Extraction of water labeled with oxygen 15 during single-capillary transit. Influence of blood pressure, osmolarity, and blood-brain barrier damage.

By external detection, the influence of arterial blood pressure (BP), osmolarity, and cold-induced blood-brain barrier damage was assessed on the extraction of water labeled with oxygen 15 during single-capillary transit in the rat. There was an inverse relation between arterial BP and extraction that was attributable to the influence of arterial BP on cerebral blood flow (CBF) and the relation between CBF and extraction. Neither arterial BP nor osmolarity of the injected bolus had any direct effect on extraction of water 15O, signifying that the diffusional exchange component (determined by blood flow) of extraction greatly surpasses the convection flow contribution by hydrostatic or osmotic forces. Damage to the blood-brain barrier did not change its permeability to water.

Chemiluminescence-linked immunoassay.

Covalent complexes of a chemiluminescent compound (a luminol derivative), protein and a steroidal hapten have been used as a labelled antigen in a way analogous to the radioactive label in radioimmunoassay. The antibody-bound complex emits light when treated with hydrogen peroxide and copper acetate at high pH. The chemiluminescent complex bound to antibody can be displaced by free steroid to produce a standard curve in a way analogous to radioimmunoassay.

A rotating double-headed positron camera.

Based on a double-headed rotating uncollimated scintillation camera system, a positron imaging device was developed. After a rotating data acquisition in coincidence mode, 16 transverse section images are reconstructed by back projection. To obtain a uniform response, a limited angle reconstruction option is incorporated in this process. After correction for the system response by a three-dimensional deconvolution technique, the 16 transverse section images are stored on disk as a standard patient study for further analysis. The system can also be operated in a stationary mode. In this mode longitudinal tomographic images are obtained. Return to single photon scintigraphy is possible by remounting the collimators and by switching off the coincidence electronics.

Comparison of L-[1-11C]methionine and L-methyl-[11C]methionine for measuring in vivo protein synthesis rates with PET.

To evaluate the feasibility of using either L-[1-11C]-methionine or L-[methyl-11C]methionine for measuring protein synthesis rates by positron emission tomography (PET) in normal and neoplastic tissues, distribution and metabolic studies with 14C- and 11C-labeled methionines were carried out in rats bearing Walker 256 carcinosarcoma. The tissue distributions of the two 14C-labeled methionines were similar except for liver tissue. Similar distribution patterns were observed in vivo by PET using 11C-labeled methionines. The highest 14C incorporation rate into the protein-bound fraction was found in the liver followed by tumor, brain, and pancreas. The incorporation rates in liver and pancreas were different for the two methionines. By chloroform-methanol fractionation of these four tissues, in liver significantly different amounts of 14C were observed in macromolecules. Also in brain tissue slight differences were found. By HPLC analyses of the protein-free fractions of plasma, tumor, and brain tissue at 60 min after injection, for both methionines several 14C-labeled metabolites in different amounts, were detected. About half of the 14C-labeled material in the protein-free fraction was found to be methionine. In these three tissues the amount of nonprotein metabolites and [14C]bicarbonate amount ranged from 10% to 17% and 12% to 15% for L-[1-14C]methionine and L-[methyl-14C]methionine, respectively. From these results it can be concluded that the minor metabolic pathways have to be investigated in order to quantitatively model the protein synthesis by PET.

Metabolic studies with L-[1-14C]tyrosine for the investigation of a kinetic model to measure protein synthesis rates with PET.

To evaluate a kinetic model for measuring protein synthesis rates by positron emission tomography (PET) in neoplastic and normal tissue, metabolic studies with L-[1-14C]tyrosine were carried out. As an animal model, rats bearing Walker 256 carcinosarcoma were used. Within 60 min after injection, several metabolic parameters were measured. The highest radioactivity uptake, expressed as the differential absorption ratio, was found in pancreas, followed by liver, tumor, and brain. A rapid decarboxylation was observed during the first 15 min. After 60 min, 7.4% of the total injected 14C was expired as 14CO2. In plasma a significant amount of [14C]bicarbonate was detected, but in tissue the amount was negligible. Protein incorporation increased with time. The incorporation rate was the highest in the liver followed by pancreas, tumor, and brain tissues. At 60 min after injection, more than approximately 80% of the 14C in tissue was protein bound. In plasma after a rapid clearance during the first 15 min, the total 14C level increased rapidly and paralleled the increase of protein-bound 14C. As nonprotein [14C]metabolites, in plasma, tumor and brain tissues, p-hydroxyphenylpyruvic acid, p-hydroxyphenyllactic acid, and unidentified metabolites were observed by high performance liquid chromatography. The formation of 14C-labeled 3,4-dihydroxyphenylalanine was found to be negligible. The total amount of these nonprotein metabolites increased with time. At 60 min after injection the percentages of the total nonprotein metabolites and [14C]bicarbonate were only 5.0%, 1.9%, and 3.7% in plasma, tumor and brain tissue, respectively. From our data it is concluded that [11C]carboxylic-labeled tyrosine would be a suitable radiopharmaceutical for measuring protein synthesis rates in neoplastic and normal tissue by PET.

