Volume expansion natriuresis during servo control of systemic blood pressure in conscious dogs

The importance of arterial blood pressure (BP) and ANG II for the renal natriuretic response (NaEx) to volume expansion (3.5% body wt) was investigated during converting enzyme blockade (enalaprilate, 2 mg/kg). In separate experiments, BP was clamped either 30 mm Hg above or a few millimeters mercury below baseline by servo-controlled infusion of ANG II or sodium nitroprusside, respectively, so that volume expansion did not change BP. Enalapril decreased BP by 8 mm Hg. Without clamping, volume expansion returned BP to that of preenalapril control and increased NaEx 10-fold (40+/-10 to 377+/-69 micromol/min). During high pressure clamping (133+/-2 mm Hg), peak NaEx after volume expansion was 6% of control experiments. During low pressure clamping, NaEx was 68% of control experiments (45+/-15 to 256+/-64 micromol/min). The results show that 1) in absence of ANG II, volume expansion elicited pronounced natriuresis without increases in BP beyond baseline, 2) in the presence of hypertensive amounts of ANG II, the volume expansion-induced natriuresis was almost eliminated, and 3) nitroprusside prevented the increase in BP but not sodium excretion during volume expansion. ANG II appears to dominate the control of NaEx; however, when absent, volume expansion may still induce marked natriuresis even at constant BP, possibly via nitric oxide-mediated mechanisms.     

Impact of acute hypoxia on heart rate and blood pressure variability in conscious dogs

To examine whether the impacts of hypoxia on autonomic regulations involve the phasic modulations as well as tonic controls of cardiovascular variables, heart rate, blood pressure, and their variability during isocapnic progressive hypoxia were analyzed in trained conscious dogs prepared with a permanent tracheostomy and an implanted blood pressure telemetry unit. Data were obtained at baseline and when minute ventilation (VI) first reached 10 (VI10), 15 (VI15), and 20 (VI20) l/min during hypoxia. Time-dependent changes in the amplitudes of the high-frequency component of the R-R interval (RRIHF) and the low-frequency component of mean arterial pressure (MAPLF) were analyzed by complex demodulation. In a total of 47 progressive hypoxic runs in three dogs, RRIHF decreased at VI15 and VI20 and MAPLF increased at VI10 and VI15 but not at VI20, whereas heart rate and arterial pressure increased progressively with advancing hypoxia. We conclude that the autonomic responses to isocapnic progressive hypoxia involve tonic controls and phasic modulations of cardiovascular variables; the latter may be characterized by a progressive reduction in respiratory vagal modulation of heart rate and a transient augmentation in low-frequency sympathetic modulation of blood pressure.     

Comparison of direct and indirect blood pressure measurement in anesthetized dogs.

This study was conducted to determine whether blood pressures and pulse rate could be determined accurately by indirect measurements from the front and hind legs of 15- to 40-kg dogs anesthetized with isoflurane. Indirect measurements from each animal were compared to direct measurements obtained from a catheter placed into the abdominal aorta via the femoral artery at four ranges of systolic pressure. When systolic pressure was above 80 mm Hg, indirect measurements were either the same as direct measurements or slightly lower. However, when systolic pressures were below 80 mm Hg, indirect systolic pressure measurements were 6 to 15% higher than direct measurements. Larger differences in diastolic pressures were found, which resulted in differences in mean pressure. The most accurate measurements were found when the cuff width-to-limb circumference ratio was between 0.4 and 0.6 and when systolic pressure was between 80 and 100 mm Hg.     

A rapid simple procedure for direct measurement of excreted thiamine from yeast

A new rapid method for the detection of extracellular thiamine production in yeast is described. This method is based on a modified thiochrome assay where fluorescent zones surrounding thiamine excretor colonies can be directly visualized under UV light on agar plates. This new procedure is simple to perform on a large number of colonies simultaneously and results can be obtained within minutes.     

A simple procedure for NMR measurements of intra- and extracellular sodium in intact tissues

The total Na+ and both the intra- and extracellular Na+ content of excised rat and frog tissues was quantitated by 23Na NMR at 95.51 MHz. An external capillary containing 33 mM Na7[Dy(P3O10)2], resonating about 30 ppm upfield relative to the 0.00 ppm of the intracellular Na+, was inserted into the tissues. The capillary was calibrated against a concentration range of pure NaCl solution, for measurement of intracellular Na+, and against the same concentrations of NaCl solutions containing 4-6 mM K7[Dy(P3O10)2] in 50 mM histidine. Cl and 100 mM choline. Cl, for measurement of extracellular Na+. Spectra were recorded on tissues first in the absence of the shift reagent for determination of the total Na+. After addition of a K7[Dy(P3O10)2] solution to the sample, the 23Na spectra were recorded immediately so that data accumulation was completed within 15 min. Under these conditions, the extracellular Na+ resonated from 10 to 20 ppm upfield relative to the intracellular Na+, and no loss in the intensity of the extracellular Na+ resonance occurred due to the lability of dysprosium(III)tripolyphosphate (cf. Matwiyoff et al., Magn. Reson. Med. 3: 164, 1986). The intra- and extracellular Na+ content of the tissue was calculated from the integrated areas of the respective Na+ resonances and that of the calibrated capillary, from the known weight of the tissue, and from the known volumes of the solutions added.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chronic propranolol treatment decreases pulmonary artery pressure in conscious dogs

Daily administration of propranolol to 9 chronically instrumented, trained dogs for 2 weeks caused significant (p less than 0.05) decreases in heart rate (70 +/- 8 to 57 +/- 6 beats/min), cardiac output (3.6 +/- 0.3 to 2.9 +/- 0.2 liters/min), pulmonary arterial pressure (15.7 +/- 0.5 to 10.0 +/- 0.5 mm Hg) and total pulmonary vascular resistance (4.6 +/- 0.6 to 3.3 +/- 0.4 units). Nadolol, a structurally dissimilar beta-adrenergic receptor antagonist, caused a similar decrease in total pulmonary resistance. Acute meclofenamate administration did not return to normal pulmonary arterial pressure and resistance in the dogs chronically treated with beta-adrenergic receptor blockers. We therefore conclude that chronic beta-adrenergic receptor blockade lowered pulmonary arterial pressure and resistance by a mechanism independent of cyclooxygenase. In addition, chronic beta-adrenergic receptor blockade did not affect the potential for hypoxic vasoconstriction.