Biomedical subjects

F Amenta

Publications and source records attributed to F Amenta.

At least 181 records · Page 10Linked to original sources

PubMed1991

Autoradiographic localization of beta-adrenergic receptors in human large coronary arteries.

The distribution of beta-adrenergic receptors in sections of the human right and left coronary arteries and of the anterior intraventricular branch was studied by the use of combined in vitro radioreceptor binding and autoradiographic techniques. [125I]Cyanopindolol was used as a ligand for beta-adrenergic receptors. Binding of the radioligand to sections of the three coronary arteries under study was saturable, stereoselective, reversible, and displaceable by antagonists and agonists with the rank order of potency expected for beta-adrenergic receptors. Analysis of binding isotherms indicated maximum binding capacities of 41.5 fmol/mg protein for the right coronary artery, 35.4 fmol/mg protein for the left coronary artery, and 25.7 fmol/mg protein for the anterior interventricular branch. Dissociation constants were approximately 35 pM in the arteries examined. The relative amounts of beta 1- and beta 2-receptor subtypes were as follows: 72% beta 1-receptors and 28% beta 2-receptors in the right coronary artery; 65% beta 1-receptors and 35% beta 2-receptors in the left coronary artery; 40% beta 1-receptors and 60% beta 2-receptors in the anterior interventricular branch. The results of autoradiographic analysis revealed a predominance of beta 1-receptors in the medial layer. beta 2-Receptors were localized primarily in the adventitia, in the adventitia-media border, and in the intimal layer. These results should lead to a better understanding of the mechanisms involved in the control of coronary circulation in humans.

Adolescent↗

PubMed1991

Renal dopamine and changes in dopamine receptor ligand binding during high sodium intake.

This study was designed to measure changes in plasma levels of atrial natriuretic peptides (ANP), urine volume (UV), urinary excretion of dopamine (UDAV) and sodium (UNaV), and dopamine (DA) receptor affinity (Kd) and binding sites (Bmax) in kidneys of rats drinking normal saline for a period of 7 days. The saline intake significantly increased UV, UNaV, plasma ANP, UDAV, and its primary metabolite dihydroxyphenyl acetic acid (DOPAC) for the period of 7 days. Bmax increased significantly 1 day after the initiation of saline intake, however, the increase appeared to be transient since measurements of Bmax made after 7 days of saline intake were not significantly different from the control group. No changes in Kd were observed. These results indicate that renal DA contributes to maintenance of Na balance during increased Na intake and that renal DA receptors undergo transient changes during this period.

Animals↗

PubMed1991

Presence of catecholamine-related enzymes in a subpopulation of primary sensory neurons in dorsal root ganglia of the rat.

The presence of enzymes (tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (D beta H)) and enzymatic activities (monoamino oxidase, (MAO)) related to catecholamine synthesis and degradation have been investigated in cervical, thoracic and lumbar dorsal root ganglia (DRG) of adult male rats using immunohistochemical and enzyme histochemical techniques, respectively. A small population (between 2-4%) of TH-like immunoreactive and MAO positive neurons was found. They were small in diameter (18 +/- 2 microns), predominate in lumbar DRG and did not display D beta H-like immunoreactivity. These sensory neurons which are likely catecholaminergic were insensitive to systemic administration of capsaicin and 6-hydroxydopamine. Colchicine administration caused an increase of TH-like immunoreactivity and MAO activity. Pargyline produced an increase in TH-like immunoreactivity and the disappearance of MAO activity. The possible dopaminergic nature of the subpopulation of DRG sensory neurons investigated in the present study is discussed.

Animals↗

PubMed1991

Effect of long-term isradipine treatment on the hypertension-dependent changes in coronary arteries in spontaneously hypertensive rats.

