Skeletal muscle glucolysis, glycogenolysis and glycogen phosphorylase during electrical stimulation in man

Phosphorylase activity, glycogenolytic and glucolytic rates were estimated in human quadriceps muscle during electrical stimulation at 20 Hz. Two stimulation periods of 10 s duration were separated by a pause of 60 s. The blood circulation to the leg was intact or occluded during the experiment. ATP turnover rates and force production were of the same order during the two contraction periods both with and without intact blood flow. Also the increase in phosphorylase a activity (from approximately 30% to approximately 65%) was the same during the contraction periods. Glycogenolytic and glucolytic rates were however about 30% higher (P less than 0.05) during the second contraction compared with the first when circulation was occluded, but similar when the circulation was intact. During the 60 s rest period, the phosphocreatine (PCr) was maintained at a low level and inorganic phosphate (Pi) remained increased under occluded circulation while PCr was resynthesized in the rest period with intact circulation. We conclude that the increased glycogenolytic rate observed during the second contraction with occluded blood circulation was due to the high [Pi] in the muscle and that the increased glucolytic rate was caused by high [Pi] and low [PCr]. In the rest period with anoxia the glycogenolysis was completely inhibited and glucolysis was inhibited by 95% in spite of the changes in [PCr] and [Pi].

In vivo and in vitro receptor autoradiography of the human brain using an 11C-labelled benzodiazepine analogue

In vitro autoradiography of an 11C-labelled ligand, Ro 15-1788, has been used to visualize benzodiazepine binding sites in large human brain cryo-sections. In parallel, using the same radioligand, an in vivo study of a human healthy volunteer was performed, by means of positron emission tomography (PET). The in vitro and in vivo mapping of the ligand demonstrated a very similar binding pattern, although the poor resolution of PET precluded a full discrimination of fine details. The 11C-autoradiograms showed good spatial resolution, even with distinction of different layers in the cerebral and cerebellar cortex. In a separate experiment, the spatial resolution of 11C-autoradiography was found to be 180 microns, using 80-microns-thick cryo-sections. It is emphasized that in vitro and in vivo studies of the same radioligand give complementary information, which is valuable in the assessment of PET images.

Malignant prolactinoma with multiple intracranial metastases studied with positron emission tomography

A rare case of a patient with multiple intracranial metastases from a prolactin-secreting pituitary neoplasm is described. At the age of 14 years, the patient had been operated on for a sellar tumor; he presented 12 years later with severe headache, at which time computed tomographic and magnetic resonance imaging scans revealed multiple intracranial metastases. Histopathology examination showed pituitary neoplastic cells with positive immunostaining for prolactin. The patient was investigated with positron emission tomography (PET) and dopamine D2-receptor binding, and the amino acid metabolism of the tumor was characterized in vivo. High dopamine D2-receptor binding and high amino acid metabolism were found in the tumor. The patient was subsequently treated with bromocriptine injections that resulted in a decrease in serum prolactin levels, decreased dopamine D2-receptor binding, reduced amino acid metabolism, and a reduction in tumor volume. This case demonstrates a beneficial effect of bromocriptine treatment in a patient with prolactinoma with multiple intracranial metastases. It also illustrates the great potential of PET in the in vivo characterization of the D2-binding and the high sensitivity of 11C-labeled L-methionine in the follow-up of treatment in patients with pituitary adenomas.

Positron emission tomography with 11C-methionine and computed tomography of intracranial tumours compared with histopathologic examination of multiple biopsies

