Isidoro Rossodivita

The dopaminergic system in hypertension.

Dopamine exerts cardiovascular and renal actions mediated through interaction with specific dopamine receptors. Dopamine receptors are cell surface receptors coupled to G-proteins and classified into two main super families based on biochemical, pharmacological and molecular characteristics. The dopamine D1-like receptor super family includes D1 and D5 receptors, known also in rodents as D1A and D1B sites. These receptors are linked to stimulation of adenylate cyclase. The dopamine D2-like receptor super family includes D2, D3 and D4 receptors. These receptors are linked to inhibition of adenylate cylase or not related with this enzyme activity. They also interfere with opening of Ca+2 channels and are linked to stimulation of K+ receptors. Dopamine receptor subtypes are expressed in brain as well as in extracerebral structures such as the heart, blood vessels, carotid body, kidney, adrenal gland, parathyroid gland and gastrointestinal tract. In the kidney, which represents the peripheral organ where dopamine receptors were more extensively investigated, dopamine receptors are involved in regulation of hemodynamic, electrolyte and water transport, as well as renin secretion. Hypertension-related dopamine receptor changes were also investigated primarily in the kidney. Defective renal dopamine production and/or dopamine receptor function have been reported in human primary hypertension as well as in genetic models of animal hypertension. There may be a primary defect in D1-like receptors and an altered signalling system in the proximal tubules that lead to reduced dopamine-mediated effects on renal sodium excretion in hypertension. Studies on the influence of hypertension on dopamine D2-like receptors are sparse Disruption of either D1A or D3 receptors at the gene level causes hypertension in mice. Using peripheral blood lymphocytes as possible markers of the status of dopamine receptors in essential hypertension, no changes of dopamine D1-like receptors were noticeable, whereas an increase of dopamine D2-like receptors likely representing an up-regulation mechanism was reported. Available information collectively indicates an involvement of peripheral dopaminergic system in hypertension consisting either in impaired receptor transduction mechanisms and/or in receptor loss. A better knowledge of molecular bases of these changes may contribute to the development of specific therapeutic approaches in the future.

Neurotrophins and Neurotrophin Receptors in Human Pulmonary Arteries

The localization of neurotrophins (NTs) and NT receptors was analyzed in sections of human extra- and intrapulmonary arteries by Western blot analysis and immunohistochemistry. In extrapulmonary branches of human pulmonary artery, NT and NT receptor immunoreactivity was located in the tunica intima, within endothelium, in the tunica media, within smooth muscle and in the tunica adventitia. In different sized intrapulmonary arteries, NT and NT receptor immunoreactivity was observed primarily in the tunica adventitia. A faint NT and NT receptor immunoreactivity was observed in the tunica media of large-sized branches of intrapulmonary arteries, but not within medium- or small-sized intrapulmonary vessels or in tunica intima of different sized intrapulmonary arteries. These findings suggest that NTs may have a role in the control of vascular responses in the pulmonary system acting as local paracrine or autocrine mediators. The possible relevance of the NT system in human pulmonary vasculature identified in this study is discussed.

AUTORADIOGRAPHIC LOCALIZATION OF DOPAMINE D2-LIKE RECEPTORS IN THE RABBIT PULMONARY VASCULAR TREE

In the present study, the pharmacological characteristics and the anatomical localization of dopamine D2-like receptor sites in the extraparenchymal and in the intraparenchymal portion of the rabbit pulmonary artery were investigated using combined radioligand binding and light microscope autoradiography with [3H]-spiroperidol (spiperone) as a ligand. The ligand was bound to sections of the pulmonary artery in a manner consistent with the labelling of dopamine D2-like receptors with an equilibrium dissociation constant (Kd) of about 2.4±0.07 nmol/l and a maximum density of binding sites of 65±4.5 fmol/mg tissue. In contrast, binding experiments made with sections of rabbit lung did not allow the evaluation of specific binding. Light microscope autoradiography showed the development of specific silver grains within the tunica adventitia of extraparenchymal branches of rabbit pulmonary artery and of large and, to a lesser extent, of medium-sized intraparenchymal branches of the pulmonary artery. No silver grains were found within small branches of the pulmonary artery or of the pulmonary vein. Development of adventitial silver grains was inhibited by compounds active at dopamine receptors. The greater sensitivity to displacement by domperidone, haloperidol, (−)-sulpiride and bromocriptine than to displacement byN-propyl-norapomorphine, quinpirole or clozapine suggests that the [3H]-spiroperidol binding sites observed in extraparenchymal, large and medium-sized branches of the pulmonary artery belong, probably, to the dopamine D2 receptor subtype. The possible pre-junctional localization of these sites is discussed.

