The effect of discrete stimulation of carotid body chemoreceptors on atrial natriuretic peptide in anaesthetized dogs

Hypoxia regulates the natriuretic peptide system

Numerous clinical studies have addressed the role of the natriuretic peptide system either as a diagnostic tool or as a guide to treatment in many cardiac diseases. The concept behind these studies has been that intravascular overload produces cardiac wall stress that alone stimulates the synthesis and release of natriuretic peptides the result of which is diuresis, natriuresis, and vasodilatation. However, almost thirty years after the discovery of the natriuretic peptides the measurement of these peptides, especially the BNP, has not met all the expectations of a simple and useful diagnostic tool in clinical cardiology, possibly due to confounding factors confusing the interpretation of the wall stress effect. In the same way as in pressure studies, it has been shown that hypoxia is a direct and sufficient stimulus for the synthesis and release of ANP and BNP. Additionally, hypoxia-response elements have been characterized from the promoter sequence of both the ANP and the BNP genes. Furthermore, a physiological rhythm (eupnea-apnea), causing changes in blood oxygen tension, regulates the plasma levels of ANP in sleeping seal pups which are spontaneously able to hold back their breathing. We suggest, on the basis of the extensive published literature, that the stimulus for the synthesis and release of natriuretic peptides is the oxygen gradient which always occurs in all human tissues in physiological conditions. The plasma volume contraction caused by natriuretic peptides (natriuresis, diuresis, and plasma shift) leads to hemoconcentration and ultimately to the increased oxygen-carrying capacity of unit volume of blood.

Atrial natriuretic peptide stimulates cat carotid body chemoreceptors in vivo

It is known that atrial natriuretic peptide (ANP) is released from cardiac myocyte and other stores during hypoxia and is involved in pulmonary-cardiovascular reflexes and in natriuresis and diuresis. Since the carotid body initiates hypoxic chemoreflexes, we hypothesized that ANP could potentiate the hypoxic stimulation of the carotid body chemoreceptor in vivo. We studied the effect of close intra-arterial injection of ANP on carotid chemoreceptor activity in anesthetized male cats which were paralyzed and artificially ventilated. Graded doses of ANP (0-10 nmoles) were administered by intra-arterial injections and they produced an excitatory response. Single dose of ANP (6.5 nmoles) at four steady-state levels of arterial PO(2), at constant PCO(2), produced increases of chemoreceptor activity. This increase of chemoreceptor activity with ANP in the presence of CO(2)-HCO(3)(-) in vitro could make a difference from those without CO(2)-HCO(3)(-) in vivo.

Modification of carotid chemoreceptor-induced changes in renal haemodynamics and function by carotid baroreflex in dogs

1. Mongrel dogs were anaesthetized with thiopental sodium and chloralose and artificially ventilated. The carotid sinus regions were vascularly isolated and perfused either with arterial or mixed (arterial and venous) blood (PO2, 44.2 +/- 3.3 mmHg, mean +/- S.E.M.) to stimulate the chemoreceptors. Cervical vagosympathetic trunks were ligated and atenolol (2 mg kg-1, I.V.) was given in all dogs and gallamine triethiodide (3 mg kg-1 h-1, I.V.) was given in two dogs. Renal blood flow was measured by an electromagnetic flowmeter, glomerular filtration rate by creatinine clearance, sodium excretion by flame photometry and solute excretion by osmometry. The viability of the preparations was tested by recording total vascular capacitance responses to stimulation of carotid baro- and chemoreceptors. 2. In eleven tests in seven dogs at a constant aortic pressure of 88.9 +/- 2.6 mmHg stimulation of carotid chemoreceptors at a high carotid sinus pressure (194.0 +/- 3.6 mmHg) resulted in significant increases in urine flow of 22.8 +/- 3.0%, urinary sodium excretion of 30.7 +/- 5.2%, fractional sodium excretion of 35.3 +/- 18.6%, osmolar excretion of 17.5 +/- 4.1% and a decrease in free water clearance of 30.8 +/- 3.1% without significant changes in urinary sodium concentration, renal blood flow, glomerular filtration rate, and filtration fraction. 3. In seventeen tests in these seven dogs at a constant aortic pressure of 94.0 +/- 2.2 mmHg, stimulation of carotid chemoreceptor at a low carotid sinus pressure (72.0 +/- 1.3 mmHg) resulted in significant decreases in renal blood flow of 10.6 +/- 2.5%, glomerular filtration rate of 19.6 +/- 6.8%, filtration fraction of 13.2 +/- 5.5%, urine flow of 23.4 +/- 4.1%, urinary sodium concentration of 20.3 +/- 4.1%, urinary sodium excretion of 38.5 +/- 4.6%, fractional sodium excretion of 20.2 +/- 7.7%, osmolar excretion of 23.9 +/- 4.0% and an increase in free water clearance of 23.1 +/- 2.5%. 4. The results show that moderate stimulation of carotid chemoreceptors at a low carotid sinus pressure, when the activity in renal nerves is high and blood volume is low, can produce significant reflex decreases in renal haemodynamic and functional variables. However, at a high carotid sinus pressure when the renal sympathetic activity is low and blood volume is high, carotid chemoreceptor stimulation produces diuresis and natriuresis but no change in renal haemodynamics.

