Metabolism and disposition of [14C]dibromoacetonitrile in rats and mice following oral and intravenous administration.

1. Tissue distribution, metabolism, and disposition of oral (0.2-20 mg/kg) and intravenous (0.2 mg/kg) doses of [2-(14)C]dibromoacetonitrile (DBAN) were investigated in male rats and mice. 2. [(14)C]DBAN reacts rapidly with rat blood in vitro and binds covalently. Prior depletion of glutathione (GSH) markedly diminished loss of DBAN. Chemical reaction with GSH readily yielded glutathionylacetonitrile. 3. About 90% of the radioactivity from orally administered doses of [(14)C]DBAN was absorbed. After intravenous administration, 10% and 20% of the radioactivity was recovered in mouse and rat tissues, respectively, at 72 h. After oral dosing, three to four times less radioactivity was recovered, but radioactivity in stomach was mostly covalently bound. 4. Excretion of radioactivity into urine exceeded that in feces; 9-15% was exhaled as labeled carbon dioxide and 1-3% as volatiles in 72 h. 5. The major urinary metabolites were identified by liquid chromatography-mass spectrometry, and included acetonitrile mercaptoacetate (mouse), acetonitrile mercapturate, and cysteinylacetonitrile. 6.The primary mode of DBAN metabolism is via reaction with GSH, and covalent binding may be due to reaction with tissue sulphydryls.

Selective inhibition of cytochrome P450 2E1 in vivo and in vitro with trans-1,2-dichloroethylene.

The effect of trans-1,2-dichloroethylene (DCE), an inhibitor of cytochrome P450 (P450) 2E1, on the catalytic activities and total content of hepatic P450 was determined in vivo and in vitro. Hepatic microsomes were prepared from groups of rats prior to dosing and at 2, 5, 12, and 24 h postdosing, and total P450 content and the activities of P450 1A2, P450 2A1, P450 2B, P450 2C6, P450 2C11, P450 2D1, P450 2E1, and P450 3A were determined. The lowest dose of DCE that yielded maximal inactivation of P450 2E1 was found to be 100 mg/kg. Significant decreases in total content of P450 or the activities of P450 1A2, P450 2A1, P450 2B, P450 2C6, P450 2C11, P450 2D1, and P450 3A were not observed during the 24 h following administration of DCE (100 mg/kg ip), but P450 2E1 activity was diminished about 65% at 2 and 5 h after DCE treatment and returned to control levels at 24 h. Additionally, there was little or no significant effect on the activities of hepatic cytosolic alcohol dehydrogenase or mitochondrial or microsomal aldehyde dehydrogenases 5 h postdosing. DCE showed the same selectivity for P450 inactivation in vitro, and P450 2E1 activity was inhibited by >80% without affecting the other isozymes. However, DCE (5 mM) also proved to be a good competitive inhibitor of the probe activities of P450 1A2 and P450 2C6. The in vivo inhibition of P450 2E1 was accompanied by decreases in the levels of the immunoreactive protein, and an additional immunoreactive band appeared at ca. 30 kDa in the Western blot of microsomes from DCE-treated rats, possibly arising from proteolytic degradation of P450 2E1 protein after covalent modification by the inhibitor. DCE is an effective, relatively nontoxic inhibitor of P450 2E1 in vivo and in vitro that has greater selectivity than other agents currently used.

Racial differences in the age-related increase in left ventricular mass in youths.

