To evaluate gender differences in salt-induced hypertension, female and male Dahl salt-sensitive rats were fed high (8.0% NaCl, HS) and low (0.3% NaCl, LS) salt diets. During a 3-week treatment period, blood pressure was significantly elevated in both female and male HS groups compared to their respective LS groups. The blood pressure and 4 week mortality rate of the female HS group, however, were significantly lower than those of the male HS group. Renal and aortic blood flows were reduced in male rats on HS diet compared to the LS group, while, in females, renal blood flow was elevated and aortic flow was maintained while on HS diet. Plasma prostaglandin E2 and prostacyclin levels were higher in females than males and unaffected by diet. In contrast, plasma nitric oxide levels were reduced by HS, regardless of gender. In isolated aortic rings, HS diet caused a smaller elevation in the stimulated norepinephrine release ratio in female rats than in males. Thus, salt-induced hypertension is associated with a reduction in levels of nitric oxide regardless of gender. Plasma prostaglandin E2 and prostacyclin levels were higher in females. Taken together, the higher plasma prostaglandin levels and reduced sympathetic activity in females may be contributing factors in their lower blood pressure and reduced mortality.

Microgravity is known to induce orthostatic intolerance and baroreflex impairment in astronauts. Cardiovascular responses observed in 30 degrees head-down tilt rat models, whether 24 hr whole body suspension (WBS) or 7 day tail-suspension (TS), mimic observations made during exposure to microgravity. We evaluated the cardiovascular effects of simulated microgravity and the subsequent post-suspension in rats using the above models. Mean arterial pressure (MAP) of both WBS and TS rats did not change during suspension. In both models, MAP decreased post-suspension and this response lasted for 6 hrs. Salt-loaded animals did not show a post-suspension reduction in MAP. Plasma ionized calcium was decreased at 2 hr of WBS, with no change in sodium, potassium, magnesium, glucose, or hematocrit. Body weight changes were similar for all animals whether under suspension or control conditions. Both rat models demonstrate post-suspension hypotension and these results support the notion that salt-loading may have some beneficial effects in ameliorating this hypotension.