Blood pressure vulnerability to volume contraction: regulation by adrenal cortical hormones

Although the unique sensitivity of blood pressure to hemorrhage after adrenalectomy can be overcome by adrenocortical hormones the specificity of this steroid effect is not known. Under pentobarbital anesthesia five groups of six adult male Sprague-Dawley rats were bled into a 0.9% saline-primed pressure-balanced reservoir. A mean arterial pressure of 50 Torr was maintained for 3 h. When compared to normal rats, those with adrenalectomy showed significantly lowered bleeding volume (P less than 0.05 to less than 0.001). In untreated adrenalectomized rats 120 min following hemorrhage, saline was consistently taken up from the reservoir to maintain blood pressure at 50 Torr. Deoxycorticosterone-cortisol (intravenous bolus coupled with infusion) restored bleeding volume to normal in adrenalectomized rats. Aldosterone (constant infusion) also protected bleeding volume after adrenalectomy, P less than 0.05 to less than 0.01, but this effect was significantly less striking than that of cortisol 180 min after the onset of bleeding, P less than 0.001. Sham adrenalectomy did not affect bleeding volume. Aldosterone appears to be effective in restoring normal bleeding volume sensitivity after adrenalectomy but this effect of aldosterone is less sustained than that seen with cortisol.