Hemodynamic responses elicited by systemic injections of isotonic and hypertonic saline in hemorrhaged rats

•Controlled hemorrhage (HEM) decreased mean arterial blood pressure (MAP) in rats.•The fall in MAP was associated with a pronounced vasodilation in the hindquarter bed.•Subsequent injection of isotonic saline did not fully normalize MAP.•Hypertonic saline produced dramatic initial responses and normalized MAP.

PurposeThe objectives of this study were (i) to characterize the hemodynamic responses caused by controlled hemorrhage (HEM) in pentobarbital-anesthetized rats, and (ii) to determine the responses elicited by systemic bolus injections of isotonic saline (0.15 M) or hypertonic saline (3 M) given 5 min after completion of HEM.ResultsControlled HEM (4.3 ± 0.2 ml/rat at 1.5 ml/min) resulted in a pronounced and sustained fall in mean arterial blood pressure (MAP) to about 40 mm Hg. The fall in MAP was associated with a reduction in hindquarter vascular resistance (HQR) but no changes in renal (RR) or mesenteric (MR) vascular resistances. Systemic injections of isotonic saline (96–212 μmol/kg i.v., in 250–550 μl) did not produce immediate responses but promoted the recovery of MAP to levels below pre-HEM values. Systemic injections of hypertonic saline (750–3000 μmol/kg, i.v., in 250–550 μl) produced immediate and pronounced falls in MAP, RR, MR and especially HQR of 30–120 s in duration. However, hypertonic saline prompted a full recovery of MAP, HQR and RR to pre-HEM levels and an increase in MR to levels above pre-HEM values.ConclusionsThis study demonstrates that (i) HEM induced a pronounced fall in MAP which likely involved a fall in cardiac output and HQR, (ii) isotonic saline did not fully normalize MAP, and (iii) hypertonic saline produced dramatic initial responses, and promoted normalization of MAP probably by restoring blood volume and cardiac output through sequestration of fluid from intracellular compartments.