Reflex response of the rabbit hind‐limb muscle vascular bed to baroreceptor stimulation and its modification by pregnancy.

Humphreys, P. W.; Joels, N.

doi:10.1113/jphysiol.1982.sp014352

Cited by 9 publications

(6 citation statements)

References 13 publications

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“…Carotid sinus baroreflex depressor responses were equivalent, but pressor responses were attenuated in pregnant compared to nonpregnant animals. Subsequent studies revealed that this was due to attenuated increases in vascular resistance in nonuterine circulatory beds,9 rather than to attenuated changes in cardiac output10 during baroreceptor unloading (low carotid sinus pressure) in pregnant animals. Although these data suggest that autonomic neural mechanisms may be involved, interpretation of the results is complicated by the fact that vascular responsiveness to circulating and neurally released vasoconstrictors is decreased in pregnancy 11–13…”

Section: Effects Of Pregnancy On Arterial Baroreflex Functionmentioning

confidence: 99%

CNS Effects of Ovarian Hormones and Metabolites on Neural Control of Circulation

Heesch

Foley

2001

Annals of the New York Academy of Sciences

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Pregnant women often experience orthostatic hypotension, and pregnancy is associated with increased susceptibility to hemorrhagic hypotension. Experiments evaluating arterial baroreflex control of efferent sympathetic nerve activity in virgin and term‐pregnant rats revealed that arterial baroreflex sympathoexcitation is attenuated, while sympathoinhibitory responses are well‐maintained or potentiated. Following a hypotensive challenge, pregnant animals exhibit attenuated Fos expression in the rostral ventrolateral medulla (RVLM), suggesting that unloading of arterial baroreceptors results in less excitation of presympathetic neurons in the brain stem. Other experiments, in which afferent baroreceptor discharge was recorded, suggest that this was not due to differences in afferent baoreceptor function. GABAergic mechanisms are responsible for tonic inhibition of sympathoexcitatory neurons in the RVLM and the major metabolite of progesterone, 3α‐OH‐dihydroprogesterone (3α‐OH‐DHP), which is elevated in pregnancy, is the most potent endogenous positive modulator of CNS GABAA receptor function. Additional experiments revealed that acutely administered 3α‐OH‐DHP, either intravenously or directly into the RVLM, mimicked the effects of pregnancy on baroreflex control of efferent sympathetic nerve activity and potentiated pressure sensitivity of spinally projecting RVLM neurons. Preliminary experiments using semiquantitative RT‐PCR, evaluated the relative expression of three subunits (α1–3) of the GABAA receptor, and suggest that chronic exposure to elevated levels of ovarian hormones can result to changes in GABAA receptor subunit composition. It is likely that changes in control of sympathetic outflow in pregnancy are related to complex interactions between genomic and nongenomic actions of ovarian hormones and metabolites.

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Section: Effects Of Pregnancy On Arterial Baroreflex Functionmentioning

confidence: 99%

CNS Effects of Ovarian Hormones and Metabolites on Neural Control of Circulation

Heesch

Foley

2001

Annals of the New York Academy of Sciences

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“…Details of the recordingprocedures and the measurement ofblood gases have been given (Humphreys & Joels, 1982).…”

Section: Methodsmentioning

confidence: 99%

“…1). The arterial inflow to the left hind limb was vascularly isolated and the limb perfused as described in the preceding paper (Humphreys & Joels, 1982) with the exception that the perfusion pump was supplied with blood from the left common carotid artery. Two series of experiments were performed: in one the skin of the perfused hind limb remained in situ; in the other the limb was skinned as previously described to restrict the circulation largely to muscle.…”

Section: Methodsmentioning

confidence: 99%

“…Since the uterine blood flow near term is only about 7 % of cardiac output (Duncan, 1969) we have looked in other beds for changes which might contribute to this fall. In the preceding paper (Humphreys & Joels, 1982) we reported the effect of pregnancy on the reflex response of the perfused hind-limb muscle bed to carotid sinus baroreceptor stimulation; at a given level of sinus pressure and with the limb perfused at the same constant flow, perfusion pressure in the hind limb of the pregnant rabbit was lower than in the non-pregnant animal, i.e. the vascular resistance of the limb was lower under these conditions.…”

Section: Introductionmentioning

confidence: 99%

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The response of the hind‐limb vascular bed of the rabbit to sympathetic stimulation and its modification by pregnancy.

