David P. Penney

Ultrasound Enhancement of Rabbit Femoral Artery Thrombolysis

Experiments were conducted to evaluate the potential of low-intensity, externally applied ultrasound to accelerate arterial thrombolysis in an animal model and to characterize potential effects of ultrasound exposure on vessel wall morphology. The femoral arteries of 32 rabbits were exposed, a flowprobe was positioned around the vessel, and a stenosis produced with two circumferential silk sutures to reduce flow by 50%. Thrombosis was achieved by injecting thrombin through the cannulated superficial epigastric branch into a 1-cm segment of femoral artery which was isolated for 20 min. Streptokinase was administered intravenously as a 15,000 U/kg bolus followed by an infusion of 15,000 U/kg per h. Ultrasound (1 MHz, 2 W/cm2) was delivered to the thrombosed vessel during streptokinase administration in 17 animals, and 15 control animals received sham ultrasound only. Thrombolysis occurred in nine of 17 (53%) animals receiving both streptokinase and ultrasound, and this was significantly greater than the rate in animals receiving streptokinase alone (2/15, 13%; P=0.025). Ultrasound caused a mean temperature elevation of 4 degrees C in exposed tissues. Light and electron microscopy demonstrated increased platelet accumulation on thrombi in ultrasound-treated vessels compared with controls. Endothelial cell vacuolation was seen by electron microscopy in ultrasound-exposed vessels. The results indicate that externally applied, low-intensity ultrasound can significantly enhance thrombolysis in a rabbit arterial model. Possible adverse effects are minor and include platelet accumulation, temperature elevation and minor endothelial changes. Externally applied ultrasound has potential value as an adjunct to thrombolytic therapy.

The early release of surfactant following lung irradiation of alveolar type II cells

Abstract At 1 hour, 24 hours, and l week following irradiation, studies utilizing LAF 1 /J mouse lung showed increase of disaturated alveolar phosphatidylcholine (PC) by radiolabelling and alveolar lavage, thus indicating PC as a nearly immediate post-irradiation biomarker. A corresponding decrease of PC in lung tissue following alveolar lavage correlated with an early decrease of Iamellar bodies in type II pneumocytes after irradiation.

The influence of contrast agents on hemorrhage produced by lithotripter fields

Ultrasonic contrast agents greatly increase the side effects of low-amplitude lithotripter fields in mice. Using a piezoelectric lithotripter, adult mice were exposed to 200 lithotripter pulses with a peak positive pressure amplitude of 2 MPa. During the exposure period, mice were injected with approximately 0.1 mL of the ultrasonic contrast agent Albunex. For comparison, another group of mice experienced the same lithotripter exposures, but were not injected with contrast agent. Following exposures, animals were sacrificed and observed for hemorrhage in various organs and tissues. Mice exposed to the lithotripter field alone had minimal hemorrhage only in the intestine and lung. In comparison, mice injected with Albunex during exposure exhibited extensive hemorrhage in the intestine, kidney, muscle, mesentery, stomach, bladder, seminal vesicle and fat.

Specific early fine structural changes in the lung following irradiation

Abstract The lungs of mice were irradiated with single and fractionated doses of 1000 R, 2000 R and 3000 R and recovered 1 hr, 1 day, 1 week and 1 month following exposure. Electron microscopy revealed early changes in the decrement of lamellar bodies of Type 11 pneumocytes and increased fibrous content and edema in the septal walls of all animals treated. Those lungs treated with fractionated doses or irradiation displayed more pronounced cellular damage than did singly-dosed lungs. It is proposed that these early changes may predict for subsequent atelectasis.

THRESHOLDS FOR ULTRASONICALLY INDUCED LUNG HEMORRHAGE IN NEONATAL SWINE

The threshold for generation of lung hemorrhage in adult mice by pulsed ultrasound has been shown to be approximately 1 MPa at the surface of the lung (10-microseconds pulse and a carrier frequency of 2 MHz). This investigation used neonatal swine to determine if the findings for mice can be generalized to other species. After exploratory observations, the inverse sampling method was used in a primary study (22 animals, 88 exposure sites) to determine the threshold for lung hemorrhage in neonatal swine. The primary study was followed by a separate confirmation study (13 animals, 48 exposure sites), testing the conclusions of the first study and comparing damage at subthreshold levels with sham-exposed animals. A separate investigation explored the histological nature of tissue damage at suprathreshold levels. A 2.3-MHz focused transducer (10 microseconds at 100-Hz pulse-repetition frequency) was incremented vertically for a distance of 2 cm over the chest of the subject for a total exposure period of 16 min. Animals were euthanized and lungs were scored by visual inspection for numbers and areas of gross hemorrhages. The threshold level for hemorrhage was approximately 1.5 MPa peak positive pressure in water at the surface of the animal or, at the surface of the lung, 1.1 MPa peak positive pressure, 1 MPa fundamental pressure, 0.9 MPa maximum negative pressure, 25 W cm-2 pulse average intensity or a mechanical index of 0.6. These values are essentially the same as those reported for adult mice.

