Presence of renin in the glomerular and aglomerular kidney of marine teleosts

Renin-angiotensin system in vertebrates: phylogenetic view of structure and function

Renin substrate, biological renin activity, and/or renin-secreting cells in kidneys evolved at an early stage of vertebrate phylogeny. Angiotensin (Ang) I and II molecules have been identified biochemically in representative species of all vertebrate classes, although variation occurs in amino acids at positions 1, 5, and 9 of Ang I. Variations have also evolved in amino acid positions 3 and 4 in some cartilaginous fish. Angiotensin receptors, AT₁ and AT₂ homologues, have been identified molecularly or characterized pharmacologically in nonmammalian vertebrates. Also, various forms of angiotensins that bypass the traditional renin-angiotensin system (RAS) cascades or those from large peptide substrates, particularly in tissues, are present. Nonetheless, the phylogenetically important functions of RAS are to maintain blood pressure/blood volume homeostasis and ion-fluid balance via the kidney and central mechanisms. Stimulation of cell growth and vascularization, possibly via paracrine action of angiotensins, and the molecular biology of RAS and its receptors have been intensive research foci. This review provides an overview of: (1) the phylogenetic appearance, structure, and biochemistry of the RAS cascade; (2) the properties of angiotensin receptors from comparative viewpoints; and (3) the functions and regulation of the RAS in nonmammalian vertebrates. Discussions focus on the most fundamental functions of the RAS that have been conserved throughout phylogenetic advancement, as well as on their physiological implications and significance. Examining the biological history of RAS will help us analyze the complex RAS systems of mammals. Furthermore, suitable models for answering specific questions are often found in more primitive animals.

Distribution of NGF and NT-3-like protein immunoreactivity in the teleost kidney

By means of immunochemistry and immunohistochemistry, we investigated in the kidney of freshwater and marine teleostean species for the presence and localization of three neurotrophins: nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin (NT)-3. In both species studied, NGF-like and NT-3-like immunoreactivity were present in the kidney with different distribution patterns, while BDNF-like immunoreactivity was never detected. In goldfish, NGF-like and NT-3-like immunoreactivity were identified extensively in cells along part of the arterial branches adjacent to the afferent arterioles. In scorpion fish, NGF-like and NT-3-like immunoreactive cells were observed both on afferent arterioles and on adjacent secondary branches derived from renal arteries. No immunoreactivity was detected in other renal structures. A staining pattern of immunoreactivity similar to that obtained for NGF and NT-3 was detected utilizing S100 antibody as a juxtaglomerular (JG) cell marker. Double immunolabellings NGF/S100 and NT-3/S100 evidenced the coexistence of neurotrophin-like proteins and S100-like protein in the same immunoreactive cells, thus identifying them as juxtaglomerular cells. Western blot analysis revealed the presence of molecules immunoreactive to NGF and NT-3, whose molecular weights were very similar to those of the corresponding mammalian neurotrophins. These findings extend the presence and distribution of NGF-like and NT-3-like IR in the kidney to teleost species, suggesting a probable participation of these proteins in the renal functions of freshwater and marine teleosts.

The pressor response to exogenous angiotensin I and its blockade by angiotensin II analogues in the American alligator

We examined the pressor response to exogenous, nonnative angiotensin I (ANG I; bullfrog, turtle, and fowl) in the conscious American alligator, Alligator mississippiensis. In addition, the inhibitory effects of three ANG II analogues ([Sar1, Ala8], [Sar1, Thr8], and [Sar1, Ile8]ANG II) on the pressor responses to angiotensin I (fowl ANG I, [Asp1, Val5, Ser9]) were also examined. Intravenous administration of bullfrog, turtle, and fowl ANG I at 0.1, 0.5, and 1.0 micrograms/kg produced dose-dependent increases in arterial blood pressure. [Val5]ANG II at 0.05, 0.1, and 0.5 micrograms/kg, or NE at 2 micrograms/kg also produced dose-dependent increases in blood pressure. [Sar1, Ile8]ANG II and [Sar1, Ala8]ANG II (10 micrograms/kg/min) both attenuated the pressor response to fowl ANG I whereas [Sar1, Thr8]ANG II (10 micrograms/kg/min) produced no significant blockade. These data demonstrate: (1) All three exogenous ANG I molecules exert potent vasopressor responses in the alligator, (2) [Sar1, Ile8]ANG II is the most effective ANG antagonist, and (3) the alligator appears to possess a renin-angiotensin system similar to that found in other vertebrates.

The granular epithelioid cells in the kidney of the lemon sole (Pleuronectes microcephalus Donovani)

Serial sections from kidneys of 5 aglomerular lemon soles (Pleuronectes microcephalus) demonstrated the presence of anastomosing arteriolar networks in the caudal half of the organs. There was no preferred location of the networks, which were found both near the surface and in the deeper parts of the kidney. The size of the networks varied; the largest measured more than 900 micrometers in the longest axis and covered an area larger than 500,000 micrometers2, whereas the smallest measured about 60 micrometers in diameter with an area of 2040 micrometers2. The larger networks were invariably located close to large intrarenal veins. Anastomoses were found between the arteriolar networks and the peritubular capillaries and also associated with veins. The walls of the arterioles were composed of granulated epithelioid cells, exhibiting numerous intracytoplasmic granules. These granules occasionally had a rod-like appearance with a paracrystalline substructure. Using antibodies directed against murine and human renin, the epithelioid cells in the walls of the arteriolar networks and the cytoplasmic granules revealed a positive immunoreaction. The results suggest that the renin-angiotensin system in the aglomerular lemon sole may be important for both the regulation of the systemic blood pressure and the blood supply to the peritubular capillaries of the kidney.

Gastric acid secretion and water balance in the marine teleost Gadus morhua

Gastric acid secretion was measured in unanaesthetized codfish surgically equipped with a catheter draining the stomach. The pylorus was ligated. Without perfusion of the intestine, or during perfusion with pure sea water (100% SW) or slightly diluted (67%) SW, gastric acid secretion was low ( less than 10 mumol H+/kg.h) and the fishes became dehydrated during the experiment. Perfusion of the intestine with 50% or 3% SW enabled the fishes to compensate for the water loss to the environment and greatly enhanced gastric acid secretion. Acid secretion was elevated also in fishes in which the dehydration was prevented by an intra-muscular infusion of saline. Perfusion of the intestine (8.5 ml/h) decreased the hourly effluent volume ('drinking rate') from the stomach to almost zero within 2 h. The effect was independent of the degree of dilution of the perfusing SW, but was less pronounced when the perfusion rate was lowered. Intra-muscular saline also depressed 'drinking rate'. The acid secretion prevailing during perfusion of the intestine with SW at a dilution preventing dehydration--suggested to represent the basal acid secretion of the codfish--was inhibited by atropine, hexamethonium, and metiamide.