β₂‐adrenergic control of plasma volume in hemorrhage

Abstract

Hemorrhage is associated with absorption of extravascular fluid from skeletal muscle to blood in order to compensate for the loss of intravascular volume. Our previous studies have shown that this fluid gain is mainly linked to beta-adrenergic microvascular adjustments leading to decrease in capillary hydrostatic pressure and to precapillary 'sphincter' mediated increase in the capillary surface area available for fluid exchange. In the present study the importance of beta-adrenergic control of plasma volume in bleeding was confirmed by measurement of changes in plasma volume after graded hemorrhage in animals with intact and blocked vascular beta 2-adrenoceptors (i.v. administration of the 'selective' beta 2-blocking agent ICI 118, 551). With intact beta 2-adrenoceptors plasma volume was gradually restored after bleeding so that about 50% of the shed plasma volume (about 35% of the shed blood volume) had been compensated for at two hours after exsanguination of 20% as well as 40% of the blood volume. The corresponding figures in animals with blocked beta 2-adrenoceptors were only 14% of the shed plasma volume and 8% of the shed blood volume at both degrees of hemorrhage.

Plasma volume expansion and transcapillary fluid exchange in skeletal muscle of albumin, dextran, gelatin, hydroxyethyl starch, and saline after trauma in the cat*

“…Plasma volume in these cats was 35.6.0 Ϯ 2.4 mL/kg. These values are in agreement with normal plasma volumes of 34 -37 mL/kg for the adult cat (35), confirming the reliability of the technique used for plasma volume measurement. Hemoglobin concentration was 125-135 g/L, sodium concentration 146 -148 mmoL/L, and pH 7.32-7.36, which are normal values for cats.…”

“…The plasma volume decreased during the surgical preparation of the skeletal muscle from normal values of 34 -37 mL/kg (35) to about 21 mL/kg, indicating severe hypovolemia; this was also supported by the high hemoglobin concentrations in the range of 155-165 g/L (Table 1) (compared with the normal values of 125-140 g/L for cats) and by the high vascular resistance in the muscle of 24 -30 PRU (compared with the normal values of 13-16 PRU) (32,33). The low pH values of 7.22-7.24 (Table 1) after the preparation (compared with normal pH values of 7.32-7.36 for anesthetized cats) also indicated disturbed perfusion, which was most likely an effect of activation of the baroreceptor reflex following hypovolemia.…”

Endogenous nitric oxide as a physiological regulator of vascular tone in cat skeletal muscle during haemorrhage

“…In another series of experiments the animals were subjected to graded acute haemorrhage, a large blood loss (35 %) and a moderate one (17.5 %) ; the blood loss was accomplished within " 1 min by arterial exsanguination, normal cat blood volume taken to be 50 mL kg −" body wt (for refs. see Hillman et al 1982). When the haemorrhage-induced vasoconstrictor response in the muscle preparation after 10-12 min had reached a well maintained steady state, -NAME in an effective dose for NOS blockade (see below) was infused close-arterially to the muscle region.…”

Influences on central hemodynamics in hemorrhage of β2‐adrenergic vascular control mechanisms

“…2 for the animals with intact Pz-adrenoceptors 2 h after exsanguination of 20 mlxkg-' are compared with corresponding ones observed in an additional series of /&blocked cats that were bled only 10 mlxkg-'. The reason for this comparison was the finding that the blood volume in the latter animals 2 h after bleeding (39 mlxkg-') was similar to that demonstrated for the 'intact' cats exposed to twice as large a bleeding (37 mlx kg-'; for details see Hillman et al 1982). Fig.…”