A selected group of 36 patients with suspected supratentorial gliomas were investigated with positron emission tomography (PET) using 11C-methionine and transmission computed tomography (CT) before and after intravenous injection of contrast medium. Every examination was performed with the head fixed in a plastic helmet and a baseplate to guarantee that the slice orientation was the same at examinations with the two modalities and over time. Guided by the examinations, multiple stereotactic biopsies were performed with the biopsy instrument mounted on the baseplate. Regional accumulation of methionine was compared with histology of the corresponding samples and with attenuation before and after injection of contrast medium as well as mass effect on CT. Typically, there was a low attenuating lesion with a slight mass effect on CT. There was an increased accumulation compared with normal brain tissue in 31 cases of tumours and ordinary or decreased accumulation in 3 cases of tumours. In 22 cases with increased accumulation of methionine the extension of the tumour judged by PET corresponded with that of histology. In 4 cases tumour cells were found outside the area with pathologic methionine uptake. In 5 patients there were areas with increased methionine accumulation where no tumour cells were found. In 22 cases PET using methionine was more accurate than CT in defining the tumour boundaries as determined from the histologic findings. Four groups of biopsy specimens with different amounts of methionine accumulation are described. The uptake in a single biopsy gives good but not exact information about the histology of the specimen.

An adaptor to the Leksell stereotaxic instrument for digital coordinate determination in radiography

Special perspex adaptors with radiopaque reference structures have been constructed to fit to the Leksell stereotaxic instrument. These structures are visualized on X-ray film in a radiographic examination like angiography or encephalography. The films obtained in two projections at arbitrary angles and focus-film-distances are placed on a digitizing table for the determination of the stereotaxic coordinates of selected targets. The reference structures and the targets are marked with a cursor whereupon a desk top computer performs the calculation of the stereotaxic coordinates. The system allows a rapid, simple and accurate coordinate determination in stereotaxic radiography using the Leksell stereotaxic instrument.

Rapid decrease in amino acid metabolism in prolactin-secreting pituitary adenomas after bromocriptine treatment: a PET study

Four patients with prolactin-secreting pituitary adenomas were examined with positron emission tomography using L-[11C]methionine to monitor the effect of dopamine agonist treatment on the amino acid metabolism in the tumors. Within the first few hours after intramuscular injection of bromocriptine retard (50 mg) the amino acid metabolism decreased by 40%. Two of the patients were reexamined 7 and 9 days later and showed a 70% reduction in the metabolism of the adenomas. This metabolic effect was later accompanied by significant tumor shrinkage in all adenomas. It is suggested that bromocriptine has a general and rapid effect on the protein synthesis of the prolactin-secreting pituitary adenoma cells.

Application of a kinetic model on the methionine accumulation in intracranial tumours studied with positron emission tomography

Eleven patients were studied with positron emission tomography (PET) using 11C-methionine. They all had low-grade astrocytomas (Kernohan grade II). The PET studies were analyzed with a metabolic model to obtain values for the influx, the accumulation rate and the partition coefficient of methionine in normal and tumourous tissue. Seven of the tumours showed an increased accumulation of methionine as compared with normal tissue on the static PET scans and also had higher values as to the kinetic parameters. Four tumours had a methionine accumulation equal to or lower than that of normal tissue and the kinetic parameters were also lower. Application of the kinetic model did not aid significantly in the delineation of the tumours. There was a correlation between the three parameters indicating an adaptation of the transport of methionine to the regional metabolic demand. The accumulation rate for normal cortical tissue was 0.49 nmol/g/min, the influx 0.97 nmol/ml and the partition coefficient 0.45 ml/g. These values are considerably higher than those previously reported. The differences might be attributed to differences in the corrections introduced for i.a. the occurrence of labelled metabolites in serum. With the use of a kinetic model, more information about the tracer is utilized and gained compared with the previously used graphic approach.

ATP utilization and force during intermittent and continuous muscle contractions

Energy utilization and force generation under anaerobic conditions were studied in electrically stimulated quadriceps femoris muscle of four volunteers. To investigate the effects of intermittent vs. continuous stimulation one leg was stimulated intermittently and the other continuously during 50 s. The same initial force was produced, and biopsy samples were obtained before the stimulation and after 10, 20, and 50 s and analyzed for energy-rich phosphagens, glycolytic intermediates, and phosphorylase. The ATP utilization and glycolysis were greater during intermittent contraction, but glycogenolysis was equal. ATP content decreased to lower values after intermittent contraction (16.4 compared with 19.6 mmol/kg dry muscle after continuous contraction). Force generation was well preserved during continuous contraction but successively decreased after 20 s of intermittent stimulation down to 50% of initial at end of work. The energy cost per unit work was greater during intermittent stimulation and increased with contraction time, whereas it decreased with time during continuous stimulation. The decrease in force generation in intermittent exercise is suggested to be due to the higher energy cost for contraction resulting in greater changes in the intracellular environment with lower ATP and increased H+ and Pi. These changes would decrease both activation of the contractile system and the cross-bridge turnover rate resulting from activation.

