Sex-dependent effect of a dorsal septal lesion on the blood pressure of laboratory rats.

The role of the septum in the regulation of blood pressure was studied in adult female and male laboratory (Alderley Park strain of Wistar) rats allowed a free choice between water and a 0.9% or 3% NaCl solution or simply given water. A lesion was formed in the dorsal septum and 30-66 days afterwards the mean arterial pressure was measured in the unanaesthetized animals' tail. In females the blood pressure was not affected either by the lesion itself, or by the lesion combined with a raised NaCl intake. In males, combination of the lesion with a raised salt intake was accompanied by elevation of the blood pressure, which attained values considered to be hypertensive (over 20 kPa). The increase occurred after 9 days' free choice between water and 3% NaCl solution preceded by 14 days' free choice between water and saline. At the same time, the computed NaCl concentration in the total fluids intake was higher in the control and septal females than in the control and septal males for both the salt regimens. Three days after changing from a free choice regimen to plain water intake, the blood pressure of septal males had fallen to normal values. After a protracted water regimen (43 days after discontinuing free choice), these animals had a lower blood pressure than sham-operated males after the same interval. The determinant variable in the effect of a dorsal septal lesion on the blood pressure in the presence of a hypertensogenic stimulus (NaCl) was the sex of the experimental animals.