Hemodynamic effects of atrial natriuretic peptide in conscious sheep

Natriuretic Peptides and Normal Body Fluid Regulation

Natriuretic peptides are structurally related, functionally diverse hormones. Circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are delivered predominantly by the heart. Two C-type natriuretic peptides (CNPs) are paracrine messengers, notably in bone, brain, and vessels. Natriuretic peptides act by binding to the extracellular domains of three receptors, NPR-A, NPR-B, and NPR-C of which the first two are guanylate cyclases. NPR-C is coupled to inhibitory proteins. Atrial wall stress is the major regulator of ANP secretion; however, atrial pressure changes plasma ANP only modestly and transiently, and the relation between plasma ANP and atrial wall tension (or extracellular volume or sodium intake) is weak. Absence and overexpression of ANP-related genes are associated with modest blood pressure changes. ANP augments vascular permeability and reduces vascular contractility, renin and aldosterone secretion, sympathetic nerve activity, and renal tubular sodium transport. Within the physiological range of plasma ANP, the responses to step-up changes are unimpressive; in man, the systemic physiological effects include diminution of renin secretion, aldosterone secretion, and cardiac preload. For BNP, the available evidence does not show that cardiac release to the blood is related to sodium homeostasis or body fluid control. CNPs are not circulating hormones, but primarily paracrine messengers important to ossification, nervous system development, and endothelial function. Normally, natriuretic peptides are not powerful natriuretic/diuretic hormones; common conclusions are not consistently supported by hard data. ANP may provide fine-tuning of reno-cardiovascular relationships, but seems, together with BNP, primarily involved in the regulation of cardiac performance and remodeling. © 2017 American Physiological Society. Compr Physiol 8:1211-1249, 2018.

The effect of hypovolemia on the renal and cardiovascular responses to atrial natriuretic factor (ANF) infusion

The renal and cardiovascular effects of ANF infusion have been examined in separate series of experiments; in conscious instrumented sheep following either hemorrhage (10 mL/kg body weight) or removal of 500 mL of plasma by ultrafiltration. Renal arterial infusion of hANF (99-126) at 50 micrograms/h increased sodium excretion from 99 +/- 30 to 334 +/- 102 (p less than 0.05) in normal animals, and from 77 +/- 31 to 354 +/- 118 mumol/min in hemorrhaged animals. Similarly in sheep following ultrafiltration, cardiac output and stroke volume were reduced by intravenous infusion of ANF (100 micrograms/h), although these effects were less marked than those observed in normal animals. The rapid modulation of natriuretic responses to ANF observed in volume expanded animals is not seen in this model of acute volume depletion suggesting that the mechanism through which the renal response to ANF is modulated in low sodium or volume states is not simply the reverse of that which produces rapid enhancement of response following blood volume expansion.

Hemodynamic interactions of atrial natriuretic factor with the sympathetic nervous system in sheep

The hemodynamic effects of short-term infusion of atrial natriuretic factor (ANF) were observed in sheep with combined alpha/beta adrenoceptor pharmacological blockade. The effect of ANF on the sympathetically-mediated baroreflex system was observed in conscious sheep in which aortic and vena caval balloon occluders had been surgically implanted. ANF infused at 100 micrograms/h for 60 min produced similar effects on blood pressure, cardiac output and stroke volume during alpha/beta-adrenoceptor blockade, compared to the responses seen in normal sheep, however the increases in heart rate and total peripheral resistance were reduced. ANF markedly enhanced the gain of the baroreceptor-heart rate reflex in the sheep. This effect may mediate the large increase in heart rate which is associated with a small fall in blood pressure during short-term infusion of ANF. In conclusion, the sympathetic nervous system plays an important role in regulating the reflex cardiovascular responses to short-term infusion of ANF in sheep. The large species variation in the hemodynamic responses to ANF may be related to differing degrees of stimulation or inhibition of the baroreceptor system to affect heart rate and/or peripheral resistance.