We determined the factors related to left ventricular mass adjusted for body size in 60 black (mean age, 13 +/- 2 years) and 40 white (mean age, 14 +/- 2 years) normotensive youths. The factors examined included age, sex, systolic blood pressure, diastolic blood pressure, plasma renin activity, plasma aldosterone concentration, and sodium and potassium intake as determined by 24-hour excretion. Sex (beta = 13.3, P < .003), age (beta = 2.88, P < .001), and systolic blood pressure (beta = 0.41, P < .02) were independent predictors in the sample as a whole, accounting for 37% of the variance of left ventricular mass adjusted for height. Separate analyses were performed for black and white subjects. In the black subjects, age (beta = 4.4, P < .004) followed by sex (beta = 11.85, P < .02) were independent factors, accounting for 43% of the variance of left ventricular mass adjusted for height. In contrast, in white subjects systolic blood pressure (beta = 0.4, P < .003) followed by sodium excretion (beta = 0.13, P < .05) were independent factors, with gender (beta = 8.89, P < .07) tending to account for 36% of the variance. Similar results were observed for left ventricular mass adjusted for body surface area. In conclusion, the age-related increase in adjusted left ventricular mass in black but not white youths may in part account for the early development of cardiovascular disease among the black population.

Cardiac function in fetuses and newborns exposed to low-dose aspirin during pregnancy.

OBJECTIVE: Our purpose was to evaluate cardiac function in fetuses exposed to low-dose aspirin. STUDY DESIGN: To assess its efficacy in preventing preeclampsia, 60 mg/day aspirin or a matching placebo was administered to women in a double-blind fashion during the second and third trimesters. As a part of this study, 146 echo Doppler studies were performed on 63 fetuses from 15 to 40 weeks' gestation. These studies allowed assessment of systolic and diastolic cardiac function. Cardiac function was also assessed in 87 neonates. RESULTS: Throughout gestation ductus arteriosus flow velocity, right ventricular output and diastolic area, and left ventricular output and diastolic area all increased and were similar in both aspirin- and placebo-exposed fetuses. Fetal diastolic flow velocities were also alike in both groups. The two groups had similar gestational ages at delivery (39.2 +/- 2.3 vs 38.7 +/- 2.7 weeks) and birth weights (3174 +/- 575 vs 3105 +/- 579 gm, respectively). Furthermore, there was no difference in fractional shortening, cardiac output, prevalence of tricuspid regurgitation, or patency of the ductus arteriosus at birth between the two groups. CONCLUSION: The circulation of fetuses and newborns is not affected adversely by exposure to low-dose aspirin during gestation.

Ambulatory blood pressure recordings in children and adolescents.

OBJECTIVE: To provide reference data for ambulatory blood pressure monitoring (ABPM) and to determine the influence of age, sex, and race on these values. METHODS: ABPM was performed on 300 healthy, normotensive boys and girls between the ages of 10 and 18 years, including 160 boys and 140 girls, of whom 149 were white and 151 were black. Mean systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) while awake and during sleep were calculated for black and white boys and girls aged 10 to 12 years, 13 to 15 years, and 16 to 18 years. RESULTS: Boys compared with girls 10 to 12 years of age had higher mean (+/- SD) SBP (115 +/- 9 vs 112 +/- 9 mm Hg; P < .01) and DBP (67 +/- 7 vs 65 +/- 5 mm Hg; P < .01) while awake. Boys compared to girls 13 to 15 years of age had higher SBP while awake (116 +/- 11 vs 112 +/- 8 mm Hg; P < .01). Boys compared with girls 16 to 18 years of age had higher SBP while awake (125 +/- 12 vs 111 +/- 9 mm Hg); P < .01) and during sleep (116 +/- 11 vs 106 +/- 9 mm Hg). Comparisons within sex showed similar changes with age for boys and girls. Blacks compared with whites 13 to 15 years of age had higher SBP during sleep (109 +/- 11 vs 105 +/- 10 mm Hg; P < .01), and blacks compared with whites 16 to 18 years of age had higher DBP during sleep (66 +/- 7 vs 58 +/- 6 mm Hg; P < .01). Comparisons across age groups within race showed that blacks 16 to 18 years of age had higher SBP during sleep than blacks 10 to 12 years of age (109 +/- 11 vs 104 +/- 10 mm Hg), and higher DBP during sleep (66 +/- 7 mm Hg; P < .01) than blacks 10 to 12 years of age (61 +/- 7 mm Hg; P < .01) and 13 to 15 years of age (61 +/- 8; P < .01 mm Hg). The changes with age were not significant for white subjects. CONCLUSION: These results provide age-specific reference data for ABPM in youths. These values differ by sex (boys more than girls) and race (Blacks more than Whites).

