Characterisation of the effects of natriuretic peptides upon ACTH secretion from the mouse pituitary

Inhibitory action of B-type natriuretic peptide on adrenocorticotropic hormone in patients with acute coronary syndrome

In addition to the classical actions of hemodynamic regulation, natriuretic peptides (NPs) interact with various neurohumoral factors that are deeply involved in the pathophysiology of cardiovascular diseases. However, their effects on the hypothalamic-pituitary-adrenal (HPA) axis, which is activated under acute high-stress conditions in acute coronary syndrome (ACS), remain largely unknown. We investigated the impact of plasma B-type NP (BNP) on plasma adrenocorticotropic hormone (ACTH)-cortisol levels during the acute phase of ACS ischemic attacks. The study population included 436 consecutive patients with ACS for whom data were collected during emergency cardiac catheterization. Among them, biochemical data after acute-phase treatment were available in 320 cases, defined as the ACS-remission phase (ACS-rem). Multiple regression analyses revealed that plasma BNP levels were significantly negatively associated with plasma ACTH levels only during ACS attacks (P < 0.001), but not in ACS-rem, whereas plasma BNP levels were not significantly associated with plasma cortisol levels at any point. Accordingly, covariance structure analyses were performed to clarify the direct contribution of BNP to ACTH by excluding other confounding factors, confirming that BNP level was negatively correlated with ACTH level only during ACS attacks (β = -0.152, P = 0.002), whereas BNP did not significantly affect ACTH in ACS-rem. In conclusion, despite the lack of a significant direct association with cortisol levels, BNP negatively regulated ACTH levels during the acute phase of an ACS attack in which the HPA axis ought to be activated. NP may alleviate the acute stress response induced by severe ischemic attacks in patients with ACS.NEW & NOTEWORTHY BNP negatively regulates ACTH during a severe ischemic attack of ACS in which hypothalamic-pituitary-adrenal axis ought to be activated, indicating an important role of natriuretic peptides as a mechanism of adaptation to acute critical stress conditions in humans.

C-type natriuretic peptide (CNP) in the paraventricular nucleus-mediated renal sympatho-inhibition

Volume reflex produces sympatho-inhibition that is mediated by the hypothalamic paraventricular nucleus (PVN). However, the mechanisms for the sympatho-inhibitory role of the PVN and the neurochemical factors involved remain to be identified. In this study, we proposed C-type natriuretic peptide (CNP) as a potential mediator of this sympatho-inhibition within the PVN. Microinjection of CNP (1.0 μg) into the PVN significantly decreased renal sympathetic nerve activity (RSNA) (−25.8% ± 1.8% vs. −3.6% ± 1.5%), mean arterial pressure (−15.0 ± 1.9 vs. −0.1 ± 0.9 mmHg) and heart rate (−23.6 ± 3.5 vs. −0.3 ± 0.9 beats/min) compared with microinjection of vehicle. Picoinjection of CNP significantly decreased the basal discharge of extracellular single-unit recordings in 5/6 (83%) rostral ventrolateral medulla (RVLM)-projecting PVN neurons and in 6/13 (46%) of the neurons that were not antidromically activated from the RVLM. We also observed that natriuretic peptide receptor type C (NPR-C) was present on the RVLM projecting PVN neurons detected by dual-labeling with retrograde tracer. Prior NPR-C siRNA microinjection into the PVN significantly blunted the decrease in RSNA to CNP microinjections into the PVN. Volume expansion-mediated reduction in RSNA was significantly blunted by prior administration of NPR-C siRNA into the PVN. These results suggest a potential role for CNP within the PVN in regulating RSNA, specifically under physiological conditions of alterations in fluid balance.

Do N-Terminal Pro-C-Type Natriuretic Peptide Levels Relate to Severity of Preeclampsia?

Aim

To compare the plasma N-terminal pro-C-type natriuretic peptide concentrations of normotensive pregnant women, patients with mild preeclampsia, and patients with severe preeclampsia.

Methods

We collected venous blood samples from 25 normotensive pregnant women, 15 patients with mild preeclampsia, and 15 patients with severe preeclampsia. The women were at 30th to 40th weeks of gestation and in an age range of 20 to 35. The N-terminal pro-C-type natriuretic peptide levels were measured by ELISA. Statistical comparisons were made by one-way analysis of variance, Kruskal–Wallis, and Mann–Whitney U tests.

Results

The median (interquartile range-IQR) values of the N-terminal pro-C-type natriuretic peptide were 6.48 (3.33) pmol/L in the normotensive women group, 7.37 (3.43) pmol/L in patients with mild preeclampsia, and 11.52 (6.13) pmol/L in patients with severe preeclampsia. The N-terminal pro-C-type natriuretic peptide was significantly elevated in the severe preeclampsia study group (P < 0.001), whereas there was no significant difference between those with mild preeclampsia and the normotensive groups (P > 0.05).

Conclusion

Our data indicate that the plasma concentration of the N-terminal pro-C-type natriuretic peptide is significantly increased in patients with severe preeclampsia, but not in patients with mild preeclampsia. The severity of preeclampsia may be related to the circulating levels of the N-terminal pro-C-type natriuretic peptide concentrations.

The effect of natriuretic C-type peptide and its change over time on mortality in patients on haemodialysis or haemodiafiltration

Background

C-type natriuretic peptide (CNP) and its co-product N-terminal proCNP (NTproCNP) have been associated with beneficial effects on the cardiovascular system. In prevalent dialysis patients, however, a relation between NTproCNP and mortality has not yet been investigated. Furthermore, as a middle molecular weight substance, its concentration might be influenced by dialysis modality.