Changes in glutathione content and localization in rat heart as a function of age.

The influence of aging on glutathione levels and distribution in the heart was studied in male Sprague-Dawley rats of 3 (young), 12 (adult) and 24 (old) months of age using biochemical and histofluorescence techniques, respectively. Biochemical assays of reduced glutathione (GSH) in the right and left ventricles and in the septum showed a significant decrease in GSH levels in adult in comparison with young animals. No further changes were noticeable between adult and old rats. GSH histofluorescence revealed a rather homogeneous distribution of the product of histochemical reaction within both right and left atria in 3-month-old rats. In 12-month-old rats a reduction of GSH histofluorescence in comparison with younger animals was noticeable. The loss is more consistent in the epicardial portion of the right atrium and in the endocardial region of the left atrium. In the atria of 24-month-old rats GSH reactivity was homogeneously distributed throughout the atrial wall and was significantly lower than in young or adult rats. In 3-month-old rats GSH histofluorescence was slightly lower in the epicardial than in the endocardial portions of both ventricles. In adult rats a significant decrease of GSH histofluorescence was noticeable in comparison with 3-month-old rats. The loss is particularly pronounced within the endocardial region of the left ventricle. In 24-month-old rats GSH histofluorescence showed no significant differences between adult rats. However, GSH was more homogeneously distributed throughout the ventricular wall than in adult animals. The significance of these data is discussed in relation to the role that GSH plays in protecting the myocytes against free radical damage.

Age-related changes of sulphide-silver staining in the rat hippocampus

The influence of ageing on sulphide-silver positive zinc stores was assessed in the stratum radiatum of the CA1-CA3 sub fields of the rat hippocampus and in the molecular layer of the dentate gyrus using a silver amplification histochemical technique associated with microdensitometry. The volume of areas examined for microdensitometry was evaluated as well by quantitative image analysis. Male Sprague-Dawley rats aged 3 months (considered to be young), 12 months (considered to be adult) and 24 months (considered to be old) were used. Microdensitometric analysis of values of sulphide-silver staining corrected for the volume of hippocampal areas investigated revealed no age-dependent changes of staining in the CA1 sub field of the hippocampus. In the CA2 sub field a decrease of sulphide-silver staining was noticeable in aged rats in comparison with younger cohorts. A progressive reduction in the intensity of sulphide-silver staining was observed in the CA3 sub field of the hippocampus. In the molecular layer of the dentate gyrus, the intensity of staining was decreased in adult and old rats in comparison with young animals. These findings indicate a different sensitivity to ageing of histochemically detectable zinc stores of rat hippocampus. The possibility of a specific sensitivity to senescence of different zinc-containing pathways of the hippocampus is discussed.

Influence of treatment with the calcium channel blocker darodipine (PY 108-068) on the morphology of pial and coronary arteries in spontaneously hypertensive rats

The present study was designed to assess the influence of treatment with the calcium channel blocker darodipine (PY 108-068) on the morphology of pial and coronary arteries in spontaneously hypertensive rats (SHR). Twelve week male SHR were used in this study. One group was treated with a daily dose of 5 mg/Kg of darodipine, while the control group of SHR was treated with placebo. Age-matched normotensive Wistar Kyoto (WKY) rats were used as a reference group. After 12 weeks of treatment the rats were sacrificed. The brains and the hearts were removed, embedded in resin, cut and used for light microscope analysis. Darodipine treatment reduced blood pressure in SHR. Morphometric analysis of different sized pial and coronary arteries revealed decreased arterial lumen in SHR in comparison with WKY rats. The area occupied by the tunica media and the media-to-lumen ratio were increased in SHR in comparison with WKY rats. In darodipine-treated rats the area occupied by the arterial lumen was increased in comparison with control SHR, whereas the area occupied by the tunica media and the media-to-lumen ratio were decreased. Pial arteries were more sensitive than coronary arteries to darodipine treatment. Medium and small sized pial and coronary arteries were most sensitive to darodipine treatment. Large-sized coronary artery branches were unaffected by pharmacological treatment. The above results suggest that treatment of SHR with darodipine is able to reduce high blood pressure and to counter the development of structural changes of pial and coronary arteries noticeable in SHR. The higher sensitivity of the cerebral vasculature to darodipine treatment is discussed.