Comparison of the accumulation kinetics of L-(methyl-11C)-methionine and D-(methyl-11C)-methionine in brain tumors studied with positron emission tomography

Five patients with glioma were examined with positron emission tomography after the administration of 11C-L-methionine and at a following day with 11C-D-methionine. The rates of accumulation of the tracers were determined in the tumor and in the normal brain tissue according to a graphical technique of Patlak et coll. The accumulation rates for L-methionine were on the average 2.4 times higher than those of D-methionine in the tumors. The corresponding ration for normal brain tissue was 2.3. It is concluded that in this group of tumors without obvious blood-tumor-barrier breakdown, a stereospecific process with similar properties as in the normal brain tissue, is responsible for the accumulation of the labelled methionine.

The normal pituitary examined with positron emission tomography and (methyl-11C)-L-methionine and (methyl-11C)-D-methionine

Four patients with radiologically normal pituitary gland were examined with positron emission tomography after the administration of (methyl-11C)-L-methionine. On a following day the examination was repeated with (methyl-11C)-D-methionine. The accumulation rate of L-methionine in the pituitary was measured, giving a value that was about twice that of normal brain tissue. The accumulation rate of D-methionine in the pituitary was almost a factor of 10 lower than that of L-methionine. In the normal brain tissue that ratio was 2.3. The study clearly indicates that the methionine uptake in the pituitary is stereospecific. 11C-D-methionine is freely distributed in the tissue without entrapment, whereas 11C-L-methionine is irreversibly bound. It is concluded that PET with 11C-L-methionine can be used to study amino acid utilization in the pituitary.

Amino acid distribution and metabolism in pituitary adenomas using positron emission tomography with D-[11C]methionine and L-[11C]methionine

Four patients with hormonally inactive pituitary adenomas were examined with positron emission tomography (PET) after injection, during different examinations, of L-[methyl-11C]methionine and D-[methyl-11C]methionine, respectively. After the rapid distribution phase, the enantiomer L-[11C]methionine, which is metabolically active, showed a considerable continuous irreversible trapping attributed to amino acid metabolism. The stereoisomer D-[11C]methionine, which does not participate in protein synthesis, showed a rapid distribution within the whole adenoma tissue, with a distribution space on the order of 100%. A minimal irreversible trapping was observed which could be explained by technical factors. It is concluded that PET using the two enantiomers allows a separation of passive distribution and metabolism, and that L-[11C]methionine can be used for in vivo quantitative studies of amino acid metabolism of pituitary adenomas.

PET study of methionine accumulation in glioma and normal brain tissue: competition with branched chain amino acids

Five patients with glioma were examined with positron emission tomography using ([11C]methyl)-L-methionine. The study was repeated while the patient was being infused with branched chain amino acids (BCAA), 250 mumol/min. The accumulation rates of methionine in tumor tissue and in normal brain tissue were compared without and with the infusion of amino acids. Both tumor tissue and normal brain tissue showed a reduction in the methionine accumulation by 35% while the patient received the infusion. In one patient with a severe blood-tissue barrier disruption the tumor accumulation rate was unaffected. It is concluded that in gliomas without severe blood-tissue barrier disruption, the accumulation of methionine is governed by processes exhibiting similar properties regarding competition with BCAA as in normal brain tissue.