The present study was designed to assess the effect of long-term isradipine treatment on the morphology of different-sized coronary artery branches in spontaneously hypertensive rats (SHR). Male SHR (12-week-old) received 1 mg/kg/day isradipine or vehicle (control group) orally for 12 weeks. Age-matched normotensive Wistar-Kyoto (WKY) rats were used as a reference group and did not receive any treatment. The animals were perfused with a fixative solution through the left ventricle and left ventricle blocks were embedded in resin. Sections including different-sized coronary artery branches were examined under a light microscope connected with an image analyser. The area occupied by the medial layer and the wall-to-lumen ratio were assessed in coronary artery branches of small (diameter less than 100 microns), medium (diameter 100-250 microns) and large (diameter greater than 250 microns) size. In control SHR, the blood pressure values and morphometric parameters examined significantly increased (p less than 0.001) in comparison with normotensive WKY rats. Isradipine treatment normalized blood pressure values in SHR and significantly reduced the area occupied by the medial layer and the wall-to-lumen ratio in small and medium-sized, but not in large-sized, coronary artery branches. These results indicate that isradipine treatment is able not only to reduce blood pressure elevation in SHR, but also to counteract the hypertension-dependent changes in the morphology of arterial branches controlling coronary resistances.

Animals↗

PubMed1990

The noradrenergic innervation of the ovary in old rats.

The influence of ageing on the noradrenergic innervation of the ovary was studied in female Wistar rats using high pressure liquid chromatography (HPLC) with electrochemical detection and catecholamine histofluorescence techniques. Old age was accompanied by a significant decrease in ovarian noradrenaline levels. In young animals (3-month-old) noradrenergic nerve fibres were distributed primarily to blood vessels and in lesser amounts to the interstitial glands. In aged animals (24-month-old) perivascular noradrenergic fibres were reduced by more than 40%; interstitial gland nerve fibres were reduced by approximately 20%. The possibility that impaired noradrenergic ovarian innervation occurring in old age may be in some way related with age-dependent failure in reproductive activity is discussed.

Aging↗

PubMed1990

Age-related changes of dopamine sensitive cyclic AMP generation in the rat frontal cortex.

The dopamine (DA) D-1 and D-2 receptors coupled to 3',5'-cyclic adenosine monophosphate (cAMP) generation were studied in membrane particles of the frontal cortex in young (3-month-old), adult (12-month-old) and aged (24-month-old) male Sprague-Dawley rats. Activation of D-1 receptors with DA, apomorphine or fenoldopam enhanced accumulation of cAMP in the frontal cortex of young rats. The stimulatory effect elicited by DA on cAMP generation declined by about 20% in adult rats. No further decline in cAMP accumulation was noticeable in aged animals. The response to dopaminergic agonists was blocked by the D-1 receptor antagonist SCH 29390 in the three age groups examined. The presence of D-2 receptors, negatively coupled to cAMP generation, was demonstrated by incubating frontal cortex membrane particles with SCH 23390 and then with DA. This inhibitory response, was also elicited with D-2 receptor agonists quinpirole or bromocriptine in the absence of SCH 23390 in which these compounds produced a decrease in cAMP. The decrease in cAMP caused following D-2 receptor stimulation was shown to be enhanced with age. No difference was observed between the three age groups of animals in the activation of cAMP production by forskolin. The present data suggest a selective decrease in the coupling between the D-1 receptor and cAMP generation in the frontal cortex of adult and aged rats and of an age-dependent increase in the coupling between the D-2 receptor and cAMP inhibition. The functional consequences of these biochemical changes may have important implications in the aging of the rat frontal cortex.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1990

Age-related changes in adrenaline content of rat splanchnic blood vessels.

The influence of ageing on the adrenaline content of the superior mesenteric artery and vein, renal artery and vein and portal vein was studied in 3-month- (young), 12-month- (adult) and 24-month-old (old) male Wistar rats using radioenzymatic assay for the measurement of catecholamine levels. Adrenaline concentrations were unchanged in the vascular wall of the blood vessels examined in adult rats, but were significantly decreased in the vascular wall of the superior mesenteric, renal and portal veins of old rats. In contrast, no age-dependent changes of adrenaline levels were found in the vascular wall of the superior mesenteric or renal arteries. The possibility that the loss of adrenaline concentrations in the venous vascular wall may be in some way related to the cardiovascular impairment occurring with age is discussed.

Aging↗

PubMed1990

Autoradiographic localization of [3H]muscimol binding sites in rat stomach: evidence for mucosal GABAA receptors.

The distribution in the rat stomach of specific [3H]muscimol binding sites, which show characteristics of GABAA receptors, was examined by light microscopic autoradiography. Silver grains representing specific binding were present both in the antrum and body, with highest densities in the muscle layers. A small fraction of the binding was confined to gland cells of the mucosa in the gastric body, rather than in the antrum. The label was not specifically concentrated at the myenteric ganglia. These findings, along with earlier data, suggests that the local GABA content may regulate not only the contractility, but also the secretory functions of the stomach via gastric GABAA receptors.

