Biomedical subjects

M De Michele

Publications and source records attributed to M De Michele.

8 recordsLinked to original sources

PubMed1992

Muscarinic cholinergic receptors in the human right coronary artery: a receptor binding and autoradiographic study.

We used a combination of radioreceptor binding and autoradiographic techniques to study the pharmacological characteristics and anatomical localization of [3H]-quinuclidinyl benzilate (QNB) binding sites in the human right coronary artery. The ligand was bound to sections of the human right coronary artery in a manner consistent with the labelling of muscarinic receptors. The addition of pirenzepine or of carbachol to the incubation medium to generate displacement curves was indicative of the presence of M1 and M2 receptors in the right coronary artery. Autoradiography showed the localization of M1 sites primarily in the medial layer of the right coronary artery. M2 sites were located primarily in the adventitia. No [3H]-QNB binding sites were observed in the endothelium. A possible role of muscarinic receptors in the pathogenesis of coronary vasospasm is discussed.

Adolescent↗

PubMed1991

Decreased density of beta-adrenergic and muscarinic cholinergic receptor sites in the vasa nervorum of aged rats.

The pharmacological profile and the anatomical localization of beta-adrenergic and muscarinic cholinergic receptors of the vasa nervorum were studied in sections of sciatic nerve using radioreceptor binding and light microscope autoradiography techniques. Sprague-Dawley rats of 4 and 24 months of age were used. [3H]Dihydroalprenolol (DHA) and [3H]quinuclidinyl benzilate (QNB) were used to label beta-adrenergic and muscarinic cholinergic receptors, respectively. The ligands were bound to sections of rat sciatic nerve in a manner consistent with the labelling of beta-adrenergic or muscarinic cholinergic receptors in the 2 age groups investigated. The dissociation constant (Kd) values (about 1.37 nM for [3H]DHA and 0.75 nM for [3H]QNB) did not significantly change between 4- and 24-month-old rats. The maximum concentration of binding sites (Bmax) for [3H]DHA was decreased by about 35% in 24 in comparison with 4-month-old rats. The Bmax value for [3H]QNB was reduced by about 50% in the aged rats. Light microscope autoradiography revealed the development of specific silver grains in the medial layer of epineurial and perineurial arteries in sections of sciatic nerve exposed either to [3H]DHA or [3H]QNB. The number of silver grains developed in epineurial and perineurial arteries of rats of 24 months is significantly lower than in animals of 4 months. The above results suggest the occurrence of an age-dependent loss in the density of beta-adrenergic and muscarinic cholinergic receptors of vasa nervorum. Vasa nervorum are the blood vessels which supply peripheral nerve trunks. They are constituted by outer (epineurial) and inner (perineurial) arteries and veins as well as by a capillary (endoneurial) plexus. Vasa nervorum are innervated by both sympathetic and non-sympathetic nerves which probably play a role in the pathogenesis of some neuropathies. Several different neurotransmitter containing nerve fibres have been identified in the vasa nervorum perivascular plexuses. However, no information is so far available concerning the neurotransmitter receptors of vasa nervorum. Moreover, although the occurrence of age-dependent changes in peripheral nerve morphology and function is well documented, very few reports were centered on the age-dependent changes of the vasa nervorum. The aims of the present study were to characterize pharmacologically and to localize anatomically the beta-adrenergic and muscarinic cholinergic receptors in the rat vasa nervorum. Moreover, the effect of ageing on the density and pattern of these receptors was investigated.

Aging↗

PubMed1991

Autoradiographic localization of muscarinic acetylcholine receptors in the rat pulmonary vascular tree.

The pharmacological characteristics and the anatomical localization of muscarinic receptors in the pulmonary vascular tree were investigated in lung sections of Wister-Kyoto (WKY) and spontaneously hypertensive rats (SHR). [3H]Quinuclidinyl benzylate [( 3H]QNB) was bound by sections of rat lung in a manner consistent with the labeling of muscarinic acetylcholine receptors, with a dissociation constant value (Kd) of 0.41 +/- 0.3 nM in WKY rats and of 0.37 +/- 0.2 nM in SHR. The density of muscarinic acetylcholine receptors was higher in sections of lung of WKY rats than of SHR. In the pulmonary vasculature these sites were associated with the smooth muscle of the medial layer of different size branches of the pulmonary artery and vein. No [3H]QNB binding sites were found within the endothelium in the blood vessels of either WKY rats or SHR. The density of [3H]QNB binding sites was significantly lower in the smooth muscle of pulmonary vein and its branches in SHR. There were no significant hypertension-dependent changes in the density and pattern of muscarinic receptors of pulmonary artery smooth muscle.