Ambulatory blood pressure and renal function in healthy children and adolescents.

Our previous studies using noninvasive ambulatory blood pressure (ABP) monitoring demonstrated racial differences in the diurnal pattern of blood pressure (BP), with higher nighttime BP for African-Americans than for Anglo-Americans despite similar daytime BP. We have hypothesized that the increased BP load in African-Americans contributes to the increased prevalence of hypertension and BP-induced target organ damage in adults. The purpose of this study was to examine the relationship between ABP patterns and renal function in healthy, normotensive black and white youths. The subjects were 22 African-American and 28 Anglo-American children and adolescents aged 10 to 18 years. Renal function was estimated by creatinine clearance (CCr). The African-American and Anglo-American subjects were similar in age, gender composition, casual BP, and CCr. The relationship between CCr and BP was not significant for casual BP or daytime BP for either group, or with nighttime BP in the Anglo-American subjects. In contrast, CCr was related negatively to both nighttime systolic BP (r = -0.47, beta = -1.21; P < .02) and nighttime diastolic BP in the African-American subjects (r = -0.45, beta = -2.13; P < .03). These results are consistent with our hypothesis.

Ambulatory blood pressure patterns in youth.

We examined the influence of sex, race, and age on ambulatory blood pressure (BP) patterns in youths. The subjects were 300 normotensive, healthy adolescents between the ages of 10 and 18 years, including 160 boys and 140 girls, of whom 149 were white and 151 were black. The data were divided into periods of activity (Period I: 8 AM to 10 PM) and inactivity (Period II: 10 PM to 8 AM). Boys had higher systolic BP during both Period I (117 +/- 11 nu 112 +/- 8 mm Hg; P < .05) and Period II (109 +/- 11 nu 106 +/- 10 mm Hg; P < .03). Blacks had higher systolic (108 +/- 10 nu 106 +/- 10 mm Hg; P < .01) and diastolic BP (63 +/- 8 nu 60 +/- 7 mm Hg; P < .003) during Period II. Interactions between race and age were found for both systolic (P < .005) and diastolic (P < .005) BP during Period II. Further analyses indicated associations between age and both systolic (beta = 1.16; P < .001) and diastolic (beta = 1.04; P < .0001) BP in black but not white subjects. An interaction was observed between sex and age for systolic BP during Period II (P < .005), with a relationship for boys (beta = 1.47; P < .001) but not for girls. These results suggest that the black adolescents showed a progressive increase in nocturnal BP with age, a pattern not observed in the white youths. This increased BP load may contribute to the early development of hypertension and BP-induced target organ damage in blacks.

Renin-angiotensin-aldosterone system in healthy subjects aged ten to eighteen years.

We obtained normative data for plasma renin activity (PRA) and plasma aldosterone concentration from a biracial sample of 195 healthy, normotensive children and adolescents aged 10 to 18 years. The sample included 119 boys and 76 girls, of whom 103 were black and 92 were white. The mean PRA value (+/- SD) was 2.52 +/- 1.95 ng/ml per hour, with minimal and maximal values of 0.1 and 13.50 ng/ml per hour. The mean plasma aldosterone concentration was 12.56 +/- 8.59 ng/ml, with minimal and maximal values of 1.6 and 50.1 ng/ml. We also examined the effects of subject characteristics and electrolyte intake. The slope relating sodium excretion to PRA was negative and highly significant (slope = -0.01; p < 0.003). The slope relating PRA to plasma aldosterone concentration was positive and highly significant (slope = 1.59; p < 0.0001). We did not observe differences in either variable as a function of age, sex, race, or family history of hypertension. These results suggest that differences based on race and family history of hypertension observed in adults are not present in youth.

Sodium excretion and racial differences in ambulatory blood pressure patterns.

