[Aluminum absorption in the presence of normal kidney function: the effect of the pH]. / Absorción de aluminio en presencia de función renal normal: efecto del pH.

Aluminium is a toxic metal of known importance in patients with chronic renal failure on hemodialysis, with a gastrointestinal absorption modulated by several factors including gastric pH which modifies the solubility of Aluminium hydroxide and can increase its absorption. We studied twenty six patients with normal renal function: control (n = 13); presurgery (n = 8); postsurgery (n = 5) by an aluminium hydroxide absorption test (30 mg/kg); serum and urinary aluminium was determined as well as gastric pH and hematologic parameters at different time periods. It was observed that presurgery ulcer patients (pH mean = 2.09) increased serum and urine aluminium levels as well as aluminium/creatinine ratio in urine after the test, opposite to what occurs in the postsurgery group (pH mean = 5.78) in which such parameters were not significantly modified. No differences were found in hematological parameters between the two groups. Our results indicate that acid gastric pH seems to be a factor capable of increasing gastrointestinal absorption of aluminium hydroxide since its solubility and thus its disponibility is increased, and make a point on the risk of a prolonged administration of antacids containing aluminium in patients with normal renal function.

Proopiomelanocortin (POMC)-related peptides in the brain of the rainbow trout, Salmo gairdneri.

We have investigated the presence of ACTH, alpha-MSH and beta-endorphin, three peptides which derive from the multifunctional precursor protein proopiomelanocortin (POMC) in the brain of the rainbow trout Salmo gairdneri. Using both the indirect immunofluorescence and peroxidase-antiperoxidase techniques, a discrete group of positive cells was identified in the hypothalamus, within the anterior part of the nucleus lateralis tuberis. alpha-MSH-containing neurons represented the most abundant immunoreactive subpopulation. Coexistence of alpha-MSH, ACTH and beta-endorphin was observed in the lateral part of the nucleus. ACTH- and beta-endorphin-containing cells were mainly distributed in the rostral and caudal regions of the nucleus. In the medial portion of the nucleus lateralis tuberis, numerous cells were only stained for alpha-MSH. Moderate to dense plexuses of immunoreactive fibers were observed in the ventral thalamus and the floor of the hypothalamus. Some of these fibers projected towards the pituitary. The concentrations of ACTH, alpha-MSH and beta-endorphin-like immunoreactivities were measured in microdissected brain regions by means of specific radioimmunoassays. Diencephalon, mesencephalon and medulla oblongata extracts gave dilution curves which were parallel to standard curves. The highest concentrations of POMC-derived peptides were found in the diencephalon (alpha-MSH: 4.28 +/- 0.43 ng/mg prot.; ACTH: 1.08 +/- 0.09 ng/mg prot.; beta-endorphin: 1.02 +/- 0.1 ng/mg prot.), while lower concentrations were detected in the mesencephalon, medulla oblongata and telencephalon. The present results demonstrate that various peptides derived from POMC coexist within the same cell bodies of the fish hypothalamus. Taken together, these data suggest that expression and processing of POMC in the fish brain is similar to that occurring in pituitary melanotrophs.

Melanin-concentrating hormone (MCH) immunoreactivity in the brain and pituitary of the dogfish Scyliorhinus canicula. Colocalization with alpha-melanocyte-stimulating hormone (alpha-MSH) in hypothalamic neurons.

The distribution of melanin-concentrating hormone (MCH) in the central nervous system of the dogfish Scyliorhinus canicula was determined by indirect immunofluorescence and peroxidase-anti-peroxidase techniques, using an antiserum raised against synthetic salmon MCH. Three groups of MCH-positive cell bodies were localized in the posterior hypothalamus. The most prominent cell group was detected in the nucleus sacci vasculosi. Scattered MCH-immunoreactive cells were observed in the nucleus tuberculi posterioris and in the nucleus lateralis tuberis. At the pituitary level, the caudal part of the median lobe of the pars distalis contained strongly MCH-positive perikarya. Some of these cells were liquor-contacting-type. Immunoreactive fibers originating from the hypothalamic perikarya projected throughout the dorsal wall of the posterior hypothalamus. Positive fibers were also detected within the thalamus and the central gray of the mesencephalon. The distribution of MCH-containing neurons was compared to that of alpha-MSH-immunoreactive elements using consecutive, 5-micron thick sections. Both MCH- and alpha-MSH-immunoreactive peptides were found in the same neurons of the nucleus sacci vasculosi. These data suggest that MCH and alpha-MSH, two neuropeptides which exert antagonistic activities on skin melanophores, may also act in a coordinate manner in the central nervous system of cartilaginous fish.