Humphreys¹,

Joels²

1982

The Journal of Physiology

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SUMMARY1. Pressure-flow relationships in the hind limb, perfused with blood at a series of constant flows, have been compared in primigravid and virgin rabbits following section of the lumbar sympathetic chain.2. In the absence of sympathetic stimulation perfusion pressure was lower (P < 0 05) in the pregnant rabbits at all levels of flow to the leg.3. It is concluded that pregnancy leads to a reduction in the vascular resistance of the acutely sympathectomized hind limb.4. The pressure-flow curves of hind limbs from pregnant and non-pregnant rabbits in which the cutaneous circulation had been excluded by skinning the leg and ligating the ankle were also compared. Again, perfusion pressure at each flow level was lower in the limbs from the pregnant animals (P < 0 05).5. The sympathetic supply was stimulated at frequencies of 0 3, 1, 3, 7, 15 and 30 Hz. Irrespective of whether the cutaneous circulation was excluded, the pressureflow curves for the hind limbs of pregnant and non-pregnant rabbits were different at the lower frequencies. As stimulus frequency rose this difference became smaller, and at a stimulus frequency of 7-15 Hz or more there was little difference in the position of the curves in pregnant and non-pregnant rabbits.6. Examination of the pressure-flow curves suggests that when, as in these experiments, flow is held constant, the ability of sympathetic stimulation to increase the resistance to blood flow is reduced in pregnancy. However, if these pressure-flow curves are used to predict the change of flow that would occur at a constant perfusion pressure, the response to sympathetic stimulation appears to be greater in pregnancy.7. Futher analysis of the findings, based on certain assumptions, suggests that differences between the pressure-flow curves of pregnant and non-pregnant animals during sympathetic stimulation are due in the main to either a differing size of the unstimulated vascular beds or a differing compliance of their vessel walls, rather than to any intrinsic alteration in their response to sympathetic stimulation.

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“…Further details of the perfusion and the various checks for completeness of vascular isolation have been given previously (Humphreys & Joels, 1982a …”

Section: Preparation Of 8inu8 Aortic and Lumbar Sympathetic Nervesmentioning

confidence: 99%

The effect of pregnancy on the changes in hind‐limb vascular resistance following haemorrhage in the rabbit.

Humphreys¹,

Joels²

1986

The Journal of Physiology

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SUMMARY1. The change in vascular resistance of the skinned hind limb perfused at constant flow has been measured following rapid removal of 10 % of the blood volume in anaesthetized pregnant rabbits (27-29 days gestation) and compared with that of non-pregnant rabbits.2. 5 s after haemorrhage was completed vascular resistance had risen in all rabbits, but in the pregnant ones this increase was only one-fifth of that in the non-pregnant ones.3. After section of either the carotid sinus and aortic nerves or the sympathetic innervation to the hind limb the increases of vascular resistance at this time were abolished.4. It is concluded that the previously described diminution during pregnancy of the protective function of the baroreflexes during haemorrhage results, to some extent, from their diminished role in a vascular bed not associated with the reproductive process.5. The blood withdrawn was not re-infused for 10 min, throughout which, in all rabbits with sinus, aortic and sympathetic nerves intact, the increase in vascular resistance was sustained.6. After section of the carotid sinus and aortic nerves and the sympathetic innervation there was, during this 10 min, a slow increase in vascular resistance comparable in final size to that which occurred immediately in the respective innervated preparations, i.e. it was smaller in the pregnant than in the non-pregnant rabbits.7. A possible difference in action during pregnancy of a vasoconstrictor substance released during haemorrhage is discussed briefly.

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Reflex response of the rabbit hind‐limb muscle vascular bed to baroreceptor stimulation and its modification by pregnancy.

Cited by 9 publications

References 13 publications

CNS Effects of Ovarian Hormones and Metabolites on Neural Control of Circulation

CNS Effects of Ovarian Hormones and Metabolites on Neural Control of Circulation

The response of the hind‐limb vascular bed of the rabbit to sympathetic stimulation and its modification by pregnancy.

The effect of pregnancy on the changes in hind‐limb vascular resistance following haemorrhage in the rabbit.

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