Atrial natriuretic peptide

This report has reviewed some of the cardiovascular aspects of ANP. The emergence of the heart as an endocrine organ requires that numerous questions be asked with regard to the importance of ANP to anesthesia and surgery. It is clear that the interaction of the hormone with other vasoactive compounds, including anesthetic agents, requires further elucidation. The accumulation of more information regarding the regulation of ANP and its cardiovascular setting will define its role in hemodynamic homeostasis in the acute clinical setting. Questions of specific interest to the anesthesiologist that require elucidation are: (1) Does the presence of abnormal ANP levels, associated with specific disease states, affect perioperative cardiovascular function? (2) Do cardiac surgery and CPB affect ANP-adrenergic interaction? (3) What is the relationship among blood volume, blood pressure, cation metabolism, and the ANP-renin-angiotensin system in perioperative patients? (4) What is the role of ANP as a therapeutic modality in surgical patients?

Comparative hemodynamic actions of ANF-related peptides in conscious sheep

The rapid hemodynamic effects of several N- and C-terminal deleted fragments of ANF, a potent ANF analogue and the recently characterised brain natriuretic peptide (BNP) were investigated in conscious sheep, and compared to the rapid hemodynamic actions of ANF 1-28. The hypotensive potency of all peptides studied was as follows: ANF 1-28 = PLO58 greater than 5-27 = ANF 5-28 = BNP greater than ANF 7-28 greater than ANF 13-28 = ANF 5-25. All peptides reduced blood pressure via a decrease in total peripheral resistance, excluding ANF 5-25 and 13-28 which were without effect on any parameter measured. These changes were associated with reflex increases in both heart rate and cardiac output, and a slight reduction in stroke volume. The duration of hypotensive/vasodilator action of ANF 1-28, 5-27, 5-28, 7-28 and BNP was approximately 3-4 minutes, whereas that of PLO58 was 7-8 minutes. In conclusion, amino acid deletions from the C- and N-terminal of the ANF molecule reduced the hypotensive/vasodilator potency of the peptide in conscious sheep. BNP produced similar rapid hemodynamic changes to ANF 1-28, suggesting that the two peptides may co-regulate blood pressure and possibly body fluids to promote fluid and cardiovascular homeostasis.

The effects of intracerebroventricular administration of biologically active peptides in conscious sheep

The present study records the physiological effects of 24-hour intracerebroventricular infusion of a variety of biologically active peptides in conscious sheep. A number of peptides including AVP and TRH produced increases in mean arterial pressure, heart rate and body temperature. There was an overall positive correlation between peptide-induced changes in body temperature and changes in either mean arterial pressure or heart rate. TRH and beta-endorphin had marked effects on behaviour and several peptides reduced food and water intake. Several peptides increased urinary sodium excretion, however, few peptides changes plasma electrolyte concentrations. TRH produced small effects on plasma ACTH and plasma glucose concentrations. The peptides in this study produced physiological changes which were probably mediated by their actions on the central nervous system.

The effects of intracerebroventricular infusion of atrial natriuretic factor in conscious sheep

The effects of 24-hour intracerebroventricular infusion of human atrial natriuretic factor (ANF) and two related fragments were studied in conscious sheep. ANF (1-28) had no effect on either mean arterial pressure (MAP) or heart rate (HR) when infused at 3 or 10 micrograms/hr, however a small diuresis and an increase in urinary sodium (Na) excretion was observed. The smaller fragment, ANF (5-27) infused at 10 micrograms/hr, increased MAP, HR and body temperature, although the same rate of infusion of ANF (5-28) was without effect. All peptides increased plasma sodium concentration and plasma osmolality. None of the peptides affected plasma ACTH, glucose or renin concentration. ANF (1-28) had no effect on either Na intake or water intake in Na-depleted sheep. These studies suggest that members of the ANF family can influence a number of physiological functions following central administration.