Adrenomedullin expression and function in the rat carotid body.

Adrenomedullin (AM) immunoreactivity has been found in granules of the glomus (type I) cells of the carotid bodies in rats. The identity of these cells was ascertained by colocalization of immunoreactivities for AM and tyrosine hydroxylase in their cytoplasm. Exposure of freshly isolated carotid bodies to synthetic AM resulted in a concentration- and time-dependent degranulation of glomus cells as measured by dopamine (DA) release. DA release reached a zenith 30 min after exposure to AM (94.2% over untreated controls). At this time-point, the response to AM was similar to the one elicited by 5 min of exposure to 100 mM K+. Nevertheless, injection of 1 micro l 60 nM AM/g body weight into the tail vein of the rats did not induce statistical differences in DA release from the carotid bodies. Exposure of the oxygen-sensitive cell line PC-12 to hypoxia elicited an increase in AM mRNA expression and peptide secretion into serum-free conditioned medium. Previous data have shown that elevation of AM expression under hypoxia is mediated through hypoxia-inducible factor-1, and that exposure of chromaffin cells to AM results in degranulation. All these data suggest that AM is an important autocrine regulator of carotid body function.

Regulation of pancreatic physiology by adrenomedullin and its binding protein.

Adrenomedullin (AM) is a 52 amino acid, multifunctional hormone. It is expressed in many tissues of the human body including the pancreas, where it is mainly localized to the periphery of the islets of Langerhans and specifically to the pancreatic polypeptide-expressing cells. The AM receptor, a complex formed by calcitonin receptor-like receptor (CRLR) and receptor activity-modifying proteins (RAMPs), and the recently discovered AM-binding protein, complement factor H (fH), are expressed in the insulin-producing beta-cells. The colocalization of these key elements of the AM system in the endocrine portion of the pancreas implicates AM in the control of both normal and altered pancreatic physiologies. AM inhibits insulin secretion both in vitro (isolated rat islets) and in vivo (oral glucose tolerance test in rats) in a dose-dependent manner. The addition of fH to isolated rat islets produces a further reduction of insulin secretion in the presence of AM. Furthermore, AM is elevated in plasma from patients with pancreatic dysfunctions such as type 1 or type 2 diabetes and insulinoma. Using a diabetic model in rats, we have shown that AM increases circulating glucose levels whereas a blocking monoclonal antibody against AM has the opposite effect and improves postprandial recovery. Such experimental evidence implicates AM as a fundamental factor in maintaining insulin homeostasis and normoglycemia, and suggests the implication of AM as a possible causal agent in diabetes. Further investigation focused on the development of blocking agents for AM could result in new treatments for pancreatic AM-related disorders.

Adrenomedullin and cancer.

Adrenomedullin (AM) is a pluripotent hormone with structural similarities to calcitonin gene-related peptide (CGRP), which is expressed by many tissues in the body and shows a remarkable range of effects mediated by paracrine/autocrine and possibly endocrine mechanisms. AM has been implicated as a mediator of several pathologies such as cardiovascular and renal disorders, sepsis, inflammation, diabetes and cancer, among others. AM is expressed in a variety of tumors where it aggravates several of the molecular and physiological features of malignant cells. AM has been shown to be a mitogenic factor stimulating growth in several cancer types and to encourage a more aggressive tumor phenotype. In addition, AM is an apoptosis survival factor for cancer cells and an indirect suppressor of the immune response through its binding protein, complement factor H, and regulation in expression of cytokines. AM plays an important role in environments subjected to low oxygen tensions, which is a typical feature in the proximity of solid tumors. Under these conditions, AM is upregulated through a hypoxia-inducible factor 1 (HIF-1)-dependent pathway and acts as a potent angiogenic factor promoting neovascularization. The collective findings brought together over the last years place AM as a major regulator of carcinogenesis-tumor progression and identifies its autocrine loop as a putative target for developing new strategies against human cancers.

Localization of adrenomedullin-like immunoreactivity in the hypothalamo-hypophysial system of amphibians.

The presence of adrenomedullin-like immunoreactive (AMi) cell bodies and fibers in the hypothalamus and hypophysis of the amphibians Rana perezi (anuran) and Pleurodeles waltl (urodele) was examined by immunohistochemistry. A large population of AMi neurons was found in the suprachiasmatic nucleus of both species. Differently, AMi cells in the magnocellular nucleus of the preoptic area were only found in the urodele, whereas dispersed cells in the caudal infundibular region were exclusively present in the anuran. This different staining pattern is reflected in the hypophysis where the neural lobe is primarily immunoreactive in the urodele while the labeling in the intermediate lobe prevailed in the anuran. The results strongly suggest that, as is mammals, the AM in amphibians may play an important regulatory role in the hypothalamo-hypophysial system.

Effects of food nutrient content, insect age and stage in the feeding cycle on the FMRFamide immunoreactivity of diffuse endocrine cells in the locust gut.

