P-31 nuclear magnetic resonance spectroscopic study of obstructive uropathy in the rat.

P-31 nuclear magnetic resonance (NMR) spectroscopy of the rat kidney with ureteral ligation resulted in a rapid and major increase in a peak resonating at 7096.63 +/- 0.65 Hz from the reference frequency of phosphorus (32.60 MHz). This corresponded to an increase in the concentration of the substance responsible for peak X from 0.34 +/- 0.04 mumol/g wet weight in normal kidneys to 1.45 +/- 0.27 mumol/g wet weight in unilaterally obstructed kidneys and 2.00 +/- 0.34 mumol/g wet weight in bilaterally obstructed kidneys at 3 h (P less than 0.01). Further NMR studies performed with in vivo kidneys and tissue extracts revealed that inorganic phosphate in the urine, resonating at a lower frequency due to the acid pH environment, was responsible for the increase in this peak. These findings may prove to be of fundamental interest as well as potential clinical significance.     

Effect of temporal distribution of calories on diurnal patterns of glucose levels and insulin secretion in NIDDM

The effect of different temporal patterns of calorie intake on plasma glucose, serum insulin, and insulin secretion rates was examined in six patients with moderately well controlled non-insulin-dependent diabetes mellitus (NIDDM). Patients were studied on three separate occasions over 26 h. Total calories and food composition (50% carbohydrate, 15% protein, and 35% fat) were kept constant, but the pattern of calorie intake was varied. In study A (similar meal size), calories were distributed as 30, 40, and 30% at breakfast, lunch, and dinner, respectively. In study B (3 snacks, 3 meals), each subject ate three meals of 20, 20, and 30% of calories for breakfast, lunch, and dinner, respectively, and three snacks, each comprising 10% of calories, presented 2.5 h after the meal. In study C (large dinner), 10% of calories were consumed at breakfast, 20% at lunch, and 70% at dinner. Glucose, insulin, and C-peptide concentrations were measured at 15- to 30-min intervals. Insulin secretion rates were calculated from C-peptide levels with individually derived C-peptide clearance parameters. The different eating patterns were associated with only modest differences in overall levels of glucose and insulin secretion. Daytime insulin secretion was lowest when most of the daily calorie intake occurred in the form of a large dinner. Overnight levels of glucose and insulin secretion rates did not differ for the three eating patterns, and the morning glucose levels were also unaffected by the pattern of calorie intake on the previous day. A morning rise of glucose of greater than 0.28 mM occurred consistently only when dinner was of moderate size (30% of total calories).(ABSTRACT TRUNCATED AT 250 WORDS)     

Unreliability of oxygen tension-based indices in reflecting intrapulmonary shunting in critically ill patients

Measurement of intrapulmonary shunting (Qsp/Qt), a widely used method for monitoring disturbances of pulmonary oxygen transfer in critically ill patients, involves calculation of arterial and mixed venous oxygen contents. In circumstances where mixed venous blood samples are not readily available, oxygen tension-based indices such as the alveolar to arterial oxygen tension differences (P[A-a]O2), arterial oxygen tension to alveolar oxygen tension ratio (PaO2/PAO2), PaO2 to FIO2 ratio (PaO2/FIO2) and respiratory index (RI) are widely utilized to reflect Qsp/Qt. Oxygen content-based indices such as the estimated shunt are not as widely utilized as the oxygen tension indices. In 75 critically ill patients in whom a pulmonary artery catheter was being utilized to augment clinical care, comparisons were made between Qsp/Qt and P(A-a)O2, PaO2/PAO2, PaO2/FIO2, RI, and estimated shunt to determine which index best reflected Qsp/Qt. Correlations between Qsp/Qt and estimated shunt were good (r = .94) and poor for the P(A-a)O2 (r = .62), PaO2/PAO2 (r = .72), PaO2/FIO2 (r = .71), and RI (r = .74). We conclude that there are no real substitutes for venous oxygen contents in critically ill patients. When pulmonary artery blood is not available for analysis, oxygen tension-based indices are unreliable reflectors of Qsp/Qt while the estimated shunt, an oxygen content-based index, provides a more reliable reflection of Qsp/Qt.     