Anaerobic energy release in skeletal muscle during electrical stimulation in men

The quadriceps femoris muscles of seven men were electrically stimulated under extended anaerobic conditions to quantitate anaerobic energy release and the contribution of the glycolytic system to total ATP production. Muscles were intermittently stimulated 64 times at 20 Hz while leg blood flow was occluded. Each contraction lasted 1.6 s and was followed by 1.6 s of rest. The total contraction time was 102.4 s. Muscle biopsies were taken at rest and following 16, 32, 48, and 64 contractions. The ATP turnover rates during the four 16-contraction periods were 6.12, 2.56, 2.17, and 0.64 mmol X kg dry muscle-1 X s-1 contraction time. Glycolysis provided 58%, phosphocreatine 40% and a decreased ATP store 2% of the consumed energy during the initial 16 contractions. Glycolysis was responsible for 90% of the total ATP production beyond contraction 16. Absolute glycolytic ATP production decreased to 60, 55, and 17% of the amount in the initial 16 contractions during the final three periods, respectively. In conclusion glycolysis produced approximately 195 mmol ATP/kg dry muscle during the initial 48 contractions (76.8 s) and only approximately 15 mmol ATP/kg dry muscle during the final 16 contractions. Equivalent values for total ATP turnover were 278 and 16.5 mmol/kg dry muscle.

Skeletal muscle glycogenolysis, glycolysis, and pH during electrical stimulation in men

Glycogenolytic and glycolytic rates were estimated and muscle pH (pHm) was measured in electrically stimulated quadriceps femoris muscles of seven men. Leg blood flow was occluded and muscles were stimulated 64 times at 20 Hz, with contractions lasting 1.6 s and separated by pauses of 1.6 s. Muscle biopsies were obtained at rest and following 16, 32, 48, and 64 contractions. Glycolytic intermediates and several modulators of the glycolytic enzyme phosphofructokinase (PFK) were measured. Glycogenolytic and glycolytic rates were 1.68 and 1.26 mmol glucosyl units X kg dry muscle-1 X S-1 contraction time during the initial 16 contractions and pHm decreased from 7.00 +/- 0.01 to 6.70 +/- 0.03. During the subsequent 32 contractions both glycogenolytic and glycolytic rates were maintained at approximately 0.70 mmol X kg-1 X S-1 and pHm decreased to 6.45 +/- 0.04. In the final 16 contractions, both rates were very low and pHm was unchanged. Therefore, PFK remained active despite increasing acidity until pHm decreased to approximately 6.45. We conclude that increases in the concentrations of several positive modulators partially reverses pH-dependent ATP inhibition of PFK in vivo, permitting glycolytic activity to continue in the pHm range of 6.70-6.45.

Transsphenoidal therapeutic puncture of a cystic pituitary adenoma

Transsphenoidal diagnostic puncture of skull base tumours has been a routine procedure in Uppsala for a decade. Bromocriptine is the treatment of choice for patients with prolactin secreting pituitary adenomas. Here we report on a patient with a pituitary adenoma who instead developed an increase in tumour size after bromocriptine treatment. Magnetic resonance imaging showed the tumor to be cystic. A transsphenoidal puncture was used therapeutically instead of surgery with excellent result.

11C-labelled glycine: synthesis and preliminary report on its use in the investigation of intracranial tumours using positron emission tomography

Carbon-11-labelled glycine has been prepared by a Bücherer-Strecker synthesis using [11C]cyanide, formaldehyde and ammonium carbonate. Total synthesis time, including chromatographic purification, was 30-35 min from end-of-bombardment. Radiochemical yield was 35%, based on [11C]cyanide and radiochemical purity was shown to be greater than 98% by analytical HPLC. The 11C-labelled glycine thus prepared was used along with [68Ga]EDTA and L-[methyl-11C]methionine in the visualization of an anaplastic astrocytoma by positron emission tomography.

Positron emission tomography of cavernous haemangiomas of the brain

Four cases with lesions suspected to be low-grade intracerebral tumours but later proved to be cavernous haemangiomas are described. The patients were examined with contrast enhanced CT and with positron emission tomography (PET). The lesions were partly calcified with a mild or no mass effect and a slight contrast enhancement at CT. There were signs of disrupture of the blood-lesion barrier also on radionuclide studies. PET with 11C-methionine and 11C-glucose showed a normal or decreased accumulation of the tracers. This combination of findings has not been encountered in intracranial tumours. As a comparison, one case of glioblastoma is described. In this patient, the CT findings suggested a cavernous haemangioma. However, PET showed a markedly increased accumulation of 11C-methionine, which is compatible with brain tumour but not with haemangioma.

