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Biomedical subjects

J B Simpson

Publications and source records attributed to J B Simpson.

At least 91 records · Page 5Linked to original sources
PubMed1979

Pharmacologic independence of subfornical organ receptors mediating drinking.

In rats with chronically implanted cannulae in the subfornical organ (SFO), the relationship between cholinergic- and angiotensin (AII)-induced drinking was investigated pharmacologically. All substances were injected via SFO cannulae which did not rupture ventricular ependyma. Pretreatment with low doses of the muscarinic antagonist atropine abolished carbachol-induced drinking, while nicotinic antagonists had no effect. Nonetheless, pretreatment with much larger doses of atropine had no effect on AII-induced drinking. Similarly, relatively small doses of the AII antagonist, saralasin, blocked AII-induced drinking, yet a much larger dose of saralasin had no effect on carbachol-induced drinking. The receptors mediating cholinergic- and AII-induced drinking therefore cannot be in series and must be in parallel. A hypothesis is proposed to account for this independence and for the significance of the SFO cholinergic innervation.

Angiotensin II↗
PubMed1978

Mechanism of the dipsogenic action of tetradecapeptide renin substrate.

The mechanism of the dipsogenic action of synthetic tetradecapeptide renin substrate (TDP) was studied in rats with chronically implanted lateral ventricular cannulae. All hormones and drugs were injected via the ventricular cannulae. The dipsogenic action of TDP was unaffected by the renin inhibitor pepstatin but was markedly reduced by the angiotensin converting enzyme inhibitor SQ 20881. Homogenates of rat brain readily formed angiotensin II from TDP in vitro and this was likewise unaffected by pepstatin but was reduced or abolished by SQ 20881 or by chelating agents. Natural renin substrate did not cause drinking and did not generate angiotensin II when incubated with brain homogenates. These results demonstrate that rat brain converting enzyme can generate angiotensin II from TDP and that this effect is responsible for the dipsogenic action of TDP.

Angiotensin II↗
PubMed1978

Localization of receptors for the dipsogenic action of angiotensin II in the subfornical organ of rat.

The proposal of the subfornical organ (SFO) as a site of receptors for drinking induced by angiotensin II (AII) was investigated with several mutually confirmatory experiments. Intracranial injections of physiological doses of AII elicited drinking if and only if applied directly to the SFO (Experiment I). Ablation of the SFO selectively (Experiment 2) and permanently (Experiment 4) eliminated drinking elicited by physiological doses of intravenously infused AII. Animals in which SFO had been ablated responded normally to cellular dehydration but reduced responding to the extracellular thirsts of beta-adrenergic activation and hyperoncotic colloid dialysis (Experiment 3). Infusion of saralasin, an AII antagonist, directly into the SFO selectively and reversibly antagonized intravenous AII drinking (Experiment 5). The hypothesis that the SFO contains dipsogenic receptors for circulating AII is strongly supported.

Angiotensin II↗
PubMed1978

Central receptor sites for angiotensin-induced drinking: a critical review.

A review of proposed sites of the dipsogenic action of angiotensin II is presented. Techniques used for such localization are critically discussed, and it is suggested that convergence of evidence from several different experimental techniques is required for localization of dipsogenic receptors. Loci suggested as such sites of action include the preoptic regions, the subfornical organ, and the tissue proximal to the optic recess of the third ventricle, including the organum vasculosum laminae terminalis. Current evidence suggests that there are at least two loci within the forebrain that possess dipsogenic receptors for angiotensin II.

Angiotensin II↗
PubMed1976

Regional differences in the morphology of the rat subfornical organ.

