Effects of haemorrhage on the distribution of the peripheral blood flow in the rabbit

Abstract

SUMMARY1. The effects of bleeding unanaesthetized rabbits by 26% of their blood volume on the blood flow in the portal, renal, muscle and skin beds were investigated in normal animals, in animals without functioning autonomic effectors, and in animals with section of the carotid sinus and aortic nerves.2. In animals without functioning autonomic effectors there was progressive vasodilatation during the 4 hr following haemorrhage, which differed markedly in the different regional beds studied. The dilatation was greatest in the portal bed, followed by kidney and skin, but there was no significant change in the vascular resistance in muscle.3. In normal animals with intact reflexes the vascular resistance either increases or remains at control values, suggesting that reflex constrictor effects oppose locally acting dilator mechanisms. During the 4 hr following haemorrhage reflex vasoconstrictor effects were greatest in kidney, followed by muscle, portal bed and skin.4. In animals with section of the carotid sinus and aortic nerves reflex constrictor effects were absent in the portal, muscle and skin beds, but significant vasoconstriction was still evident in the renal bed, though of smaller magnitude than in normal animals. The results suggest that the arterial baroreceptors are a major source of reflex activity following haemorrhage, but that other reflexogenic zones contribute to the renal effects in normal animals.

The role of cardiac receptor and arterial baroreceptor reflexes in control of the circulation during acute change of blood volume in the conscious rabbit.

“…There is good evidence that, in anesthetized animals, the output of cardiopulmonary receptor reflexes is not directed uniformly among the various vascular beds, but influences predominantly the kidney (Brown, 1979;Thoren, 1979). Moreoever, Chalmers et al (1967c) found, when studying the effects of hemorrhage on regional vascular resistance in conscious rabbits, that only in the case of the kidney did vasoconstriction occur that could not be accounted for by the arterial baroreceptor reflex. It is quite likely, therefore, that in our present study a major effect of the cardiac receptor reflex on the renal vasculature during blood volume depletion was concealed by the absence of 433 effects on other vascular beds.…”

Role of Vagal Afferents In the Control of Renal Sympathetic Nerve Activity in the Rabbit

“…Chalmers et al (11) observed that after sinoaortic denervation in the rabbit a 26% hemorrhage produced a small but sustained increase in renal vascular resistance. Oberg and White (1) demonstrated that after sinoaortic denervation in the cat a 20-ml hemorrhage caused an increase in the vascular resistance in the kidney greater than that in the muscular bed.…”

The origin of vasovagal syncope: to protect the heart or to escape predation?

“…The efferent pathway also appears to be the same: an increase in sympathetic tone is followed by withdrawal of the sympathetic system, as shown by the sudden decrease in BP and also by micro-neurographic recordings [12,49,60,67], and then by an increase in vagal tone, as shown by the slowing of HR. Since the vasovagal reflex during hemorrhagic shock has been observed in rats, rabbits, cats, dogs and monkeys, as well as in humans [12,14,22,38,49,50,52,57,59,67], this means that the orthostatic vasovagal reflex is predisposed in primates and other mammals.…”

“…The vasovagal reflex during hemorrhagic shock has been observed in mammals such as rats, rabbits, cats, dogs and rhesus monkeys, as well as in humans [12,14,23,38,49,50,52,57,59,67]. The hemodynamic response to acute central hypovolemia consists of two phases.…”