Relaxation time during intermittent isometric contraction in subjects with different capacity for oxidative work

Force and relaxation time were measured during intermittent electrical stimulation of the quadriceps muscle on 14 volunteers. Each stimulation had a duration of 1.6 s and the work to rest ratio was 1:1. Relaxation times increased during the first 20-30 contractions and then reached a plateau. The rate of increase in relaxation time during the first contractions as well as the plateau levels were found to correlate to maximal oxygen uptake capacity, predicted from submaximal cycle ergometer tests. Since slow-twitch fibres are known to produce work at a lower energy cost it is suggested that studies of relaxation time changes could provide functional estimates of fibre-type proportions in the quadriceps muscle.

Scatter distribution in transmission measurements with positron emission tomography

The distribution of scattered radiation was measured for transmission scans in positron emission tomography by adding the scattered radiation distributions in different projections from line source experiments. It is shown that in a 20 cm diameter water-filled phantom the scattered radiation effects contribute approximately one-third of the events centrally in the field of view. This may lead to systematic errors of the order of 15-25% in reconstructed images. A scheme for correction for scattered radiation effects in the transmission scans is described and tested in phantom experiments.

Dopamine receptors in pituitary adenomas: PET visualization with 11C-N-methylspiperone

Two patients with pituitary tumors were examined with positron emission tomography (PET) after intravenous administration of 11C-N-methylspiperone. In repeat studies the patients were given 1 mg of intravenous haloperidol prior to the administration of the radioligand to block the dopamine receptors. High uptakes of the radiolabeled ligand were seen in one of the tumors. With haloperidol pretreatment the uptake was lower, probably mainly showing the remaining unspecific binding. The most marked uptake and the largest effect of haloperidol pretreatment was seen in a patient with a hormonally active prolactinoma. Dopamine receptor binding in pituitary tumors can be demonstrated in vivo with PET, and quantification of this binding is possible using a compartmental model. This technique may be useful in improving our understanding of the variable response to medical treatment of prolactinomas with dopamine agonists as well as in the prediction of the effect of such treatment.

A method of stereotaxic localization adopted for conventional and digital radiography

A method for the determination of stereotaxic coordinates in radiography, e.g. angiography, pneumoencephalography or digital vascular radiography, is described. A special localization frame containing radiopaque structures and scales defines a diagnostic coordinate system. This frame is fixed to the X-ray-table prior to the radiographic procedure and two projections are obtained at arbitrary angles to each other. The focus-film distances do not how to be fixed. The target coordinates are then determined either by a simple graphical procedure or with the use of a digitizing x-y-table, by a computer. With the computer method the films are placed on the digitizing table and the target and a few reference points are marked using a cursor. From the relative positions the computer calculates the coordinates. With the special head fixation system, coordinates of structures visualized in radiographic examinations can be transferred to various therapeutic or diagnostic stereotaxic devices.

Stereotactic radiation therapy of intracranial lesions. Methodologic aspects

A technique for stereotactic radiation therapy of cerebral tumours and arteriovenous malformations using a linear accelerator (6 MV photons) is proposed. Treatment relies on a fixation system that permits a precise use of the coordinates estimated at stereotactic angiography or stereotactic computed tomography. The field of treatment can be exactly outlined in the CT images during repeat examinations, thus facilitating the recognition of changes induced by radiation. The system also allows the extent of the arteriovenous malformation, as seen at angiography, to be accurately traced in the CT sections thus enabling evaluation of possible radiation damage to surrounding brain structures. The precision of the method as well as its hypothetical merits and disadvantages are discussed. The number of patients treated is still small and the follow-up time is too short in the majority of cases to allow definite conclusions. Examples of preliminary results are given.