Noradrenaline attenuates the natriuretic effect of atrial natriuretic factor in man

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.

Insulin blunts the natriuretic action of atrial natriuretic peptide in hypertension

Hyperinsulinemia and insulin resistance are implicated in the etiology of hypertension, but the mechanisms involved have not been established. The objectives of this study were to determine whether untreated essential hypertensive patients are more sensitive to the antinatriuretic action of insulin and more resistant to the counteracting natriuretic effect of atrial natriuretic peptide in contrast to age- and sex-matched normotensive control subjects. Urinary sodium excretion was measured at baseline, during hyperinsulinemic euglycemic clamp, and during coadministration of insulin and atrial natriuretic peptide. Baseline urinary sodium excretion was not significantly different in the normotensive subjects (415 +/- 47 mumol/min, n = 12) and hypertensive patients (381 +/- 18 mumol/min, n = 10); with the institution of insulin infusion, there was a similar and significant decline from baseline (P < .001) to 289 +/- 35 mumol/min in normotensive subjects and 235 +/- 17 mumol/min in hypertensive patients. Atrial natriuretic peptide was able to oppose the antinatriuretic action of insulin in normotensive subjects, increasing urinary sodium excretion significantly to a mean level of 352 +/- 31 mumol/min (P < .05), which did not differ significantly from baseline. In the hypertensive group, atrial natriuretic peptide infusion had no effect on urinary sodium excretion (238 +/- 18 mumol/min), and the difference from baseline remained highly significant (P < .001). The hypertensive patients were significantly less insulin sensitive than their normotensive counterparts, as reflected by a lower glucose utilization rate and higher mean baseline plasma insulin level (P < .05 for each).(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide in heart failure

Atrial natriuretic peptide hormone of cardiac origin, which is released in response to atrial distension and serves to maintain sodium homeostasis and inhibit activation of the renin-angiotensin-aldosterone system. Congestive heart failure is a clinical syndrome characterized by increased cardiac volume and pressure overload with an inability to excrete a sodium load, which is associated with increased activity of systemic neurohumoral and local autocrine and paracrine mechanisms. Circulating atrial natriuretic peptide is greatly increased in congestive heart failure as a result of increased synthesis and release of this hormone. Atrial natriuretic peptide has emerged as an important diagnostic and prognostic serum marker in congestive heart failure. In early heart failure, it may play a key role in preserving the compensated state of asymptomatic left ventricular dysfunction. Despite increased circulating atrial natriuretic peptide in heart failure, the kidney retains sodium and is hyporesponsive to exogenous and endogenous atrial natriuretic peptide. The mechanism for the attenuated renal response is multifactorial and includes renal hypoperfusion, activation of the renin-angiotensin-aldosterone and sympathetic nervous systems. Therapeutic strategies to potentiate the biologic actions of atrial natriuretic peptide may prolong the asymptomatic phase and delay progression to overt congestive heart failure.

Renal effects of xamoterol in patients with moderate heart failure

The acute renal effects of xamoterol, a partial beta 1-agonist, were studied in 12 patients with congestive heart failure (NYHA II-III) in stable condition on diuretic therapy for at least 6 weeks. Each patient was given a single intravenous infusion of xamoterol (0.2 mg/kg) or placebo in random order 2 weeks apart. Using constant infusion and lithium clearance techniques, clearance and excretion measurements were made in the supine position at 30- to 60-min intervals before, during, and up to 6 hours after infusion. Blood pressure, heart rate, renal plasma flow, glomerular filtration rate, and urinary flow rate remained unchanged, but xamoterol lowered sodium excretion by 30% (p < 0.05). The decrease started 120 minutes after infusion. Proximal reabsorption of sodium increased after xamoterol infusion, whereas plasma values of aldosterone and angiotensin II were unaffected. It is concluded that the acute renal effects of xamoterol imply an impaired sodium excretion determined by the tubular actions of the drug. The present results suggest that xamoterol may aggravate one of the important abnormalities intrinsic to the pathology of congestive heart failure. These findings are in contrast to the beneficial effects of xamoterol demonstrated in many clinical trials where xamoterol was given orally for a longer period.

Interactions between atrial natriuretic factor and the autonomic nervous system

In addition to its natriuretic, hormonal and vascular actions, atrial natriuretic factor (ANF) may interact importantly with the function of the autonomic nervous system. It has been hypothesized that ANF may exert its cardiovascular and possibly renal effects by interfering with autonomic control mechanisms. In, animal experiments the hypotension that is caused by ANF is usually not associated with the expected reflex tachycardia or increased efferent sympathetic activity. Furthermore, bilateral vagotomy can attenuate the hypotensive action of ANF which suggest that ANF may stimulate sympathoinhibitory afferent vagal activity from the cardiopulmonary baroreceptor system. In man, ANF may alter reflexogenic-mediated forearm vascular responses to cardiopulmonary deactivation which suggest that ANF may have an important role as a neuromodulator of autonomic nervous function, a role that could serve to amplify or facilitate the peripheral hormonal actions of ANF. This neuromodulating influence of ANF could be due to several mechanisms: it could modulate baroreflex mechanisms or it could have direct effects on autonomic centres in the brain or it could have effects on peripheral neurotransmission. The role of the autonomic nervous system in modulating the release of ANF remains controversial. Finally, there is growing evidence to suggest that there is a reciprocal interplay between ANF and the sympathetic nervous system in peripheral target tissues which may have important pathophysiological significance.

DOPA decarboxylase inhibition does not influence the diuretic and natriuretic response to exogenous alpha-atrial natriuretic peptide in man

The role of dopamine synthesis in the renal actions of human alpha-atrial natriuretic peptide (alpha ANP) was investigated in six dehydrated volunteers using the DOPA decarboxylase inhibitor carbidopa. Each subject received oral placebo or carbidopa (100 mg) followed by an infusion of alpha ANP 10 pmol.kg-1.min-1 for 1 h. The responses to placebo alone and to carbidopa alone were investigated on separate occasions. alpha ANP produced a similar increase in plasma immunoreactive alpha ANP whether placebo or carbidopa pretreatment had been given. Urinary dopamine excretion was increased by alpha ANP. Carbidopa pretreatment substantially attenuated this increase without affecting the natriuretic or water-diuretic response to alpha ANP. Carbidopa also failed to alter the change in filtration fraction produced by alpha ANP. The results suggest that increased synthesis of intrarenal dopamine is not required for the renal effects of alpha ANP in man.