Animals↗

PubMed1990

Demonstration of dopamine DA-1 receptor sites in rat juxtaglomerular cells by light microscope autoradiography.

The binding of the selective DA-1 receptor antagonist [3H]-SCH 23390 in sections of rat kidney was studied using combined in vitro biochemical radio-receptor assay and autoradiography. [3H]-SCH 23390 was bound to sections of rat kidney in a manner consistent with the labeling of DA-1 receptors with a dissociation constant value of 4.2 nmol/l and a Bmax value of 180.6 fmol/mg protein. Light microscope autoradiography revealed a dense accumulation of silver grains in juxtaglomerular cells and in proximal convoluted tubule cells. These findings suggest that the stimulation of renin release elicited by dopamine and DA-1 receptor agonists may be mediated by the activation of DA-1 receptors located on juxtaglomerular cells.

Animals↗

PubMed1990

Age-dependent changes of the sympathetic innervation of the rat kidney.

The influence of aging on the sympathetic innervation of the kidney was studied in 3- (considered to be young), 12- (considered to be adult) and 24- (considered to be old) month-old male Sprague-Dawley rats by means of high pressure liquid chromatography with electrochemical detection, catecholamine histofluorescence and acetylcholinesterase (AChE) histochemistry. Body and kidney weights were significantly increased in adult in comparison with young rats. No further increase of either body or kidney weight was appreciated in old rats. Noradrenaline levels were increased by about 48% in adult rats and were decreased in old rats (by approx. 22% vs. young and 60% vs. adult). The density of perivascular noradrenergic fibres was significantly increased in adult rats and decreased in old animals. The percentage of kidney glomeruli supplied by AChE-positive nerve fibres is also remarkably increased in 12-month old rats and decreased in 24-month-old rats. The present data indicate that there is a striking increase in the expression of sympathetic innervation of rat kidney at 12 months of age followed by a significant decrease in the expression of innervation in old age. These changes are discussed in relation to the age-dependent impairment of renal function.

Acetylcholinesterase↗

PubMed1990

Dopamine modulation of pathological human chromaffin tissue.

To evaluate the presence of dopamine-2(DA2) binding sites in pheochromocytoma tissue, we performed binding studies and light microscopy autoradiography on sections of 7 different tumors. 3-H-Spiroperidol, a DA2 ligand, bound specifically to tumor sections with a (mean +/- SD) Kd value of 1.93 +/- 0.62 nmol/L. Binding site density (Bmax) was 29.16 +/- 2.33 fmol/mg tissue. Light microscopy autoradiography showed a nonhomogenous localization of silver grains within chromaffin cells. The specific binding was about 50% of total. To investigate whether DA2 binding sites found on pheochromocytoma cells might modulate catecholamine (CA) release, we studied the effects of oral bromocriptine (2.5 mg) on circulating CA of 5 patients with pheochromocytoma. In these patients bromocriptine caused a decrease in blood pressure (P less than .05) but no significant change in plasma CA. Our study shows the presence of DA2 binding sites on tumoral chromaffin tissue. As bromocriptine, a DA2 receptor agonist, was not able to modify tumor CA secretion, the functional role, if any, played by these binding sites on tumor secretion is still to be clarified.

Adrenal Gland Neoplasms↗

PubMed1990

Autoradiographic localization of vascular dopamine receptors.

By using combined in vitro radioreceptor binding and autoradiographic techniques, the pharmacological profile and the anatomical localization of dopamine-1 (DA-1) and dopamine-2 (DA-2) receptors were assessed in rat cerebral, mesenteric and renal arteries. 3H-SCH 23390 (DA-1 ligand) was bound by the medial layer of cerebral, mesenteric and renal arteries without different density in large, medium and small sized arteries. Moreover, 3H-SCH 23390 binding sites were not sensitive to chemical sympathectomy, suggesting postjunctional localization of DA-1 receptors. 3H-Spiroperidol (DA-2 ligand) was bound primarily by the adventitial, the adventitial-medial border as well as by the intimal layer of cerebral, mesenteric and renal arteries. The accumulation of adventitial and adventitial-medial 3H-spiroperidol binding sites was higher in medium and small sized arteries than in large ones and was remarkably reduced after chemical sympathectomy. These results show prejunctional localization of DA-2 receptors and further suggest that some DA-2 binding sites are located in the arterial intima.