Methods

In a cohort of patients treated with haemodialysis (HD) or haemodiafiltration (HDF), levels of NTproCNP were measured at baseline and 6, 12, 24 and 36 months. The relation between serum NTproCNP and mortality and the relation between the 6-month rate of change of NTproCNP and mortality were analysed using Cox regression models. For the longitudinal analyses, linear mixed models were used.

Results

In total, 406 subjects were studied. The median baseline serum NTproCNP was 93 pmol/L and the median follow-up was 2.97 years. No relation between baseline NTproCNP or its rate of change over 6 months and mortality was found. NTproCNP levels remained stable in HD patients, whereas NTproCNP decreased significantly in HDF patients. The relative decline depended on the magnitude of the convection volume.

Conclusions

In our study, levels of NTproCNP appear strongly elevated in prevalent dialysis patients. Second, while NTproCNP remains unaltered in HD patients, its levels decline in individuals treated with HDF, with the decline dependent on the magnitude of the convection volume. Third, NTproCNP is not related to mortality in this population. Thus NTproCNP does not seem to be a useful marker for mortality risk in dialysis patients.

Expression of guanylyl cyclase-B (GC-B/NPR2) receptors in normal human fetal pituitaries and human pituitary adenomas implicates a role for C-type natriuretic peptide

C-type natriuretic peptide (CNP/Nppc) is expressed at high levels in the anterior pituitary of rats and mice and activates guanylyl cyclase B receptors (GC-B/Npr2) to regulate hormone secretion. Mutations in NPR2/Npr2 can cause achondroplasia, GH deficiency, and female infertility, yet the normal expression profile within the anterior pituitary remains to be established in humans. The current study examined the expression profile and transcriptional regulation of NPR2 and GC-B protein in normal human fetal pituitaries, normal adult pituitaries, and human pituitary adenomas using RT-PCR and immunohistochemistry. Transcriptional regulation of human NPR2 promoter constructs was characterized in anterior pituitary cell lines of gonadotroph, somatolactotroph, and corticotroph origin. NPR2 was detected in all human fetal and adult pituitary samples regardless of age or sex, as well as in all adenoma samples examined regardless of tumor origin. GC-B immunoreactivity was variable in normal pituitary, gonadotrophinomas, and somatotrophinomas. Maximal transcriptional regulation of the NPR2 promoter mapped to a region within -214 bp upstream of the start site in all anterior pituitary cell lines examined. Electrophoretic mobility shift assays revealed that this region contains Sp1/Sp3 response elements. These data are the first to show NPR2 expression in normal human fetal and adult pituitaries and adenomatous pituitary tissue and suggest a role for these receptors in both pituitary development and oncogenesis, introducing a new target to manipulate these processes in pituitary adenomas.

In vitro effects of homologous natriuretic peptides on growth hormone and prolactin release in the tilapia, Oreochromis mossambicus

C-type natriuretic peptide (CNP) cDNA was cloned from the tilapia brain and its inferred mature sequence was chemically synthesized together with previously cloned tilapia A-type and B-type natriuretic peptides (ANP and BNP). The cloned CNP belongs to the CNP-1 type of teleosts. Reverse-transcription polymerase chain reaction showed that the ANP and BNP genes were hardly expressed in the tilapia brain and pituitary, whereas the CNP gene was expressed strongly in the brain and slightly in the pituitary. Effects of homologous natriuretic peptides (100 nM each) on growth hormone (GH) and prolactin (PRL) release were examined using dispersed tilapia pituitary cells. Tilapia ANP and BNP stimulated GH and PRL release during 4-8, and 8-24 h of incubation. BNP appeared to be more potent than ANP, also stimulating GH and PRL release during 0-4 h of incubation. CNP stimulated GH release only during 4-8 h of incubation; CNP was without effect on PRL release. All three NPs stimulated GH and PRL mRNA expression in dispersed pituitary cells following 24 h of incubation. ANP and BNP significantly elevated intracellular cGMP accumulation in dispersed pituitary cells after 15 min of exposure, whereas no effect of CNP was observed. These results indicate a long-lasting stimulation of GH and PRL release by ANP and BNP that is mediated, at least in part, by the guanylyl cyclase-linked NP receptor.

C-type natriuretic peptide in vascular physiology and disease

Natriuretic peptides play a critical role in coordination of fluid/electrolyte balance and vascular tone. The renal effects of circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are distinct from the paracrine effects of vascular C-type natriuretic peptide (CNP). CNP is widely expressed throughout the vasculature and is found in particularly high concentrations in the endothelium. Recent studies demonstrate that CNP is a novel endothelium-derived hyperpolarising factor (EDHF) that complements the actions of other endothelial vasorelaxant mediators such as nitric oxide (NO) and prostacyclin. Since several cardiovascular disorders are associated with dysfunction of natriuretic peptide activity, selective modulation of the natriuretic peptide pathways represents an important therapeutic target; whilst this has been exploited to some degree in terms of ANP/BNP, the therapeutic potential of CNP has yet to be tapped. This review focuses on recent findings on the actions and mechanism of locally produced endothelial-derived CNP in the cardiovascular system and highlights many potential avenues for therapeutic intervention, via modulation of CNP-signalling, in cardiovascular disease.

C-type natriuretic peptide: an important neuroendocrine regulator?

In the decade since its discovery, C-type natriuretic peptide (CNP), the third member of the natriuretic peptide family, has been shown to be produced by most of the major endocrine glands, including the hypothalamus and anterior pituitary. The relative abundance of its guanylyl cyclase-containing GC-B receptor in these glands suggests that CNP might be a local neuroendocrine regulator. Here, we review this possibility, emphasizing signalling and integration with other regulatory systems in the neuroendocrine control of reproduction.