We have studied the influence of variations in dietary protein and digestible carbohydrate content, of insect age and of time during the feeding cycle on the endocrine cells of the ampullar region of the midgut in the African migratory locust Locusta migratoria L. Morphometric analysis of FMRFamide-like immunoreactivity was used as an indirect measure of the amount of FMRFamide-related peptides (FaRPs) stored in the gut endocrine cells. There was a highly significant correlation between FaRP content and the nutritional quality of the food, measured relative to the concentrations and ratio of protein to digestible carbohydrate in a nutritionally optimal diet. The direction of the relationship between FaRP content and diet quality varied with age during the fifth stadium. On day 1, FaRP levels increased with the nutritional quality of the food, while on day 4 the opposite relationship was observed. Release of peptide was triggered by the onset of a meal during ad libitum feeding, with cell FaRP levels returning to premeal values within 15 min of the meal ending. The results also suggested that cell contents were released during food deprivation beyond the normal intermeal interval. Locusts switched for a single meal during ad libitum feeding on day 4 from a low- to a high-carbohydrate food did not respond by reducing endocrine cell FaRP content. Our results show a relationship between the diffuse gut endocrine system and feeding and nutrition in locusts. The ampullar endocrine cells are in three-way contact with the midgut luminal contents, with the primary urine from the Malpighian tubules and with the haemolymph. They are thus ideally positioned to play an integrative receptor-secretory function in the regulation of a variety of post-ingestive processes, such as enzyme secretion, absorption, gut motility or nutrient metabolism.

Dietary influences over proliferating cell nuclear antigen expression in the locust midgut.

We have studied the influence of variations in dietary protein (P) and digestible carbohydrate (C), the quantity of food eaten, and insect age during the fifth instar on the expression of the proliferating cell nuclear antigen (PCNA) in the epithelial cells of the midgut (with special reference to the midgut caeca) in the African migratory locust, Locusta migratoria. Densitometric analysis of PCNA-immunostained cells was used as an indirect measure of the levels of expression of PCNA, and a PCNA cellular index (PCNA-I) was obtained. Measurements of the DNA content of the cells have also been carried out by means of microdensitometry of Feulgen-stained, thick sections of midgut. A comparison between the PCNA nuclear level and the DNA content was performed. The PCNA levels were significantly different among the cells of the five regions studied: caeca, anterior ventricle, medial ventricle, posterior ventricle and ampullae of the Malpighian tubules. We have studied in more detail the region with highest PCNA-I, i.e. the caeca. The quality and the quantity of food eaten under ad libitum conditions were highly correlated with both the PCNA and DNA levels in the caeca cells. Locusts fed a diet with a close to optimal P:C content (P 21%, C 21%) showed the highest PCNA and DNA content. In locusts fed a food that also contained a 1:1 ratio of P to C but was diluted three-fold by addition of indigestible cellulose (P 7%, C 7%), a compensatory increase in consumption was critical to maintaining PCNA levels. Our measurements also showed that the nuclear DNA content of the mature and differentiated epithelial cells was several-fold higher than the levels in the undifferentiated stem cells of the regenerative nests. These results, combined with the low number of mitotic figures found in the regenerative nests of the caeca and the marked variation in PCNA levels among groups, suggest that some type of DNA endoreduplication process may be taking place. Our data also indicate that the DNA synthetic activity in the midgut is related to feeding in locusts. The possible dietary and nutritional regulatory mechanisms and the significance of the differences found are discussed.

Impaired intestinal sugar transport in cirrhotic rats: correction by low doses of insulin-like growth factor I.

BACKGROUND & AIMS: Malnutrition is a complication of liver cirrhosis accompanied by reduced insulin-like growth factor I (IGF-I) availability. The aim of this study was to analyze the effect of IGF-I on intestinal D-galactose absorption in cirrhotic rats. METHODS: IGF-I (2 micrograms.100 g body wt-1.day-1) or saline were given for 14 days to rats in whom cirrhosis was induced with CCl4. Galactose transport and sodium-glucose/galactose-ligand transporter 1 (SGLT-1) expression were assessed in jejunal rings and in brush border membrane vesicles (BBMVs). RESULTS: Compared with that in controls, galactose transport in everted jejunal rings was significantly reduced in cirrhotic rats but showed normal values after IGF-I treatment. The kinetic study of D-galactose uptake by BBMVs showed decreased maximal velocity (Vmax) and diminished transporter affinity in cirrhotic rats. These kinetic parameters reverted to normal after IGF-I treatment. Microvilli were significantly elongated in cirrhotic rats but of normal size in the IGF-I-treated group. The expression of SGLT-1 on BBMVs (Western blot) and on the luminal membrane of enterocytes (immunohistochemistry) was not reduced in cirrhotic animals compared with controls or IGF-treated cirrhotic rats. CONCLUSIONS: Intestinal sugar transport is disturbed in experimental cirrhosis, and this alteration is corrected by IGF-I.