Animals↗

PubMed1990

Autoradiographic localization of dopamine DA-1 receptors in the rat renal vasculature using [3H]-SCH 23390 as a ligand.

1. The localization of the selective dopamine (DA) DA-1 receptor antagonist [3H]-SCH 23390 was studied in sections of rat kidney using combined radioreceptor binding and autoradiographic techniques to identify the target of DA-1 receptors in renal vasculature. 2. Binding data were consistent with the labelling by [3H]-SCH 23390 of a single population of high affinity DA-1 sites. The apparent dissociation constant value (Kd) was 4.2 nM and the maximum binding capacity value (Bmax) was 140.6 +/- 6.5 fmol mg-1 tissue. Selective DA-1 or mixed DA-1 and DA-2 receptor antagonists or agonists were able to antagonize dose-dependently [3H]-SCH 23390 binding to sections of rat kidney. DA-2 receptor selective antagonists were ineffective. 3. Light microscope autoradiography using sections exposed to nuclear emulsion for 2 weeks revealed development of specific silver grains only within proximal cortical tubules. Longer exposure times (10 weeks) caused the development of specific silver grains in proximal and distal cortical tubules and in the medial layer of intrarenal arteries. 4. Quantitative analysis of the density of silver grains within the cortical tubules and the medial layer of intrarenal arteries revealed a significantly higher density of binding sites in proximal cortical tubules than in the vasculature or in distal cortical tubules. No significant differences in the density of silver grains in the medial layer of interlobar arcuate or cortical radial arteries were observed. 5. These results suggest that, using adequate ligand concentrations and exposure times for autoradiography, both tubular and vascular DA-1 receptors can be visualized in the rat kidney. The observation of a higher density of proximal tubules DA-1 receptors is consistent with the hypothesis of a more important role of DA-1 receptors in the control of natriuresis than of renal haemodynamics.

Animals↗

PubMed1990

Density and distribution of dopamine receptors in the cardiovascular system and in the kidney.

1. The pharmacological characteristics and the anatomical localization of dopamine (DA) DA-1 and DA-2 receptor sites were analysed in sections of rat heart, kidney, cerebral, mesenteric and caudal arteries. Moreover, DA-1 receptors were characterized in sections of human kidney. 2. [3H]-SCH 23390, used as a ligand of DA-1 receptors, was specifically bound to sections of cerebral and mesenteric arteries and to both rat and human kidney. Negligible amounts of specific binding were noticeable in the heart and in the caudal artery. The binding was consistent with the labelling of DA-1 sites. In rat tissues binding was not sensitive to 6-hydroxydopamine (6-OHDA) sympathectomy. 3. Anatomically [3H]-SCH 23390 was bound by the medial layer of cerebral, mesenteric and renal arteries. In the renal cortex, where occurred the highest accumulation of [3H]-SCH 23390 binding sites, the ligand was bound primarily by proximal convoluted cortical tubules and juxtaglomerular cells. Comparatively, the human kidney was richer in tubular binding sites than the rat kidney. The opposite is true for vascular sites. 4. [3H]-spiroperidol was used as a ligand of DA-2 receptors. To the incubation medium containing the ligand, appropriate concentrations of ketanserin were added to block the possible binding to 5-HT-2 sites. [3H]-spiroperidol was bound by sections of the structures examined in a manner consistent with the labelling of DA-2 sites. 6-OHDA caused a significant reduction in the density of cardiac and vascular [3H]-spiroperidol binding sites. 5. In the heart [3H]-spiroperidol was bound primarily by atria (6-OHDA sensitive binding).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Predominant epithelial localization of type A gamma-aminobutyric acid receptor sites within rat seminal vesicles and prostate glands.

