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Biomedical subjects

J Mason

Publications and source records attributed to J Mason.

At least 235 records · Page 13Linked to original sources
PubMed1985

Drug effects on memory: assessment of a combined active and passive avoidance task.

We evaluate a little-known avoidance task first described by Carew, which enables the simultaneous assessment of two indices relevant to the study of memory processes, passive avoidance re-entry latency, and active avoidance choice. As an illustration, the effects of 0, 1 and 10 mg/kg amphetamine, peripherally injected immediately following the learning trial, were studied using two different shock intensity conditions (mild and moderate). The latency measure indicated that the drug improved consolidation, but the choice measure suggested that this enhancement was at best marginal; shock intensity was found to be a critical factor. It is concluded that this unique task is superior to some traditional avoidance techniques used in assessing memory.

Amphetamine↗
PubMed1985

Acute bereavement, threatened loss, ego defenses and adrenocortical function.

In this study of 43 acutely bereaved widows and widowers and a comparison group of 24 nonbereaved married persons who experienced critical illness in a spouse, we found no evidence of higher levels of affective arousal, higher levels of adrenocortical activity, less effective ego defenses, or higher levels of defensive work among bereaved persons by comparison with nonbereaved persons. Furthermore, we failed to observe expected relationships between ego defensive function and adrenocortical activity among either bereaved or nonbereaved persons. These observations are consistent with one previous study of bereaved parents.

Arousal↗
PubMed1985

Electrophysiologic testing in patients with the long QT syndrome.

Electrophysiologic studies were performed in 15 patients with syncope and/or cardiac arrest who had the long QT syndrome and 11 control subjects who had normal QT intervals. The syndrome was familial in five patients and idiopathic in 10. All patients had a prolonged QT (546 +/- 68 msec, mean +/- SD) and corrected QT (550 +/- 51 msec). Incremental atrial pacing at cycle lengths of 600 to 400 msec resulted in shortening of the QT interval, but there was no significant difference in the magnitude or percent of shortening of the QT interval between patients with the long QT syndrome and control subjects. Intravenous propranolol did not influence the QT interval measured at fixed atrial-paced cycle lengths in patients with either the familial or idiopathic form of the syndrome. Programmed right and left ventricular stimulation with up to three extrastimuli before and during isoproterenol infusion did not induce sustained ventricular tachycardia or ventricular fibrillation in any of the patients. However, rapid polymorphic nonsustained ventricular tachycardia was induced in six of the 15 patients (40%). Neither the inducibility of nonsustained ventricular tachycardia nor the results of electropharmacologic testing with beta-blockers proved to be of any prognostic value during the mean follow-up period of 28 +/- 17 months. Electrophysiologic studies are of limited value in the diagnosis and treatment of patients with the long QT syndrome.

Adolescent↗
PubMed1985

The norepinephrine-to-epinephrine ratio in patients with a history of suicide attempts.

Norepinephrine and epinephrine were measured serially in 24-hour urine collections from 99 male psychiatric inpatients with mixed diagnoses. The group was blindly divided into those with a previous history of at least one suicide attempt (N = 38) and those without such a history (N = 61). The ratio of norepinephrine-to-epinephrine levels was significantly lower in the group with a history of suicide attempts. The authors discuss the possibility that a low norepinephrine-to-epinephrine ratio is a risk factor for suicidal behavior.

Adult↗
PubMed1984

Role of the medullary perfusion defect in the pathogenesis of ischemic renal failure.