Animals↗

PubMed1991

Vasoactive intestinal polypeptide receptors in rat cerebral vessels: an autoradiographic study.

1. Localization and pharmacological properties of the vasoactive intestinal polypeptide (VIP) receptors in rat circle of Willis arteries and in the arteries of pial-arachnoid membrane were studied using light microscope autoradiography combined with radioreceptor binding techniques. 2. [125I]-VIP was specifically bound to sections of rat cerebral arteries with a dissociation constant value of 0.5 nM and a binding site density of 80 fmol mg protein-1. Radioreceptor binding experiments revealed that the binding characteristics of [125I]-VIP were consistent with the labelling of specific VIP receptors. The rank order of potency of various substances tested to inhibit [125I]-VIP binding was the following: VIP greater than peptide histidine methionine greater than secretin greater than glucagon. 3. Light microscope autoradiography revealed the localization of [125I]-VIP binding sites in the medial layer of circle of Willis and pial arteries. Quantitative determination of [125I]-VIP binding site density in the different circle of Willis arteries demonstrated a higher accumulation of silver grains in the anterior than in the posterior cerebral arteries. Pial arteries are richer in VIP receptor sites than circle of Willis arteries. 4. These results suggest that the physiological neurogenic vasodilation elicited by VIP on cerebral arteries is mediated by the interaction with specific receptor sites located primarily within cerebral vessels structures involved in the control of cerebrovascular resistances.

Animals↗

PubMed1991

Update on calcium antagonists in cerebrovascular diseases.

Clinical management of patients affected by subarachnoid hemorrhage has been modified by the use of nimodipine. Although no differences in overall neurologic outcome and rates of symptomatic spasm have been observed between nimodipine and control patients, severity of permanent neurologic deficits consequent to cerebral vasospasm is reduced in the former. On the other hand, clinical trials with nimodipine in ischemic stroke did not substantiate the expected neurologic benefits. A meta-analysis of the two phase IV studies published thus far shows that of 350 patients examined, mortality rate was 11.5% and 19% in subjects given nimodipine and placebo, respectively (n.s.). Cerebral death accounted for 30% of cases in both groups, whereas a lower percentage of cardiac and pulmonary fatal events were observed among nimodipine-treated subjects. Moreover, neurologic outcome of survivors was not significantly different. These results may be associated with the notion that the voltage-operated channel blockade exerted by calcium antagonists is only a part of the complex events leading to the enhancement of calcium ion intracellular concentration as a "common final pathway." However, difficulties encountered in planning clinical trials in acute ischemic stroke also might explain the lack of conclusive results. The feasibility of randomization of an adequate sample of patients and of very early therapeutic intervention after stroke onset are discussed.

Brain Ischemia↗

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↗

PubMed1989

Autoradiographic localization of muscarinic receptors within the rat kidney.

We used a combination of radioreceptor binding and autoradiographic techniques to study the pharmacological characteristics and anatomical localization of [3H]quinuclidinyl benzylate (QNB) in kidney sections of Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). [3H]QNB was bound by sections of rat kidney in a manner consistent with the labeling of muscarinic acetylcholine receptors. Anatomically, these receptor sites were located primarily within the smooth muscle of the renal vascular tree and to a lesser extent within cortical and medullary tubules. The density of renal muscarinic acetylcholine receptors (both vascular and tubular) was decreased in hypertension but the affinity of the ligand for muscarinic receptors was unchanged. A possible role of muscarinic acetylcholine receptors in renal function is suggested.

Animals↗

PubMed1988

Increase in perivascular noradrenergic nerve density and decrease in acetylcholinesterase-positive sympathetic nerve density in the kidneys of spontaneously hypertensive rats.

The density and pattern of sympathetic nerve fibres in the kidneys of 16-week-old spontaneously hypertensive rats (SHR) and of control age-matched normotensive Wistar-Kyoto (WKY) rats were studied by catecholamine histofluorescence and acetylcholinesterase histochemical techniques. Varicose noradrenergic fibres primarily supply renal vasculature and were concentrated in small arteries and in afferent glomerular arterioles. The number and the density of these nerve fibres were increased in SHR. Acetylcholinesterase-positive nerve fibres were distributed to the renal vascular tree in the same way as the noradrenergic nerves and disappeared after chemical sympathectomy, suggesting their sympathetic nature. Acetylcholinesterase-positive perivascular nerve fibres were decreased in SHR. The possible significance of the two directional behaviour of sympathetic nerves (noradrenergic and acetylcholinesterase-positive) in the kidneys of SHR is discussed.

Acetylcholinesterase↗