Primary effects of carotid chemoreceptor stimulation on gracilis muscle and renal blood flow and renal function in dogs

1. In chloralose-anaesthetized and artificially ventilated dogs, the carotid sinus regions were vascularly isolated and perfused either with arterial or mixed (arterial and venous) blood (partial pressure of O2 (PO2) 43.8 +/- 2.4 mmHg, mean +/- S.E.M. n = 14) to stimulate the carotid chemoreceptors. The carotid sinus pressure was held constant at 142.0 +/- 2.8 mmHg. Measurements were made of renal and gracilis muscle blood flow by wrap-round electromagnetic flow probes placed around the renal and gracilis arteries, glomerular filtration rate by creatine clearance, urinary sodium excretion by flame photometry and solute excretion by osmometry. 2. In ten dogs, with intact cervical vagosympathetic trunks, carotid chemoreceptor stimulation produced significant increases in aortic pressure (AoP) of 12.7 +/- 1.1% (n = 10, P < 0.001), in glomerular filtration rate (GFR) of 14.7 +/- 4.1% (P < 0.001), urine flow rate (V) of 16.5 +/- 3.5% (P < 0.002), in urinary sodium excretion (UNaV) of 17.5 +/- 2.5% (P < 0.005) and in urinary osmolar excretion (UosmV) of 13.2 +/- 2.2% (P < 0.001), but a significant decrease in renal blood flow (RBF) of 5.8 +/- 1.8% (P < 0.02). In six of these dogs in which gracilis muscle blood flow (MBF) was also recorded, carotid chemoreceptor stimulation caused significant increases in AoP of 12.8 +/- 1.4% (n = 6, P < 0.001) and in MBF of 10.0 +/- 1.6% (P < 0.002), and a small but significant decrease in RBF of 3.6 +/- 1.5% (P < 0.02). 3. In fourteen dogs, with sectioned cervical vagosympathetic trunks, carotid chemoreceptor stimulation produced increases in AoP of 22.0 +/- 2.6% (n = 14, P < 0.001), in GFR of 36.9 +/- 4.2% (P < 0.001), in V of 30.1 +/- 4.4% (P < 0.001), in UNaV of 31.4 +/- 5.3% (P < 0.001), and in UosmV of 25.7 +/- 5.8% (P < 0.001). However, it produced a greater decrease in RBF of 10.5 +/- 1.9% (P < 0.001). In ten of these dogs, where MBF was recorded, carotid chemoreceptor stimulation caused greater increase in AoP of 22.4 +/- 3.0% (n = 10, P < 0.001) and in MBF of 32.8 +/- 3.7% (P < 0.001), and a greater decrease in RBF of 9.8 +/- 1.9% (P < 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

Normotensive normoxic men undergoing water diuresis fail to respond to stimulation of their peripheral arterial chemoreceptors by almitrine with an increase in plasma concentrations of atrial natriuretic factor

The purpose of this study was to investigate the possible participation of atrial natriuretic factor (ANF) in the natriuretic and diuretic response occurring after stimulation of the peripheral arterial chemoreceptors by almitrine bismesylate in normoxic humans. The experiments were performed in 14 healthy male volunteers undergoing water diuresis. Each subject participated in two experiments. In one of them they ingested 100-mg almitrine at 12 p.m. The other study served as a control. Surprisingly, our subjects responded to almitrine with an elevation of urine flow only, whereas sodium excretion remained almost unchanged over the whole period of the experiments. As regards ANF plasma concentrations, no statistically significant differences between the control and the almitrine group could be observed. Moreover, no direct connection between ANF plasma concentrations and renal volume excretion was detectable. We conclude that a specific stimulation of peripheral arterial chemoreceptors by almitrine in humans undergoing water diuresis did not seem to raise ANF plasma concentrations as is the case at high altitude. Therefore we would suggest that there exists no specific reflex influence of these receptors on ANF release.