Some experience with 57Co-labeled bleomycin as a tumor-seeking agent.

Bleomycin labeled with 57Co was used as a tumor-localizing agent in 132 patients. In patients with pulmonary tumors the primary localization concentrated radioactivity in 52 of the 54 appropriate cases; out of the 22 clinically known metastases, 19 were visible on the scan; 40 unknown metastases especially in hilus and mediastinum were found by the method and subsequently confirmed. In 22 patients with malignant lymphomas, 18 out of 22 known pathologic lymph glands above the diaphragm were visible on the scan; below the diaphragm the results of scanning in lymph glands and spleen were disappointing, probably because of the disturbing concentration of radioactivity in the kidneys, the bladder, the liver, and sometimes the gut. In 25 patients with various other tumors, 16 out of 22 known localizations above the diaphragm were visible; 2 were uncertain and 4 negative. Below the diaphragm the results were usually negative. In 24 patients with benign lesions, uptake of 57Co-bleomycin was visible on the scintigram in 4 patients with cavitating pulmonary tuberculosis, in 2 with pulmonary infections, in 1 with Caplan lesions of rheumatoid arthritis in the lung, and in 1 with sinusitis ethmoidalis. The significance of these results is discussed.

Radiotracers binding to estrogen receptors: I: Tissue distribution of 17 alpha-ethynylestradiol and moxestrol in normal and tumor-bearing rats.

Ethynylestradiol and moxestrol can be labeled with carbon-11 by introducing this positron emitter in the 17 alpha-ethynyl group. To investigate their potential as radiotracers binding to estrogen receptors, we studied the tissue distribution of tritiated ethynylestradiol and moxestrol, with specific activities of 57 Ci/mmol and 77-90 Ci/mmol, respectively, in the adult female rat. At 30 min after injection, both compounds showed specific uptake in the uterus (% dose/g): 2.52 for ethynylestradiol and of 2.43 for moxestrol. A decrease of the specific activity to 6-9 Ci/mmol resulted in uterine uptakes of 1.60 and 2.10 respectively, for ethynylestradiol and moxestrol, at 30 min. In the female rat bearing DMBA-induced mammary tumors, specific uptake was also measured in the tumors, although the values were only 25-30% of the uterine uptake. Moxestrol showed a greater uptake selectivity in the tumors compared with ethynylestradiol. From this study we conclude that ethynylestradiol and moxestrol have good potential as tracers binding to mammary tumors that contain estrogen receptors.

Estrogen receptor binding radiopharmaceuticals: II. Tissue distribution of 17 alpha-methylestradiol in normal and tumor-bearing rats.

Tritiated 17 alpha-methylestradiol was synthesized to investigate the potential of the carbon-11-labeled analog as an estrogen-receptor-binding radiopharmaceutical. In vitro, 17 alpha-methylestradiol is bound with high affinity to the cytoplasmic estrogen receptor from rabbit uterus (Kd = 1.96 x 10(-10)M), and it sediments as an 8S hormone-receptor complex in sucrose gradients. The compound shows specific uptake in the uterus of the adult rat, within 1 hr after injection. After 30 min the uterine uptake was 1.73% dose/g. In female rats bearing DMBA-induced tumors, specific uterine and tumor uptakes were observed, although at 30 min the tumor uptake was only 23-30% of the uptake in the uterus. Tritiated 17 alpha-methylestradiol with a specific activity of 6 Ci/mmole showed a similar tissue distribution. Our results indicate that 17 alpha-methylestradiol is promising as an estrogen-receptor-binding radiopharmaceutical.

An improved method for the analysis of xenon-133 washin and washout curves.

A method is described for analysis of xenon-133 washin and washout curves, in the presence of a slowly varying background. The method uses least-squares fitting of a single exponential together with a quadratic function to correct for the background. The method has been applied both to simulated data and to data from 25 patients. The accuracy in the relevant lung parameters was 5% over a wide range of the specific ventilation. A comparison is made with other methods in use to measure regional lung-function parameters. Our method produces reliable results even when specific ventilation is low, which can occur in patients with chronic airflow obstruction, where other methods may incur errors of more than 45%.

Nitrogen-13 and xenon-133 ventilation studies.