In order to understand the role of the gamma-aminobutyric acid (GABA)-ergic system in the reproductive organs of the male, the biochemical characteristics and the autoradiographic localization of GABA type A (GABAA) receptor sites were studied in sections of the rat epididymis, seminal vesicles and prostate gland (lateral lobe) using 3H-muscimol as a ligand. No specific 3H-muscimol binding occurred in the epididymis. 3H-muscimol was bound to sections of seminal vesicles and prostate glands in a manner consistent with the labeling of specific GABAA receptors. Binding was saturable, reversible, with Kd values of 27.5 +/- 2.0 and 26.0 +/- 1.9 nmol/l and Bmax values of 230 +/- 21 and 160 +/- 13 fmol/mg protein for seminal vesicles and prostate glands, respectively. The rank order of potency of GABAergic drugs in inhibiting 3H-muscimol binding to sections of seminal vesicles and prostate glands was also consistent with the labeling of GABAA receptors. Autoradiography demonstrated the predominant accumulation of silver grains in the epithelium of seminal vesicles and prostatic glandular tissue. These findings further support the suggestion of a possible role of GABA in the male reproductive function. The predominant epithelial localization of GABAA receptors in the seminal vesicles and in the prostate gland allows us to hypothesize that GABA may be involved in the secretory activities of these glands.

Animals↗

PubMed1990

Absence of right-left asymmetries in the rat hippocampus as demonstrated by Timm staining.

Although biochemical and behavioural studies have shown right-left differences in several areas of the rat limbic system, some anatomical studies reported no significant right-left differences in several morphological parameters of the hippocampus. The purpose of the present study was to determine whether there are asymmetries in the micro-anatomy of the rat hippocampus by examining the intensity of Timm staining in various hippocampal fields and the area occupied by mossy fibres by the use of combined microdensitometric and quantitative image analysis techniques. Timm staining demonstrates the distribution of intrahippocampal association pathways because it is a histochemical marker of zinc and other heavy transition metals. There were no right-left differences in the density of Timm staining at the level of the dentate gyrus, in the dendritic layer of CA1 and CA2 fields, in the mossy fibre area or in the subiculum. These findings provide further evidence of a lack of morphological asymmetry in the rat hippocampus.

Animals↗

PubMed1990

Autoradiographic localization of dopamine DA-2 receptor sites in rat mesenteric vascular tree.

By using combined in vitro radioreceptor binding and autoradiographic techniques and [3H]spiroperidol (in the presence of the 5-hydroxytryptamine-2 receptor blocker ketanserin) as a ligand, the pharmacological properties and the anatomical localization of dopamine (DA) DA-2 receptors sites in rat mesenteric vascular tree were analyzed. [3H]Spiroperidol was bound by sections of rat mesentery in a manner consistent with the labeling of DA-2 receptors, with a Kd value of 2.48 nM and with a maximum binding value of 159 fmol/mg of protein. Light microscopic autoradiography revealed specific [3H]spiroperidol binding sites primarily in the adventitial layer and in the adventitial-medial border as well as in the intimal layer. Adventitial and adventitial-medial binding sites disappeared after 6-hydroxydopamine sympathectomy. In contrast, chemical sympathectomy was without effect on intimal [3H]spiroperidol binding sites. The density of adventitial and adventitial-medial binding sites was higher in medium and small sized vessels than in larger ones. These findings are indicative of the existence of DA-2 receptors sites located both prejunctionally (6-hydroxydopamine-sensitive) and in the intimal layer. Prejunctional mesenteric DA-2 receptors may be involved in the inhibition of noradrenaline release from sympathetic neuroeffector junctions. The functional significance of intimal [3H]spiroperidol binding sites, if any, should be established in future studies.

Animals↗

PubMed1990

Pharmacological characterization of rat renal medulla dopamine-sensitive cyclic adenosine monophosphate generating system.

The dopamine (DA) DA-1 and DA-2 receptors coupled to 3'-5'-cyclic adenosine monophosphate (cAMP) generating system were characterized in membrane particles of the rat kidney medulla. In confirmation of reports using central and other peripheral tissues, activation of DA-1 receptors with DA, apomorphine or SKF 82526 induced accumulation of cAMP. This effect was blocked by the DA-1 receptors antagonist SCH 23390 and by the other DA-2 receptor antagonists fluphenazine and haloperidol. DA-2 receptor responses coupled negatively to the cAMP generating system were obtained by incubating renal medulla membrane particles with DA or SKF 82526 together with SCH 23390. DA-2 receptor responses were also elicited with the receptor agonists quinpirole and bromocriptine in the absence of SCH 23390. These inhibitory effects on cAMP generation were abolished by the DA-2 receptor antagonist l-sulpiride. Our findings suggest that rat renal medulla contains DA DA-1 and DA-2 receptors similar to those found in brain and in other peripheral tissues. The physiological significance of these receptors, if any, should be established in future studies.

Animals↗