ABSTRACT
Albino rats were made hypertensive by 1 percent NaCl in the drinking water for 4-5 months, systolic (SBP) and distolic blood pressure (DBP) were 164.0 +/- 10.1 mm Hg and 118.7 +/- 4.6 mm Hg respectively, vs. control rats whose SBP and DBP were 119.0 +/- 4.4 mm Hg and 86.8 +/- 4.3 mm Hg respectively. Psychosocial stress (1 hour daily for 4-5 months) only raised SBP to 140.0 +/- 5.2 mm Hg; DBP remained unaltered. One percent NaCl intake combined with psychosocial stress, increased SBP and DBP but not significantly beyond the level observed with single 1 percent NaCl administration. Formerly described control and hypertensive rats were anesthetized with sodium pentobarbital (40 mg/kg) and stereotaxically injected into de cisterna magna (i.c.) with 20 microliters of 1.5 M NaCl solution. During i.c. injection, intraarterial SBP, DBP and heart rate (HR) were continuously recorded. After i.c., 1.5 M NaCl injection, mean arterial pressure (MAP) increased 21.0 +/- 4.0 mm Hg and HR 51.0 +/- 5.0 beats/min in control rats. Rats made hypertensive by 1 percent NaCl intake showed a significantly lower increase of MAP, 11.0 +/- 1.8 mm Hg; HR increased 37.0 +/- 4.3 beats/min. Rats submitted only to psychosocial stress displayed a response similar to the one described in control rats. Hypertensive rats submitted to both 1 percent NaCl intake and psychosocial stress had a more intense reduction of the hypertensive and tachycardic response, 8.0 +/- 2.2 mm Hg and 20.0 +/- 3.2 beats/min respectively. Control i.c. injection with the same volume of saline (0.15 M NaCl) did not change significantly SBP, DBP or HR in a separate group of rats. Left ventricle weight (0.754 +/- 0.0333 g) was augmented in the 1 percent NaCl treated group (0.795 +/- 0.038 g), and increased its protein content by 13.1 percent changes not statistically significant). The highest increase of the left ventricle weight (23.7 percent above control) with no change in its protein content was observed in rats submitted to 1 percent NaCl intake plus psychosocial stress. In conclusion, chronic high NaCl intake increased blood pressure; psychosocial stress acted as a weak stimulus for SBP and DBP increase, and central nervous system sodium chloride sensitivity for delivering a peripheral sympathetic discharge was found decreased in rats made hypertensive by a high salt intake