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Biomedical subjects

R Dietz

Publications and source records attributed to R Dietz.

354 records · Page 20Linked to original sources
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Intracranial amebic abscesses: CT and MR findings.

The CT and magnetic resonance findings in a case of intracranial amebic abscesses are described. Due to increased travel to endemic areas, amebic abscess should also be included in the differential diagnosis for patients who live in the temperate parts of the world.

Animals↗
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Salt loss as a possible mechanism eliciting an acute malignant phase in renal hypertensive rats.

1. The acute malignant phase of hypertension in rats with an untouched contralateral kidney is characterized by salt and fluid loss, increased fluid intake, decrease in body-weight gain, and reduced food consumption. Plasma concentrations of sodium and potassium were reduced, and plasma angiotensin II rose to about four times normal. 2. To investigate the significance of an untouched contralateral kidney for the development of the acute malignant phase in renal hypertensive rats, comparative studies were undertaken in unilaterally nephrectomized rats with stenosis of the remaining renal artery and in rats with bilateral renal artery stenosis. In addition, the effect of declamping one renal artery in rats with bilateral stenosis was studied. 3. In unilaterally nephrectomized rats, no signs of sodium and fluid loss were demonstrable, despite marked increase in blood pressure. Similarly, rats with bilateral renal artery stenosis had no acute malignant phase of hypertension. 4. In hypertensive rats with bilateral stenosis, removal of the clip from one renal artery was followed by an immediate fall in blood pressure and a subsequent gradual increase. Eleven of sixteen rats lost salt and fluid and developed an acute malignant phase. Plasma angiotensin II was high and serum urea elevated. 5. Consumption of 2% saline in addition to water as drinking fluid had a beneficial effect, since only five of fourteen rats showed signs of the acute malignant phase, which were milder than in rats on water only. 6. It is concluded that the untouched contralateral kidney is responsible for the negative salt and water balance and its consequences, which are characteristic of the acute malignant phase of experimental renal hypertension.

Animals↗
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Fluid and salt intake during the development of renal hypertension in rats.

1. In Sprague-Dawley rats, two-kidney, one-clip renal hypertension was induced, and the drinking behaviour as well as total fluid and sodium intake were studied before and for 16 days after the operation. 2. When water alone was offered as drinking fluid, the blood pressure reached values that were by about 20 mmHg higher than those in the rats which had free choice of drinking water or 2% saline. 3. In those rats which had water and 2% saline to drink, the total sodium and fluid intake rose transiently for three days, as compared with that of the sham-operated controls, and increased steeply starting from the 7th and 10th day, respectively. When a tighter stenosis of the renal artery was induced, the pressure rose more rapidly, and the total fluid and sodium intake increased continuously after the operation until the end of the experiment. 4. A positive correlation was demonstrable between the height of blood pressure and the total daily intake of fluid and sodium, respectively. 5. The relation between the total daily fluid and the total daily sodium intake followed a straight regression line. 6. The hypertensive rats which had a high total sodium intake responded to the withdrawal of the 2% saline solution, within 2 days, with increased water intake, decreased food intake, and loss of body weight, whereas the blood pressure remained high. 7. In the two-kidney, one-clip hypertension, no 'critical level of blood pressure' can be defined, beyond which the contralateral kidney starts to lose sodium.

Animals↗
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Effects of neonatal sympathectomy by 6-hydroxydopamine on blood pressure and intravascular volume in young stroke-prone spontaneously hypertensive rats.

1. Stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar Kyoto rats (WKY) were 'chemically sympathectomized' immediately after birth with 6-hydroxydopamine (6-OHDA, 100 mg/kg s.c. daily) for the first 10 days of life. 2. Body weight gain was diminished in both groups as compared with sham-treated controls. Blood pressure was reduced in 'sympathectomized' SHRSP, and also WKY rats had a slightly lower blood pressure than control rats. 3. Plasma concentration of angiotensin II and renin content of the kidney were not influenced by 6-OHDA. 4. 'Sympathectomized' SHRSP retained similar amounts of sodium than sham-treated SHRSP when sodium retention is expressed per body weight gained. Plasma and blood volumes were increased in both SHRSP and WKY rats, whereas packed cell volume was significantly decreased. 5. These results demonstrate the significance of an intact sympathetic nervous system for the development of hypertension in SHRSP. The expanded plasma and blood volume in 'sympathectomized' rats indicate an important role of the sympathetic nervous system and/or the arterial blood pressure for the regulation of intravascular volume.

Angiotensin II↗
PubMedDate not supplied

Growth hormone treatment in dilated cardiomyopathy.