Experiments were performed on rats to investigate the significance of the medullary hyperemia known to follow renal ischemia. To this end, its frequency was determined, its severity was quantified, and its relation to renal function was examined early (1 to 3 hr) and later (18 hr) after 45 min of warm ischemia. All kidneys were found to have a hyperemic outer medulla early after ischemia, which was shown to develop during the period of ischemia itself, but which was found to be highly variable in its severity. The degree of hyperemia was assessed both subjectively by grading and by histometric determinations of inner stripe capillary volume. One to hours after ischemia, the severity of medullary hyperemia was reflected in all indices of renal function, the least congested kidneys showing the best function. Eighteen hours after ischemia, the degree of medullary hyperemia was reflected in all indices of renal function, except urine flow rate; the non-congested kidneys showed functional recovery and the still-congested kidneys showed worsening function. Glomerular blood flow, known to be preferentially reduced in deep nephrons 1 to 3 hr after ischemia, had normalized 18 hr after ischemia in the non-congested kidneys but was still severely and unevenly depressed in the congested kidneys. It is concluded that congestion of the outer medulla is a key event in ischemic renal failure, its occurrence is coincidental with the reduction in deep nephron perfusion and urinary concentrating power in the early and maintenance phase and its disappearance heralds the restoration of deep nephron perfusion and urinary concentrating ability in the recovery phase.

Acute Kidney Injury↗
PubMed1984

Some studies on the metabolism and the effects of 99Mo- and 35S-labelled thiomolybdates after intravenous infusion in sheep.

Sheep were infused intravenously with 99Mo- and 35S-labelled tri- and tetrathiomolybdates (1-2 mg Mo). Most of the plasma radioactivity was trichloroacetic acid (TCA)-insoluble after infusion, but the stability of this fraction was reduced by pre-infusion or subsequent infusion with unlabelled thiomolybdates. Most of the 99Mo and 35S was shown to be associated with albumin. It was concluded that compounds bound to albumin were relatively stable, but displaced or unbound thiomolybdates were rapidly hydrolysed to molybdate and sulphate. There was no evidence of an irreversible interaction of either 35S or 99Mo with copper in plasma, despite the appearance of a TCA-insoluble Cu fraction. Increased dietary Cu did not increase the retention of 35S in plasma or affect the exchangeability of 36S-labelled thiomolybdates bound to albumin.

Animals↗
PubMed1984

A comparison of dobutamine infusion and supine bicycle exercise for radionuclide cardiac stress testing.

We have compared the inotropic drug dobutamine to supine bicycle exercise as a means of inducing stress in radionuclide ventriculography studies. Dobutamine has the following properties, making it favorable for widespread usage: 1) ability to be given safely in a peripheral vein, 2) rapid onset, and 3) short duration of action. Each patient underwent supine bicycle progressive resistance testing of 2 minutes per stage followed 30 minutes later by dobutamine administration. Accuracy of diagnosis was 0.93 and sensitivity was 0.89 with dobutamine, while with bicycle the accuracy was 0.93 and sensitivity was 0.94. While not designed to replace supine bicycle testing, incremental infusions of dobutamine appear to be nearly equal in accuracy and sensitivity, providing a satisfactory technique for cardiac evaluation of previously excluded patients.

Catecholamines↗
PubMed1984

Efficacy of left cardiac sympathectomy in the treatment of patients with the long QT syndrome.

Ten patients with the long QT syndrome and recurrent syncope and/or cardiac arrest caused by ventricular arrhythmias underwent left stellate (one patient) or left cervicothoracic sympathectomy (nine patients) after failing to respond to high-dose beta-blocker therapy. The syndrome was familial in four and idiopathic in six. All patients had a prolonged resting QT interval (548 +/- 51 msec, mean +/- SD) and corrected QT interval (QTc) (556 +/- 43 msec). After sympathectomy the mean QTc shortened significantly from 556 +/- 43 to 508 +/- 65 msec (p less than .05) but the QTc remained abnormal in all but one patient. Over a mean follow-up period of 38.6 +/- 19 months, eight patients developed recurrent symptoms that included cardiac arrest in three (one fatal, two nonfatal), syncope in four, and presyncope in six. The addition of beta-blockers was ineffective in suppressing the recurrent symptoms. The control of symptoms required more extensive sympathectomy (three patients), chronic atrial pacing (three patients), and implantation of an automatic internal defibrillator (one patient). Only one patient has remained asymptomatic without drug or pacemaker therapy. In conclusion, left cervicothoracic sympathectomy proved inadequate for long-term control of symptoms in most patients with the long QT syndrome. These patients usually required concomitant drugs, more extensive surgery, or long-term cardiac pacing for symptomatic relief.

