Evolution of Cardiovascular Baroreceptor Control

Abstract

SummaryDuring animal evolution the circulatory system has shown a progressive modification in structure, function and short‐term control.Short‐term circulatory control has evolved from the limitation of a rising blood pressure via a reflex bradycardia to bidirectional control of blood pressure by appropriate reflex changes in heart rate, vascular resistance and impedance.Relevant experimental data ranges from extensive in mammals to nugatory in invertebrates. Baroreceptor research in intervening animal groups is varied, being particularly sparse in birds. This research is reviewed. There are few interspecies comparisons of baroreceptor physiology. Available data is complicated by variation in the techniques employed for assessing baroreceptor function. In non‐mammalian research the correlation of heart rate changes to pharmacologically induced changes in blood pressure predominate. In mammalian baroreceptor research methods based upon the ability of discrete baroreceptor sites to effect changes in the peripheral vasculature are more prevalent. All methods are susceptible to modification by other experimental variables, particularly the anaesthetic state of the animal.Available evidence shows a consistent response of a decreasing heart rate to baroreceptor loading throughout the vertebrates, with a progressive increase in the ability of the baroreceptors to change peripheral vascular resistance. These findings are consistent with the known, progressive trend from cholinergic to adrenergic control of the vascular system during evolution.Known baroreceptor sites appear to be located so as to protect the end‐organ or‐organs primarily at risk from inappropriate blood pressure changes; namely the gill vasculature in the fish, pulmonary circulation in the Amphibia and Reptilia, and the brain and heart in higher animal groups.It is postulated that the carotid sinus baroreceptors have developed in the Mammalia as a second functional baroreceptor site to provide extra protection against hypoperfusion of vital organs, particularly the heart and brain. In humans the dynamic aspects of cardiovascular carotid sinus control, particularly of skeletal muscle flow and integration with cardiopulmonary baroreceptors, may represent a specific response to the adoption of an upright stance. Extremes of environmental stress encountered in contemporary life may exceed the limitation of baroreceptor function in humans, as, for example, during gravitational loading particularly following periods of weightlessness and modification by endurance training.

Cardiac reflexes in a warming world: Thermal plasticity of barostatic control and autonomic tones in a temperate fish

“…The efferent cardiac branch of the barostatic reflex appears to be an evolutionarily ancient circulatory trait ubiquitous to all jawed vertebrates including fish (Bagshaw, 1985;Sandblom and Axelsson, 2011). While no previous study has explicitly examined the effects of temperature on baroreflex responses in fish, there is some information for other ectothermic vertebrates.…”

“…Similarly, assuming that the hypertensive bradycardia mainly serves to safeguard the respiratory tissues from hydrostatic pressure overload, it seems reasonable that this capacity should be relatively unaffected by environmental temperature, not least because the present study found that resting P VA was unaffected and responded similarly to the vasoactive drugs across environmental temperatures. Even so, as a closed-loop technique was employed in the present study, where vascular resistance and arterial blood pressure were pharmacologically manipulated, only the cardiac limb of the reflex was studied (for descriptions of closed-versus openloop experimental approaches see Bagshaw, 1985;Van Vliet and West, 1994). These technical limitations prevented us from examining the vascular limb of the baroreflex and determining how the recovery of arterial blood pressure homeostasis is affected by temperature.…”

“…the baroreflex) is a fundamental homeostatic cardiovascular mechanism in vertebrates, with the overall function to buffer changes in arterial blood pressure (Bagshaw, 1985;Jones and Milsom, 1982;Van Vliet and West, 1994). In fish, the gill vasculature is generally thought to be the main barosensitive area (Ristori, 1970;Ristori and Dessaux, 1970;Sundin and Nilsson, 2002), and at least in teleosts the efferent pathway of the reflex involves both a cardiac and a vascular limb Axelsson, 2005, 2011).…”

Baroreflex mediated control of heart rate and vascular capacitance in trout

“…Although neither abnormal behavioural responses nor increased mortality, indicative of brain damage, were observed even after repeated occlusions, the potential effects of this cannot be ignored. Bagshaw (1985) postulated that there has been an evolutionary transition amongst the vertebrates regarding the baroreflex. Regulation of cardiovascular homeostasis in the teleosts was claimed to be mainly heart-rate-based, whereas a more refined system including both cardiac and vascular properties first appears in the higher vertebrates.…”

REVERSIBLE CARDIAC ARREST INDUCED BY STARTLING STIMULI IN THE ANTARCTIC FISH Notothenia neglecta

“…RANDALL, 1968RANDALL, , 1970LAURENT et al, 1983;FARREL, 1984;BAGSHAW, 1985). Temperature elevation increases heart rate adjusting blood flow to the metabolic demands (PROSSER, 1973), acting directly on cardiac cells excitability (TSUKUDA et al, 1985).…”