The influence of Na+ excretion and race on casual blood pressure and ambulatory blood pressure patterns was examined in a biracial sample of healthy, normotensive children and adolescents (10-18 years; n = 140). The slopes relating 24-hour urinary Na+ excretion to systolic blood pressure were different for both black and white subjects for casual blood pressure (p less than 0.001) and blood pressure during sleep (p less than 0.03). For casual blood pressure, the slope was significant for black subjects (beta = 0.17; p less than 0.001) but not for white subjects. For blood pressure during sleep, the slope was again significant for black subjects (beta = 0.08; p less than 0.01) but not for white subjects. Na+ excretion was also related to awake levels of systolic blood pressure for black subjects (beta = 0.08, r = 0.36; p less than 0.01), although the slopes for both black and white subjects were not significantly different. Further analyses indicated the results were not due to racial differences in 24-hour urinary K+ excretion. However, plasma renin activity was marginally related to Na+ excretion in white subjects (r = 0.22; p less than 0.06) but not black subjects, a finding that is consistent with previous studies. Na+ excretion was not associated with diastolic blood pressure or heart rate in either group under any condition. The results of this study support research that has demonstrated a stronger relation between Na+ handling and casual blood pressure in black subjects and extend these findings to blood pressure while the subject is both awake and asleep.

Patterns of sodium excretion during sympathetic nervous system arousal.

The purpose of this study was to examine Na+ handling and regulation during 1 hour of behaviorally induced sympathetic nervous system (SNS) arousal followed by 2 hours of recovery. Two patterns of response were observed among experimental subjects, despite similar changes in blood pressure and heart rate. In one group (n = 19), Na+ excretion increased significantly during SNS arousal, which then decreased significantly during recovery (12.3 versus 16.0 versus 13.1 meq/hr, baseline, SNS arousal, recovery, respectively). Changes in Na+ excretion were correlated with changes in creatinine clearance from baseline to SNS arousal (r = 0.54) and SNS arousal to recovery (r = 0.58), and were accompanied by significant increases in plasma renin activity (1.5 versus 2.0 ng/ml/hr) and aldosterone (8.5 versus 10.3 ng/ml/hr) from baseline to SNS arousal. Na+ excretion decreased during SNS arousal in the other group of subjects (n = 17) and remained below baseline levels during recovery (16.2 versus 12.7 versus 11.9 meq/hr). These changes were associated with significant decreases in creatinine clearance from baseline to recovery (138 versus 121 ml/min/1.73 m2) and significant increases in plasma renin activity from baseline to SNS arousal (1.3 versus 2.2 ng/ml/hr) but not in aldosterone. Control subjects (n = 24) maintained baseline levels of each variable throughout the procedure. These results suggest that individuals differ in Na+ handling and regulation during behavioral arousal. Decreases in Na+ have been reported previously in humans and animals at risk for the development of hypertension.

Ambulatory blood pressure patterns in children and adolescents: influence of renin-sodium profiles.

A renin-sodium nomogram for normotensive children and adolescents was developed at our institution. The ambulatory blood pressure patterns of subjects classified by the nomogram were then compared. A biracial sample of 159 children and adolescents were classified as having a low, intermediate, or high renin-sodium profile based on the relationship between their plasma renin activity and 24-hour urinary sodium excretion. Casual (106/58 vs 107/61 vs 106/62 mm Hg) and awake (116/69 vs 117/69 vs 116/70 mm Hg) blood pressure values were comparable among subjects with low, intermediate, and high renin-sodium profiles. Subjects with high renin-sodium profiles, however, had a smaller decline in systolic blood pressure with sleep than did subjects with low renin-sodium profiles (7 vs 11 mm Hg; P less than .04), and higher diastolic blood pressure readings during sleep than subjects with intermediate renin-sodium profiles (65 vs 62 mm Hg; P less than .05). Subjects with high renin-sodium profiles also had greater variance of diastolic blood pressure readings during sleep than either subjects with low renin-sodium profiles (P less than .01) or those with intermediate renin-sodium profiles (P less than .02). The blunted nocturnal decline and increased nocturnal variance of blood pressure among subjects with high renin-sodium profiles may be a marker or mechanism for the future development of essential hypertension.