On the adaptation in potassium excretion associated with nephron reduction in the dog

An effort to examine certain aspects of the adaptation in potassium excretion associated with nephron reduction was made in dogs with unilateral remnant kidneys. A constant intake of potassium was maintained by tube feeding and studies were performed before and after removal of the intact control kidney. The removal of the intact kidney created the need for the remaining nephrons of the remnant kidney to increase their rate of potassium excretion markedly. Sodium intake was held constant either at a normal or a low level. Mineralocorticoid hormone activity was maintained either at a high level by the administration of 0.2 mg 9-α-fluorohydrocortisone daily or at a low level by performing bilateral adrenalectomy and administering a minimal maintenance dose of deoxycorticosterone acetate (DOCA) and cortisol. Potassium excretion per nephron increased strikingly within 18 hr of contralateral nephrectomy and by 7 days, excretion rates were 600% of control values for the remnant kidney. More potassium was excreted in the first 5 hr after administration of a test dose of potassium by the remnant kidney alone in the postnephrectomy state than by both the remnant and intact kidneys in the prenephrectomy state. 24 hr excretion of potassium by the remnant kidney postnephrectomy averaged 92% of the administered load of potassium. The adaptation in potassium excretion was independent of the concurrent rate of sodium excretion and of mineralocorticoid hormone activity and persisted during constriction of the renal artery, a stimulus which presumably decreased distal delivery of sodium. The adaptation and the continued modulation of potassium excretion could not be explained adequately by an increase in impermeant anion excretion per nephron. Finally, known changes in hydrogen ion excretion per nephron associated with nephron reduction are in a direction opposite to those which would explain the acquired kaliuresis per nephron.     

Role of L-thyroxine in nuclear thyroid hormone receptor occupancy and growth hormone production in cultured GC cells.

The contribution of L-thyroxine (T4) to nuclear thyroid receptor occupancy was studied in GC cells incubated with concentrations of 3,5,3'-triiodo-L-thyronine (T3) and T4 that resulted in free iodothyronine levels similar to those in serum of euthyroid rats. T4 accounted for 5.4-10% of the occupied receptors: T3 derived from T4 [T3(T4)] and T3 added to medium accounted for the remainder of receptor occupancy. Incubation with increasing medium free T4 resulted in a progressive increase in the contribution of T4 and T3(T4) to receptor occupancy. In incubations with 3.6-fold increased medium free T4, T4 accounted for 20.4%, and T3(T4) for 40.3% of receptor occupancy. These occupancy data and the experimentally determined Ka of thyroid receptor for T3 and T4 allowed calculation of nuclear free iodothyronine concentrations. Nuclear free T3 was 3-6-fold greater than medium free T3 and nuclear [corrected] free T4 was 12-19-fold greater than medium free T4. When GC cells were incubated with decreased medium free T3 and physiological medium free T4, both nuclear receptor occupancy and growth hormone production decreased as well. However, a twofold increase in medium free T4, in the presence of decreased medium free T3, restored receptor occupancy and growth hormone production to or near control values. These findings establish a role for T4 in addition to T3(T4) in nuclear receptor occupancy and biological activity in rat anterior pituitary tissue both in physiologic conditions and when medium free T4 is raised. The findings may have relevance to the sick euthyroid thyroid syndrome in which free T4 may be increased in some patients who have decreased serum free T3.     

Decreased expression of human class II antigens on monocytes from patients with acquired immune deficiency syndrome. Increased expression with interferon-gamma

The expression of HLA-DR (a class II histocompatibility antigen) on monocytes isolated from the peripheral blood of normal individuals and patients with acquired immune deficiency syndrome (AIDS) was investigated by the use of dual fluorescent staining and cytofluorometry. In animal models the absence of class II positive monocytes is linked to a failure of T cells to respond to antigens. We now report that patients with AIDS have a paucity of HLA-DR+ monocytes. The percentage of HLA-DR+ monocytes among eight normal individuals ranged from 49.3 to 95.0%+, and only one individual had less than 50% HLA-DR+ monocytes. HLA-DR expression on monocytes from homosexual male patients with lymphadenopathy was similar to that of normal subjects (range, 58.0 to 97.4%+). In contrast, seven of nine patients with AIDS had less than 50% HLA-DR+ monocytes (range, 13.4 to 78.8%+). The in vitro incubation of monocytes from AIDS patients with cloned human interferon-gamma resulted in an increase of the expression of HLA-DR to near normal levels.     