Due to the solubility of xenon-133 in blood and tissues, errors are introduced in the determination of regional pulmonary ventilation. We investigated these errors by comparing the results from ventilation measurements with Xe-133 and N-13 in five normal subjects (both at rest and during exercise) and in seven patients after a pneumonectomy. In the normal subjects at rest, the upper lung fields showed no significant difference in the uptake rates of the two gases. In the middle and lower lung fields, however, the uptake rate for Xe-133 was higher than for N-13. During exercise a significant increase of the specific ventilation was found in the upper lung fields for N-13 compared with Xe-133. In the pneumonectomy patients the overall uptake rate for Xe-133 in the intact hemithorax was 25% larger than for N-13. Over the pneumonectomized hemithorax the uptake of the fastest component of Xe-133 was (8.5 +/- 1.3)% of the total. The total chest-wall contribution of Xe-133 was (27 +/- 8)% of the total count rate.

Rapid decarboxylation of carbon-11 labelled DL-DOPA in the brain: a potential approach for external detection of nervous structures.

The cerebral distribution of the positron-emitting agent [1-11C]beta-(3,4-dihydroxyphenyl)-D,L-alpha-alanine ([11C]DOPA) was studied after intravenous injection in rats pretreated with the peripheral decarboxylase inhibitor, carbidopa. Within 15 min of injection the accumulation of carbon-11 was almost twice as high in cortical areas and cerebellum as in the striatum and the brain stem. After destruction of catecholamine-containing nerve endings with 6-hydroxydopamine, the level of carbon-11 in the striatum was higher than in rats not treated with this neurotoxin. Pretreatment of rats with haloperidol or L-DOPA did not change the distribution pattern of carbon-11. Without pretreatment with carbidopa a uniform distribution of the label in the brain was observed. We suggest that [11C]DOPA is a potentially useful agent for external detection with positron imaging systems in patients and large animals of brain regions rich in the enzyme dopa-decarboxylase. (EC 4.1.1.26).

A new cocktail for liquid scintillation counting of aqueous radioimmunoassay-samples.

The aim of this investigation was to find a scintillation mixture for counting up to 1 ml of plasma. We succeeded in obtaining a mixture of xylene/Triton X-100/mono- and di-butylphosphate, and called it Plasmasol. The properties were ideal for radioimmunoassays of steroids. Good dissolving properties, high counting efficiency, absence of chemiluminescence and a good stability and reproducibility with respect to the disintegrations per minute were achieved. The cost was only 25% of the commercially available ready-to-use liquid scintillation mixtures, with which a comparison was made.

Special problems in the radioimmunoassay of plasma aldosterone without prior extraction and purification.

A new method for the radioimmunoassay of plasma aldosterone is described. The assay is performed directly on plasma without extracting or purifying the aldosterone. The method fulfilled the usual requirements for the demonstration of accuracy. Extensive data on the properties of the antisera are given.

Estimation of plasma testosterone without extraction and chromatography.

A new radioimmunoassay for plasma testosterone in human blood plasma is described. The assay is performed directly upon the plasma without extraction and purification of the testosterone. Antibodies to testosterone-7alpha-carboxyethyl thioether-bovine serum albumin are used and data concerning the specificity of these antibodies are given.

Labelling of bleomycin with cobalt-57, indium-111, technetium-99m, mercury-197, lead-203, and copper-67.

The radiochemical purity of the cobalt-57 complex of bleomycin could be enhanced by adjusting the pH of the final product to a value between 5 and 6. This radiopharmaceutical appeared to have better tumor visualizing properties compared to the not neutralized preparation. The clinical use of the cobalt-57 bleomycin complex is however limited by the long physical half-life of the label, causing a risk of radioactive contamination. It appeared to be possible to label bleomycin with radioactive cations (111In3+, 99mTc4+, 197Hg2+ and 67Cu2+) having suitable gamma ray energies and short half-lifes. These bleomycin complexes showed a high radio-chemical purity judged by their behaviour on thin layer chromatography, paper chromatography, and electrophoresis, but their application as tumor visualizing radiopharmaceutical turned out to be disappointing compared with cobalt-57 bleomycin.

Clinical evaluation of radio-labelled bleomycin for tumor detection.

Investigations with bleomycin labelled with radionuclides other than 57Co in patients with cancer and in tumor-bearing animals are described. In patients 57Co-bleo appears to be a better tumor-seeking radiopharmaceutical than 111In-bleo, 99mTc-bleo or 197Hg-bleo. This can be explained by a higher stability in vivo and a better tumor-seeking property of 57Co-bleo and less disturbing activity in the cardiac pool and in bone and other normal tissues when assessing the scintigram. Results with 111In-bleo labelled in acidic solution are not essentially different from those with 111In-bleo labelled in neutral solution. Results of 197Hg-bleo are almost identical with those of 197HgCl2 regarding the tumor-seeking effect as well as the distribution in normal tissues and organs. Probably the complex of 197Hg to bleomycin is not stable in vivo. The superiority of 57Co-bleo over 99mTc-bleo, 197Hg-bleo and also over 67Cu-bleo is confirmed by experiments on tumor bearing animals. We may conclude that the indication for use of bleomycin as a tumor-seeking pharmaceutical labelled with 111In, 99mTc, 197Hg or 67Cu seems to be very limited.