Adolescent↗
PubMed1983

The absorption of labelled molybdenum compounds in sheep fitted with re-entrant cannulae in the ascending duodenum.

The absorption of labelled molybdenum compounds was studied in pairs of sheep exchanging digesta via re-entrant duodenal cannulae. Tri- and tetrathiomolybdate 99Mo were rapidly absorbed from the rumen to circulate in plasma in a protein-bound and in a TCA-insoluble form. The compounds were also absorbed from the small intestine although some breakdown was evident. Initially, molybdate was poorly absorbed from the rumen but after several hours the concentration of protein-bound, TCA-insoluble 99Mo increased in plasma. This provides evidence of rumen thiomolybdate synthesis. The results indicate that thiomolybdates are absorbed directly from the rumen and despite the sensitivity of the compounds to acid, some absorption from the small intestine occurs after passage through the abomasum. Rumen absorption could be a contributory factor to ruminant sensitivity to the effects of Mo compounds.

Absorption↗
PubMed1983

99Mo metabolism in sheep after the intravenous injection of [99Mo] thiomolybdates.

[99Mo]di-, tri-, and tetrathiomolybdate (5.4 to 62.5 mg of Mo) were given by intravenous injection to sheep maintained on a sulfur-supplemented (3 g of S/kg) diet. All the compounds were metabolized very rapidly over the first 15 min postinjection, but relatively slowly thereafter, with a t1/2 of about 30 hr for dithiomolybdate and 40 h for tri- and tetrathiomolybdate. The [99Mo] metabolites present in plasma were identified by Sephadex G-25 chromatography. The main fate of the compounds injected appeared to be stepwise transformation to molybdate and subsequent rapid urinary elimination. Over 90-100 hr more than 90% of the radioactivity was excreted in urine, compared to less than 5% in the feces. The trichloroacetic acid (TCA) solubility of plasma copper and the diamine oxidase activity of ceruloplasmin was depressed, particularly over the first 15 min postinjection and a more persistant TCA-insoluble Cu fraction was apparent.

Animals↗
PubMed1983

Disparity between surface and deep nephron function early after renal ischemia.

Experiments were performed using a variety of methods to assess the functional status of different nephron populations following 45 min of renal ischemia in the rat. Micropuncture techniques revealed that SNGFR and reabsorption in the surface nephrons are only modestly reduced after ischemia, whereas kidney GFR and reabsorption are more severely affected. Determinations of bolus velocity with the Hanssen technique or of glomerular blood flow with the microsphere method confirmed that both were highest in the surface nephrons, lower in the middle nephrons and lowest of all in the juxtamedullary nephrons after ischemia. It is concluded that surface nephron function is well-maintained following ischemia and that it is the functional deficiency of the deeper nephrons that is predominantly responsible for the impairment in whole kidney function. Although the pathogenic mechanism is not yet clear, neither tubular obstruction nor tubular leakage in the deeper nephrons seems to be involved. The present findings suggest that micropuncture of the surface nephrons is a technique of questionable validity for studying this type of acute renal failure, they explain the inability of the kidney to concentrate the final urine, and they predict a more pronounced deficiency in medullary than in outer cortical blood flow.

Acute Kidney Injury↗
PubMed1983

Perturbation analysis of tubuloglomerular feedback in hydropenic and hemorrhaged rats.