Protease-activated receptors 1 and 4 mediate activation of human platelets by thrombin

Because of the role of thrombin and platelets in myocardial infarction and other pathological processes, identifying and blocking the receptors by which thrombin activates platelets has been an important goal. Three protease-activated receptors (PARs) for thrombin -- PAR1, PAR3, and PAR4 -- are now known. PAR1 functions in human platelets, and the recent observation that a PAR4-activating peptide activates human platelets suggests that PAR4 also acts in these cells. Whether PAR1 and PAR4 account for activation of human platelets by thrombin, or whether PAR3 or still other receptors contribute, is unknown. We have examined the roles of PAR1, PAR3, and PAR4 in platelets. PAR1 and PAR4 mRNA and protein were detected in human platelets. Activation of either receptor was sufficient to trigger platelet secretion and aggregation. Inhibition of PAR1 alone by antagonist, blocking antibody, or desensitization blocked platelet activation by 1 nM thrombin but only modestly attenuated platelet activation by 30 nM thrombin. Inhibition of PAR4 alone using a blocking antibody had little effect at either thrombin concentration. Strikingly, simultaneous inhibition of both PAR1 and PAR4 virtually ablated platelet secretion and aggregation, even at 30 nM thrombin. These observations suggest that PAR1 and PAR4 account for most, if not all, thrombin signaling in platelets and that antagonists that block these receptors might be useful antithrombotic agents.     

Histopathological validation of high frequency epicardial echocardiography of the coronary arteries in vitro

The accuracy and reliability of measurement of coronary artery dimensions and detection of atherosclerotic lesions by high frequency epicardial echocardiography were compared with histopathological results. Ten pressure perfused human hearts were examined in vitro with a 10 MHz (Diasonics) transducer and a 7.5 MHz (Vingmed/Sonotron) transducer. There was close agreement between ultrasound and pathological measurements of coronary artery luminal diameter. Qualitative changes in wall structure such as diffuse wall thickening and calcification were readily identified; however, the resolution of the transducers was not high enough accurately to measure wall dimensions in normal coronary arteries. Coefficient of variation measurements for intra and inter observer variability (5.2% and 6.9% respectively) showed excellent reproducibility. The technique was accurate in identifying atherosclerotic lesions, imaging arteries distal to an occlusion, locating deeply sited arteries, and identifying complete obliteration of an artery. Intraoperative video playback and transducer miniaturisation may minimise problems caused by cardiac movement and restricted access. With these developments intraoperative assessment of coronary artery disease may become a real possibility.     

MRI detection of single particles for cellular imaging

There is rapid growth in the use of MRI for molecular and cellular imaging. Much of this work relies on the high relaxivity of nanometer-sized, ultrasmall dextran-coated iron oxide particles. Typically, millions of dextran-coated ultrasmall iron oxide particles must be loaded into cells for efficient detection. Here we show that single, micrometer-sized iron oxide particles (MPIOs) can be detected by MRI in vitro in agarose samples, in cultured cells, and in mouse embryos. Experiments studying effects of MRI resolution and particle size from 0.76 to 1.63 microm indicated that T(2)* effects can be readily detected from single MPIOs at 50-microm resolution and significant signal effects could be detected at resolutions as low as 200 microm. Cultured cells were labeled with fluorescent MPIOs such that single particles were present in individual cells. These single particles in single cells could be detected both by MRI and fluorescence microscopy. Finally, single particles injected into single-cell-stage mouse embryos could be detected at embryonic day 11.5, demonstrating that even after many cell divisions, daughter cells still carry individual particles. These results demonstrate that MRI can detect single particles and indicate that single-particle detection will be useful for cellular imaging.