Dietary calcium is known to prevent salt-induced hypertension, although
the exact mechanism responsible for this remains unknown. One of the
proposed mechanisms of the pathogenesis of salt-induced hypertension is
the impairment of baroreflex sensitivity. Hence we investigated the
effect of calcium supplement on baroreceptor in salt-loaded rats. The
experiment was performed in male sprague-Dawley rats fed with measured
salt and/or calcium diets and given tap water ad libitum for 6 weeks.
Blood pressure and heart rate measurments were done in anaesthetised
animals through direct invesive method using Grass Polygraph. Bilateral
carotid occlusion test was used to determine the baroreflex sensitivity
in the rats. There was increase in mean arterial pressure (MAP) of
salt-loaded rats relative to control (132.6 ± 2.3 vs. 90.1 ±
1.5mmHg; n=8; P<0.05), while dietary calcium alone did not have any
significant effect on the MAP (84.5 ± 1.7mmHg; n=8). During the
feeding period, the salt consumed by salt-loaded rats was significantly
higher than those of control but lower than that of salt-loaded-fed
rats. Also, water intake was highest in salt-loaded rats compared with
other experimental rats. However, the volume of urinary excretion was
higher in salt-loaded-calcium-fed rats than salt-loaded rats but both
were higher than control. These resulted in attenuated baroreflex
sensitivity of salt-loaded rats relative to control (0.55 ± 0.2
vs. 1.25± 0.1 beats/mmHg, n=7; P<0.05). However, dietary
calcium enhanced baroreflex sensitivity in salt-loaded-fed rats (2.21
± 0.2 beats/min/mmHg, n=7; P<0.05) compared with control and
salt-loaded rats. The study shows that salt-loading led to hypertension
probably through alteration of haemodynamic function and impairment of
baroreflex sensitivity. Calcium supplement prevention of salt-induced
hypertension seems to reverse these, thus resulting in maintenance of
water balance and baroreceptor integrity