake during the development of hypertension in spontaneously hypertensive rats.

The high-affinity uptake of choline (HAChU) by freshly prepared crude synaptosomal fractions was employed as relative measure of regional brain cholinergic activity. The Vmax for uptake as determined by the accumulation of a tracer amount of 3H-choline in the presence of unlabeled choline (0.2-2 microM) varied 6 fold depending upon the region examined (stratum greater than hypothalamus greater than medulla-pons). HAChU was hemicholinium-3-sensitive and linear at 37 degrees C from 1 to 8 min in all brain regions. Respective brain synaptosomal fractions derived from adult (12 week old) spontaneously hypertensive (SH) rats and normotensive Wistar Kyoto (WK) rats revealed no difference in the Vmax for HAChU from synaptosomes derived from the striatum of either strain. However, there was a significant increase in the Vmax for HAChU measured from the medulla-pons of SH rats compared with WK rats. In older (22 weeks) rats, the Vmax for HAChU was 78% greater than age-matched WK control rats. In addition, a highly significant correlation was found between resting systolic blood pressure and the Vmax for HAChU both in the medulla-pons (r = 0.76) and hypothalamus (r = 0.48). That the increase in HAChU in SH rats was not a consequence of elevated pressure, was indicated by the lack of effect of prolonged i.v. infusion of pressor agents in normotensive rats on HAChU. These findings are consistent with a role for brain cholinergic neurons in the maintenance of hypertension in SH rats.