Immunocytochemical Localization and Biochemical Characterization of alpha-Melanocyte-Stimulating Hormon in the Brain of the Rainbow Trout, Salmo gairdneri.

Abstract The distribution of alpha-melanocyte-stimulating hormone (alpha-MSH)-like immunoreactivity in the central nervous system of the rainbow trout Salmo gairdneri was investigated by indirect immunofluorescence and peroxidase-antiperoxidase techniques, using a highly specific antiserum generated in rabbits against synthetic alpha-MSH. Immunoreactive perikarya were exclusively observed in the basal hypothalamus within the pars anterioris of the nucleus lateralis tuberis. In this region, a moderate number of small stained cell bodies were observed surrounding the dorsal wall of the anterior infundibular recess. These immunoreactive cells were organized in rostro-caudal rows extending over the whole portion of the nucleus. Positive fibres originating from these perikarya were visualized in the dorsal posterior lobe and the ventral hypothalamus. A dense tract of immunoreactive fibres projected ventrally through the pituitary stalk and terminated in the neurohypophysis. The concentrations of alpha-MSH in different regions of the brain were measured by means of a sensitive and specific radioimmunoassay. The dilution curves obtained with synthetic alpha-MSH and serial dilutions of diencephalon, mesencephalon, medulla oblongata, telencephalon or pituitary extracts were strictly parallel. The highest concentration of alpha-MSH in brain was found in the diencephalon (1.31 +/- 0.07 ng/mg protein). In contrast alpha-MSH was not detectable in cerebellar extracts. Reverse-phase high-performance liquid chromatography and radioimmunoassay were used to characterize alpha-MSH-like peptides in the trout brain and pituitary. Two major forms of immunoreactive alpha-MSH were resolved by high performance liquid chromatography in hypothalamic extracts; these peptides exhibited the same retention times as des-Na-acetyl alpha-MSH and its sulfoxide derivative, respectively. Additional peaks of alpha-MSH immunoreactive material were detected in pituitary extract. These latter peptides coeluted with authentic alpha-MSH, diacetyl alpha-MSH and their sulfoxide forms. These results provide the first evidence for the presence of alpha-MSH in the brain of a teleostean fish. Our data indicate that, in the brain, the immunoreactivity corresponds to the non-acetylated form of alpha-MSH, while three different types of alpha-MSH-like molecules (namely deacetylated, monoacetylated, and diacetylated forms) coexist in the pituitary. It thus appears that, in salmonoid fish, mono- or diacetylation of the N-terminal serine residue of aL-MSH only occurs at the pituitary level.

Sauvagine/urotensin I-like immunoreactivity in the brain of the dogfish, Scyliorhinus canicula.

The localization of a sauvagine (SV)/urotensin I (UI)-like material in the brain of the dogfish, Scyliorhinus canicula, was studied by immunohistochemical techniques, employing an antiserum raised in rabbit against synthetic SV which widely cross-reacts with UI. Positive cell bodies and nerve fibers were identified in the dorsocaudal hypothalamic region of the tuberculum posterius, in the nucleus sacci vasculosi and nucleus tuberculi posterioris. A dense network of immunoreactive axons was shown in the whole tuberculum posterius. These findings support the view that SV/UI-like peptides may be involved in neuromodulatory functions throughout the brain of cartilaginous fish.

Neuronal localization of immunoreactive adrenocorticotropin-like substance in the hypothalamus of elasmobranch fishes.

The occurrence and localization of adrenocorticotropin (ACTH)-like material in the brain of two species of elasmobranch fishes, Scyliorhinus canicula and Squalus acanthias, were studied by immunohistochemical techniques using an antiserum generated against human ACTH1-24. In both species immunopositive neurons and fibers were recognized in the basal hypothalamus mainly distributed in the nucleus lateralis tuberis, in which many of these elements were of the liquor-contacting type. A few ACTH-like positive cells were also found in the nucleus lobi lateralis hypothalami. The features of this peptidergic system, its topographic distribution to form intrinsic circuits within the posterior hypothalamic area and probably connections with the pituitary, suggest implications in brain neuromodulatory activities and hypophyseal regulation for this peptide.