A closed-feedback-loop method was used to investigate regulation of SNGFR and distal fluid delivery by tubuloglomerular feedback (TGF) in hydropenic and hemorrhaged rats. Unblocked nephrons were perturbed by early proximal perfusion of previously collected, inulin-free, tubular fluid at 0, 7.5, and 15 nl/min, thereby increasing nephron fluid load. The resultant changes in SNGFR, tubular reabsorption, proximal intratubular pressure, and early distal flow were measured. During perfusion, SNGFR decreased and distal flow increased; the effect on reabsorption was variable. Analysis of the data indicated that the combined action of TGF and changes in proximal tubule and Henle's loop reabsorption were able to provide a maximum of 56% compensation for the effect of the perturbation on distal delivery in hydropenic rats and 70% compensation in hemorrhaged rats. In one group of hydropenic rats in which a significant fall in reabsorption was found, the total fluid load presented to the nephron, SNGFR plus the perfusion rate, was significantly better regulated than distal delivery. This result is consistent with the behavior of a model used to estimate the contribution of TGF to the observed regulation. The results indicated that TGF alone could provide 56% compensation for the perturbation in hydropenia and a significantly greater 72% compensation following hemorrhage. The conclusions are 1) that the properties of TGF are sufficient to result in significant regulation of distal fluid delivery and SNGFR, 2) that hemorrhage increases the strength of the TGF response, and 3) that TGF regulation of SNGFR and distal delivery is strongly influenced by changes in proximal tubule and loop of Henle reabsorption.

Animals↗
PubMed1982

Factors affecting duodenal ulcer healing. Four double-blind trials in 193 patients.

An analysis of four double-blind endoscopically controlled trials carried out in 1978 -1980 is presented. Drugs utilized were (patient numbers in brackets): a new histamine H2-receptor antagonist ranitidine (25) v. placebo (22), the colloidal bismuth ulcer-coating preparation bicitropeptide (24) v. cimetidine (26), the tricyclic antidepressant trimipramine (20) v. placebo (19), and the disaccharide coating preparation sucralfate (29) v. placebo (28). Factors analysed were smoking, alcohol consumption, age, length of history, sex and race. The prevalence of smoking and alcohol use, age and length of history varied in the four trials. Pronouncements regarding these factors based on small trials are therefore unreliable. There were no overall diffeences in healing rates whether the patient smoked, consumed alcohol, was above or below 40 years of age, or had a history shorter or longer than 1 year. Comparison of drug and placebo responses revealed that the differences between these were most significant in: non-smokers (P=0,0010) compared with smokers (P=0,0288); teetotallers (P<0,005) compared with alcohol consumers (NS); history under 1 year (P<0,005) compared with over 1 year (P<0,025); males (<0,01) compared with females (NS); and Indians (P<0,005) compared with Blacks (NS).

Adult↗
PubMed1982

Element concentrations of renal and hepatic cells under potassium depletion.

The effect of dietary potassium depletion on nuclear and cytoplasmic element concentrations in cortical renal tubular cells and hepatocytes was investigated using electron microprobe analysis. Significant differences in sodium and potassium concentrations between nucleus and cytoplasm were not detected either under control or under potassium-depleted conditions. Potassium depletion for at least 14 days resulted in a decrease in plasma potassium concentration from 4.4 +/- 0.1 to 2.0 +/- 0.1 mmoles X liter-1. There was a fall in cellular potassium from 151.6 +/- 3.5 to 120.2 +/- 2.1 in distal tubular cells, from 150.1 +/- 2.6 to 117.7 +/- 1.2 in proximal tubular cells, and from 140.6 +/- 1.3 to 128.0 +/- 1.3 mmoles X kg-1 of wet wt in hepatocytes. The cellular chlorine concentrations fell from 19.9 +/- 0.7 to 15.8 +/- 0.3 and from 21.3 +/- 0.4 to 17.2 +/- 0.4 in proximal tubular and liver cells, respectively, but remained unchanged at 11.4 +/- 0.7 and 11.0 +/- 0.4 mmoles X kg-1 of wet wt in distal tubular cells. The intracellular sodium concentrations rose from 10.4 +/- 0.7 to 15.8 +/- 0.8, 19.1 +/- 0.8 to 24.1 +/- 0.7 and 14.1 +/- 0.5 to 16.2 +/- 0.6 mmoles X kg-1 of wet wt in distal tubular, proximal tubular and liver cells, respectively. This rise in cellular sodium was insufficient in any cell type to compensate for the loss of potassium. No significant differences were found in the cellular electrolyte concentrations of the various distal tubular cell types which are thought to be involved in either potassium reabsorption or secretion. The decrease in potassium concentrations in distal tubular cells by about 20% does not seem sufficient to explain the marked fall in urinary potassium excretion.

Animals↗