Calcium sensitivity of vertebrate skeletal muscle myosin.

The calcium sensitivity of vertebrate skeletal muscle myosin has been investigated. Adenosinetriphosphatase (ATPase) activity was assayed in a reconstituted system composed of either purified rabbit myosin plus actin or myosin plus actin, tropomyosin, and troponin. The calcium sensitivity of actomyosin Mg-ATPase activity was found to be directly affected by the ionic strength of the assay medium. Actomyosin assayed at approximately physiological ionic strength (120 mM KCl) demonstrated calcium sensitivity which varied between 6 and 52%, depending on the myosin preparation and the age of the myosin. Mg-ATPase activity was increased when calcium was present in the assay medium at physiological ionic strength. Conversely, actomyosin Mg-ATPase activity assayed at a lower ionic strength (15 mM KCl) was inhibited by addition of calcium. Addition of tropomyosin and troponin to the assay increased the calcium sensitivity of the system at the physiological ionic strength still further (up to 99% calcium sensitivity) and conferred calcium sensitivity on the system at the lower ionic strength (greater than 90% calcium sensitivity). A correlation also existed between myosin's calcium sensitivity and the phosphorylated state of light chain 2.

Degenerative changes at the neuromuscular junctions of red, white and intermediate muscle fibers. Part 1. Response to short stump nerve section.

Degeneration at the neuromuscular function following cutting the phrenic nerve at the 9th intercostal space differs in red, white and intermediate skeletal muscle fibers. The ultrastructure of the nerve terminal and the muscle fiber between 12 hours and 21 days following denervation suggests that lack of neurotrophic influences results in responses specific for each fiber type. Degeneration of axon ends is rapid and by 2 days axon terminals are missing from the end-plate areas of all 3 fiber types. Schwann cells "engulf" degenerating axon terminals and eventually replace them in the primary clefts. Schwann cells display specific morphological changes directly related to axonal degeneration. In all instances axon terminal degeneration precedes muscle fiber degeneration. Synaptic cleft changes are similar for all types of muscle fibers. Primary cleft structure appears to be dependent upon neurotrophic influence, whereas secondary cleft structure is relatively unaffected by denervation. Initial changes in subsynpatic regions of muscle fibers include focal loss of sarcomere alignment and skewing of the Z lines. By 21 days myofibrillar disorganization appears most severe in white fibers and least in red muscle fibers. The rate and degree of degeneration of the axon terminal and subjacent muscle fiber are different for each of the 3 muscle fiber types.

Degenerative changes at the neuromuscular junctions of red, white, and intermediate muscle fibers. Part 2. Responses to long stump nerve section and colchicine treatment.

The ultrastructure at the neuromuscular junction (NMJ) of red, white, and intermediate skeletal muscle fibers undergoes specific changes following either unilateral severance of the phrenic nerve or unilateral topical treatment of the phrenic nerve with colchicine. Both procedures were performed in the cervical region and produce similar rates of muscle fiber degeneration. The severity of degeneration appears to be related to muscle fiber type with white fibers being most severely affected and red fibers least affected. Degeneration rates of the axon terminal also correlate with fiber type in the orderwhite, intermediate, red. However, the rates of degeneration of the specific axon terminals are more rapid with surgical severance than with colchicine treatment. Statistical analysis of morphometric data indicates that hemidiaphragms denervated surgically exhibited significant axon terminal degeneration before significant muscle degeneration. Conversely, diaphragmatic muscle fibers of colchicine-treated phrenic nerves exhibit significant degeneration before loss of the axon terminal. Despite reversal of the temporal sequences for loss of axonal and muscular components between the two preparations, degenerative characteristics of muscle fiber structure are similar. This suggests that the presence of fiber-specific neurotrophic substances transmitted from the neuronal cell body to the axon terminal and released at the NMJ may be an important factor in the maintenance of normal muscle fiber morphology.