Treatment with human recombinant growth hormone (GH) has yielded conflicting results in patients with congestive heart failure. We analyzed the baseline somatotrophic axis in 50 patients with dilated cardiomyopathy. Then, a double-blind, randomized, placebo-controlled study of GH was performed. We randomly allocated these patients to treatment with subcutaneous GH (2 IU daily) or placebo for a minimum of 12 weeks. The primary end-points were the effect on left ventricular (LV) mass and systolic wall stress. The secondary endpoint was LV ejection fraction. Severity of heart failure as determined by cardiac index, LV end-diastolic diameter, and plasma noradrenaline concentrations correlated markedly with baseline serum insulin-like growth factor-1 (IGF-1) levels. Patients in the GH group had an increase in LV mass compared with the placebo group (p = 0.0001). There was no significant difference in LV systolic wall stress, mean blood pressure, or systemic vascular resistance between the two groups. New York Heart Association (NYHA) functional classification and distance in 6-minute walk test remained unchanged. The change in IGF-1 concentrations between GH and placebo group was notably related (p = 0.0001) to the change in LV mass (p = 0.0001). The GH-induced increase of IGF-1 predicted the changes of ejection fraction (p < 0.05). A marked increase of ejection fraction of 7% was observed in patients whose IGF-1 increased by more than the median increase, in comparison to the patients with an increase below the median (p = 0.03). Serum levels of IGF-1 reflecting GH secretion are diminished in relation to severity of heart failure in patients with dilated cardiomyopathy. GH-induced increases of IGF-1 of more than 80 pg/mL caused notable improvement of ejection fraction. There is a marked increase in LV mass in patients with dilated cardiomyopathy given GH. Changes in LV mass are related to changes in serum IGF-1 concentrations.

Biomarkers↗
PubMedDate not supplied

Contribution of the sympathetic nervous system to the hypertensive effect of a high sodium diet in stroke-prone spontaneously hypertensive rats.

In stroke-prone spontaneously hypertensive rats (SHRSP) plasma norepinephrine levels and vascular reactivity to norepinephrine are increased and intravascular volume is reduced during the developmental phase of hypertension. Since the accelerated rise in blood pressure following sodium-loading in SHRSP cannot be attributed to the volume-retaining properties of sodium, the effects of an increased dietary intake of sodium on biochemical parameters of sympathetic vascular tone were investigated. The following results were obtained. First, the increased reactivity of vascular smooth muscle was further augmented in sodium-treated SHRSP; the degree of supersensitivity was positively correlated to the plasma sodium concentration. After blockade of the neuronal uptake by 30 microM cocaine, no difference in vascular reactivity to norepinephrine was detected between SHRSP on a normal and SHRSP on a high-sodium diet. Second, the inactivation of norepinephrine by the neuronal uptake was impaired in rats on a high-sodium diet, the impairment being more pronounced in SHRSP than in Wistar-Kyoto (WKY) rats. This decreased inactivation could be expected to cause higher concentrations of the neurotransmitter at the receptor site if the transmitter release from the nerve ending remains constant. Third, the release of norepinephrine and epinephrine into the plasma was increased in sodium-loaded SHRSP but not in sodium-loaded WKY. Cold exposure exaggerates these differences between normotensive and hypertensive rats. These findings suggest that a high-sodium intake modifies the transmission of sympathetic impulses at the level of the nerve terminal in both WKY and SHRSP. In the normotensive rats, moderate impairment of norepinephrine inactivation, however, was balanced by an appropriate reduction in central sympathetic discharge following sodium-loading. In the hypertensive rats, the peripheral disturbance in norepinephrine inactivation due to sodium-loading was obviously not balanced by an adequate withdrawal of central sympathetic discharge. The resultant hemodynamic change was a further increase in the sympathetically mediated vasoconstriction, which is regarded as at least one of the main mechanisms of the sodium-dependent acceleration of hypertension in SHRSP.

Animals↗
PubMedDate not supplied

Development of a new strain of spontaneously hypertensive rats homozygous for hypothalamic diabetes insipidus.

The aim of the present study was to investigate whether the presence of arginine vasopressin (AVP) is necessary for the establishment of high blood pressure in spontaneously hypertensive rats (SHR). For this purpose we crossbred SHR of the stroke-prone substrain (SHRSP) with rats homozygous for hypothalamic diabetes insipidus of the Brattleboro strain (DI) which are unable to synthetize AVP. The successful introduction of the DI gene into the SHRSP strain (SHRDI) was demonstrated by the following observations: In 10-month-old rats, water intake was similarly elevated in SHRDI as in DI rats (137 +/- 6.5 vs 125 +/- 10.5 ml per 24 hours). AVP was undetectable in the plasma, in the hypothalamus, and in the pituitary of SHRDI and DI rats. Urine osmolality and urinary concentration of sodium and potassium were markedly reduced. SHRDI and DI did not adequately concentrate their urine during an 8-hour period of water deprivation, but both strains of rats responded well with a fall in urine output and a rise in urine osmolality to subcutaneous administration of the non-pressor analog of AVP, DDAVP. Mean arterial blood pressure was markedly increased in SHRDI as well as in SHRSP (184 +/- 9.7 vs 197 +/- 5.2 mm Hg). Thus, we have developed a new line of spontaneously hypertensive rats homozygous for hypothalamic diabetes insipidus. From this finding it is concluded that AVP is not essential for the development and maintenance of spontaneous hypertension of rats.

Animals↗