Based upon scanning and transmission electron microscopy 3 regions are distinguished in the rat subfornical organ. The rostral region is dominated by nerve fibers interspersed with relatively few neurons and glial cells. Squamous to low cuboidal ependymal cells with flat ventricular surfaces bearing a few short microvilli line the center of this region; laterally, ciliated cuboidal ependymal cells predominate. The central region occupies the largest area of the organ and contains most of the neuronal perikarya and glial cells. Many perikarya and neuronal processes are located immediately underneath the ependymal surface. A dense capillary network with wide pericapillary spaces permeates the tissue. In the rostral two-thirds of this region the ependymal cells are either squamous or cuboidal, sometimes with slightly bulging ventricular surfaces bearing longer microvilli. Here supraependymal neurons are particularly numerous. The caudal one-third of the central region is characterized by squamous, cuboidal and columnar ependymal cells whose hemispherical ventricular surfaces are studded with long microvilli and occasional cilia and vesicular protrusions. The caudal region, like the rostral region, is dominated by nerve fibers between which neuronal perikarya and glial cells are present. At this level the choroid plexus is attached to the SFO through highly vascularized pial connective tissue. It is the major point of penetration of the SFO's capillary plexus. The possible significance of these observations and their importance in experimental interventions are discussed.

Animals↗
PubMed1973

Subfornical organ: site of drinking elicitation by angiotensin II.

Angiotensin II applied directly to the subfornical organ in a dose as small as 0.1 nanogram elicited short-latency drinking behavior in water-sated rats. Lesions in the body of this structure blocked drinking induced by angiotensin II applied to the basal telencephalon (including preoptic area). These results call attention to the subfornical organ as an important central nervous structure involved in the conrol of drinking behavior.

Angiotensin II↗
PubMedDate not supplied

Simultaneous cannulation: a technique for percutaneous transluminal coronary angioplasty of chronic total occlusions.

Three patients with indications for percutaneous transluminal angioplasty of a totally occluded coronary artery also had distal opacification by a collateral vessel. The balloon catheter and guide wire were manipulated proximally through the guide catheter. With a second catheter, angiography of the collateral vessel opacified the occluded artery distal to the obstruction. In all three cases, simultaneous catheterization was safe and aided our assessment of distal vessel contour, length of occlusion, and the intraluminal position of the wire beyond the complete obstruction. We conclude that this technique may improve success rates for dilating chronic total obstructions by allowing safer manipulation of less flexible wires.

Angioplasty, Balloon↗
PubMedDate not supplied

Selective percutaneous "biopsy" of atheromatous plaque tissue for cell culture.

The combination of percutaneous atherectomy and angioscopy enabled a selective "biopsy" of protruding atheromatous plaque material from 11 patients with arterial occlusive disease. The removed specimens were cultivated as adhering explants or single cells were obtained by enzymatic disintegration. The vast majority of the cultivated cells resembled fibroblasts, but could be identified as smooth muscle cells by their smooth muscle alpha-actin content. Proliferation rate was slow with 0.1 doublings per day. Endothelial cells were not observed by immunologic criteria. The described biopsy technique and in vitro evaluation of cultured human atheromatous plaque material may be useful for a better understanding of atherogenesis.

Actins↗
PubMedDate not supplied

Directional coronary atherectomy for the treatment of coronary lesions with abnormal contour.

Directional coronary atherectomy is a newly developed percutaneous transluminal procedure which excises and removes obstructive tissue from coronary arteries or saphenous vein grafts. This procedure was performed on 47 lesions with abnormal contour; 24 ulcerative lesions, 10 lesions with dissection, 7 flap-like lesions and 6 lesions with aneurysm dilatation. Overall success rate was 89%; 96% in ulcerative lesions, 70% in lesions with dissection, 86% in flap-like lesions and 100% in lesions with aneurysmal dilatation. Complications with this procedure were as follows: Vessel occlusion in 2 patients (4.5%), perforation in 1 patient (2.3%), and guiding catheter induced dissection in 1 patient (2.3%). Coronary artery bypass surgery was required in 4 patients (9.4%) for these complications. Of these, 3 patients had lesions with dissections prior to the atherectomy procedure. The success rate for lesions with abnormal contour was similar to those of 270 lesions with normal contour. In conclusion, directional coronary atherectomy is a safe and effective procedure for lesions with abnormal contour, however, outcome of a lesion with dissection is suboptimal and it needs to be approached cautiously.

Angioplasty, Balloon, Coronary↗