Frog lymph heart synthesizes and stores immunoreactive atrial natriuretic peptide

The atrial natriuretic peptide (ANP) system in the pronephros and mesonephros of Bufo bufo larvae

In this study on the excretory apparatus of the Bufo bufo larvae, the ultrastructural features and the atrial natriuretic peptide (ANP)-system were examined using cytochemical and immunocytochemical methods. The early embryonic kidney, the pronephros, is replaced by a later stage, the mesonephros. The pronephros degenerates at the time of metamorphosis and the mesonephros becomes the functional kidney in the adult. Both these organs are targets for ANP, demonstrated by the presence of the specific receptors, indirectly highlighted by the cytochemical localization of the guanylate cyclase in the presence of exogenous atrial natriuretic peptide. This study concluded that the mesonephros produces ANP and thus clusters of cells containing ANP-like granules, positive to the anti-α ANP immunolocalization, were present along the mesonephric proximal tubule. The atrial natriuretic peptide system carries out an important osmoregulatory role in the excretory apparatus.

General Function and Endocrine Control of the Posterior Lymph Hearts inBufo marinusandRana catesbeiana

The effects of hypervolemia and graded increases in arginine vasotocin (AVT), angiotensin II (ANGII), and atrial natriuretic peptide (ANP) on lymph heart pressure (P(lh)) and rate (f(lh)) were examined in Bufo marinus and Rana catesbeiana. The P(lh) and f(lh) for normally hydrated B. marinus at rest were 1.45+/-0.01 kPa and 52.8+/-0.38 beats min(-1). The P(lh) and f(lh) were significantly lower in R. catesbeiana, 1.05+/-0.01 kPa and 48.4+/-0.35 beats min(-1). Hypervolemia, induced by intravenous infusion of isotonic saline, stopped the lymph hearts at volumes of 0.48%+/-0.06% and 0.32%+/-0.04% body mass in B. marinus and R. catesbeiana, respectively, equivalent to an 8% increase of their respective plasma volumes. ANP had no effect on P(lh) or f(lh) at any of the dosages tested. ANGII decreased f(lh) in both species, approximating the physiological range of concentrations. AVT, at physiological concentrations, increased P(lh) 48% in B. marinus and 38% in R. catesbeiana without changing f(lh) in either species. At higher than physiological dosages, P(lh) and f(lh) in both species declined. The results suggest that AVT, normally released during hemorrhage and dehydration, would increase lymph heart output and help compensate for the hypovolemia. This is a contrary result to previous work using supraphysiologic doses of AVT.

Comparative aspects of natriuretic peptide physiology in non-mammalian vertebrates: a review

The natriuretic peptide system is a complex family of peptides and receptors that is primarily linked to the maintenance of osmotic and cardiovascular homeostasis. A natriuretic peptide system is present in each vertebrate class but there are varying degrees of complexity in the system. In agnathans and chondrichthyians, only one natriuretic peptide has been identified, while new data has revealed that multiple types of natriuretic peptides are present in bony fish. However, it seems in tetrapods that there has been a reduction in the number of natriuretic peptide genes, such that only three natriuretic peptides are present in mammals. The peptides act via a family of guanylyl cyclase receptors to generate the second messenger cGMP, which mediates a range of physiological effects at key targets such as the gills, kidney and the cardiovascular system. This review summarises the current knowledge of the natriuretic peptide system in non-mammalian vertebrates and discusses the physiological actions of the peptides.

Proliferation and Differentiation Processes in the Heart Muscle Elements in Different Phylogenetic Groups

This article reviews, discusses, and summarizes data about the generative behavior of muscle tissue cells, the mechanisms of its regulation, and the organization of the endocrine function of the heart in the main phylogenetic groups. With respect to the ratio of processes of proliferation and differentiation, cell organization, and growth mechanism, muscle tissues of propulsive organs can be divided into three types, each revealed in one of three main groups of animals, lophotrochozoans, ecdysozoans, and chordates. Ecdysterone is likely to play the key role in the regulation of proliferation and differentiation processes in the heart muscle of crustaceans, and, most probably, also of molluscs. In each of the three main phylogenetic groups the endocrine function of the heart consisting of secretion of natriuretic peptides has a peculiar organization. Vertebrate cardiomyocytes are known to combine contractile and endocrine differentiation. Such functional dualism is absent in heart muscle elements of Lophotrochozoa and Ecdysozoa; in the heart of lopfotrochozoans, secretion of natriuretic peptides is performed by endothelial cells and their derivatives. Homology of the heart muscle in the animal kingdom as well as possible mechanisms of genomic and epigenomic regulation of different types of cardiomyogenesis are discussed.

Structural and functional evolution of the natriuretic peptide system in vertebrates

The natriuretic peptide (NP) system consists of three types of hormones [atrial NP (ANP), brain or B-type NP (BNP), and C-type NP (CNP)] and three types of receptors [NP receptor (R)-A, NPR-B, and NPR-C]. ANP and BNP are circulating hormones secreted from the heart, whereas CNP is basically a neuropeptide. NPR-A and NPR-B are membrane-bound guanylyl cyclases, whereas NPR-C is assumed to function as a clearance-type receptor. ANP, BNP, and CNP occur commonly in all tetrapods, but ventricular NP replaces BNP in teleost fish. In elasmobranchs, only CNP is found, even in the heart, suggesting that CNP is an ancestral form. A new guanylyl cyclase-uncoupled receptor named NPR-D has been identified in the eel in addition to NPR-A, -B, and -C. The NP system plays pivotal roles in cardiovascular and body fluid homeostasis. ANP is secreted in response to an increase in blood volume and acts on various organs to decrease both water and Na+, resulting in restoration of blood volume. In the eel, however, ANP is secreted in response to an increase in plasma osmolality and decreases Na+ specifically, thereby promoting seawater adaptation. Therefore, it seems that the family of NPs were originally Na(+)-extruding hormones in fishes; however, they evolved to be volume-depleting hormones promoting the excretion of both Na+ and water in tetrapods in which both are always regulated in the same direction. Vertebrates expanded their habitats from fresh water to the sea or to land during evolution. The structure and function of osmoregulatory hormones have also undergone evolution during this ecological evolution. Thus, a comparative approach to the study of the NP family affords new insights into the essential function of this osmoregulatory hormone.

Specific binding sites for atrial natriuretic peptide in the freshwater turtle, Amyda japonica

Specific binding sites for atrial natriuretic peptide (ANP) were investigated by in vitro autoradiographic techniques in various tissues of the freshwater turtle, Amyda japonica. A high density of binding sites for 200 pM of 125I-labelled rANP(1-28) was located in the glomeruli of the kidney and the cortical portion of the adrenal gland. A moderate density of binding sites was seen in the arachnoid matter and choroid plexus of the third and lateral ventricles of the brain and the epididymis. A low density of binding sites was revealed in lamina propria of the mucosa of stomach and intestine, the seminiferous tubules of testes, and the epithelial layer of oviduct. In the presence of excess unlabelled rANP(1-28) (1 microM), binding to these structures were completely displaced. Therefore, specific ANP receptors exist in the kidney, adrenal gland, stomach, intestine, oviduct, epididymis, seminiferous tubules and brain. The ANP system may be involved in physiological regulatory function in the freshwater turtle, Amyda japonica.