Early and late pulmonary toxicity in mice evaluated 180 and 420 days following localized lung irradiation

The lungs of 2 to 3-month-old female C3H/HeJ and 6-month-old male LAF1 mice were locally irradiated with graded doses of radiation ranging from 900 to 1800 rad. The patterns of animal details for times up to 60 weeks after irradiation were recorded. Over this period mice in all the irradiated groups continued to die. However, the onset of animal deaths was dose dependent such that lethality occurred earlier after the higher radiation doses. Whereas mice receiving large radiation doses started to die by 75-100 days post-treatment, few or no animal deaths occurred in those groups receiving the lowest doses until 200-300 days after irradiation. At 180 and 420 days postirradiation animal lethality dose-response curves were constructed; these were found to be similar in shape (sigmoid), but at the later time the calculated LD/sub 50/ values were approx.300-400 rad lower than those determined using the 180-day post-treatment end point. Histological examination of the irradiated lungs indicated that the animal deaths occurring by 180 days were associated with radiation pneumonitis while the late deaths were associated with pulmonary fibrosis. The addition of the radiation sensitizer misonidazole prior to lung irradiation did not significantly enhance pulmonary toxicity at either end point.

Age dependence of ultrasonically induced lung hemorrhage in mice.

Thresholds for ultrasonically induced lung hemorrhage were determined in neonatal mice (24-36 h old), juvenile mice (14 d old) and adult mice (8-10 weeks old) to assess whether or not the threshold for lung hemorrhage is dependent upon age. Ultrasonic exposures were at 1.15 MHz with a pulse length of 10 microseconds, pulse repetition frequency of 100 Hz and a total exposure duration of 3 min. The threshold for lung hemorrhage occurred at a peak positive acoustic pressure of approximately 1 MPa for mice in all three age groups. Although the thresholds were similar for neonatal, juvenile and adult mice, the sizes of the suprathreshold hemorrhages were significantly larger in adult mice than in neonatal or juvenile mice.

Surfactant release as an early measure of radiation pneumonitis

The immediate release of surfactant into lung alveoli following irradiation has been studied as a potential indicator for the later development of radiation pneumonitis. Utilizing single dose radiation exposure to the whole thorax in male LAF1/J mice, steep dose response curves for lavaged alveolar surfactant were identified at 7 and 28 days after exposure. Seven days after irradiation there was no elevation with doses up to and including 12 Gy; above this dose a detectable increase occurred. At 28 days the surfactant recovered by lavage was elevated compared to the levels seen at day 7 for all doses; doses greater than 12 Gy produced surfactant values significantly greater than those found in mice treated with 12 Gy or less. The radiation pulmonary lethality dose response curve assessed four months later indicated an LD50 value of approximately 13 Gy. The early biochemical effect and the later radiation pneumonitis lethalities therefore closely coincided. The evidence strongly indicates that alveolar surfactant release uncovered hours to days after radiation exposure may be an early biochemical marker that predicts for subsequent pneumonitis radiation injury.

Remnants of Albunex® nucleate acoustic cavitation

Mice were injected with 0.1 mL Albunex and exposed to 200 pulses from a piezoelectric lithotripter at times ranging from 5 min to 24 h following injection. Each pulse was approximately 1.5 sinusoidal oscillations at a fundamental frequency of approximately 0.1 MHz with pressure amplitude of approximately 2 MPa. Although the contrast agent ceases to be an effective scatterer of diagnostic ultrasound after a few minutes in the circulation, the modest lithotripter exposures caused significant hemorrhaging in bladder, mesentery and intestine for periods of up to 4 h after injection. The results demonstrate either that highly stable bubbles much smaller than resonance size or air-containing fragments of the shells of Albunex serve as effective nuclei for acoustic cavitation.

Diazepam receptor: Specific binding of [3H]diazepam and [3H]flunitrazepam to rat brain subfractions

Evidence is beginning to accumulate that specific molecules bind the benzodiazepines in a receptorrelated manner [l-4]. However, to date, no studies have demonstrated to which cellular structures the diazepam was bound. Morphologic confirmation is essential when one is dealing with the central nervous system, since ‘standard’ fractionation procedures for one area in the brain give varying results in other regions of the brain [5]. We report here that the fraction of rat forebrain containing synaptic junctions binds specifically [3H]diazepam; furthermore, we show that [3H]flunitrazepam binds to the benzodiazepine ‘receptors’ with more than IO-times greater affinity in the described system than [3H]diazepam and hence may be a useful tool for further investigation.