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Biomedical subjects

A Hoekstra

Publications and source records attributed to A Hoekstra.

At least 37 records · Page 2Linked to original sources
PubMed1994

Pain relief mediated by implantable drug delivery devices.

Various totally implantable drug delivery systems from single access ports to micropumps are now available for administration of repeated boluses, and continuous or programmable infusions. In this respect, emphasis is given to a relatively cheap, totally implantable system for self-administering intraspinal opiates in the treatment of cancer pain. The SECOR pump system, developed by Cordis, consists of a dual pump with refill port and safety valve. The volume of the pliable reservoir is 12 ml and refill is accomplished with a 25-G needle. The bolus delivered with each transcutaneous activation of the pumps is 0.1 ml. Clinical results demonstrated that this patient-controlled drug delivery system is safe and provides excellent pain relief associated with terminal cancer. A possible advantage of this drug delivery system over continuous infusion pumps is that patients can elect to have the morphine delivered only when they feel pain. Thus pain relief would be maximized and tolerance build-up would be minimized.

Analgesia, Epidural↗
PubMed1993

Clinical evaluation of the CORDIS vascular access port systems: a multicenter study.

Two non-metallic vascular access port systems, the Multipurpose Access Port (MPAP) and Miniport, developed by CORDIS S.A., France, have been evaluated clinically in 78 cancer patients. During the investigational period covering a total experience of 369 treatment cycles and 1,370 infusion days, no cases of infection or septicemia were observed. Serious complications such as drug extravasation and catheter occlusion occurred, although the incidence was relatively low (+/- 1%) when compared with the number of treatment courses (cycles), but in relation to the number of patients included in this study, the procedure-related complication rate was 17.5% for the MPAP and 15.8% for the Miniport. Procedure-related complications can be avoided by proper handling and use of suitable drug combinations to minimize crystallization reactions within the port-catheter systems. The final complication rate (total minus procedure-related) in terms of termination of treatment, i.e. explantation of the port-catheter system was 12.1% for the MPAP and 12.5% for the MINIPORT, which generally confirms the results of other groups. More than 87% of both port-catheter systems were still functional at the end of evaluation.

Adult↗
PubMed1991

Bone growth and remodeling after distraction epiphysiolysis of the proximal tibia of the rabbit. Effect of electromagnetic stimulation.

The effect of pulsed electromagnetic stimulation on bone formation was tested in a lower-limb-lengthening model in the rabbit. Limb lengthening was performed by distraction epiphysiolysis. A specially designed external distraction device allowed 10 mm of lengthening of the tibia. Coils to generate a pulsed electromagnetic field were clipped onto the distractor. Stimulation started after a distraction period of three weeks and was continuous for 18 weeks. A control group received the same treatment without stimulation. Bone formation in the elongated zone was evaluated by computed tomography, scintigraphy, and histology. Bone healing involved accretion of callus followed by a process of remodeling, resulting in the formation of a solid cortex. The formation of a diaphysislike structure at the original site of the metaphysis progressed from the distal end of the elongated zone upward. Electromagnetic stimulation had no effect on the rate or extent of bone formation and remodeling.

Animals↗
PubMed1990

Effect of direct current stimulation on bone growth after distraction epiphysiolysis of the rabbit tibia.

The effect of direct current stimulation on bone formation during limb lengthening was tested in a lower leg lengthening model in the rabbit. Limb lengthening was performed by distraction epiphysiolysis. A specially designed external distraction device was placed at the tibia. The distractor allowed 10 mm of lengthening in 4 weeks. Two weeks after starting the distraction, a platinum electrode was passed through the anterior cortex below the tibial tuberosity and advanced via the medullary cavity so that the tip rested in the elongated zone. Stimulation started at the time of placement of the electrodes and was continued for 3 weeks. The electrode in the elongated zone served as the cathode; the anode was placed subcutaneously. A 20 microA stimulus was selected. A control group received the same treatment without stimulation. Bone formation in the elongated zone was evaluated by histology and scintigraphy. The data from this experiment show that direct current stimulation in the early phase of a limb lengthening procedure had no effect on the extent of bone formation in the elongated zone.

Animals↗
PubMed1990

The value of local 99mTc(Sn)-MDP bone to soft tissue uptake ratio in osteoporosis, before and during fluoride therapy.

The reproducibility and diagnostic value of local bone to soft tissue uptake ratio of 99mTc(Sn)-MDP as a bone tracer was examined in a prospective study in 35 patients who were under investigation and/or treatment for postmenopausal osteoporosis. The ratio of tracer uptake in the second lumbar vertebra (L2) and both femoral shafts was calculated from the number of counts in suitable regions of interest. Results obtained with settings and calculations in the routine practice were compared to the results obtained by revision of all raw data in one run by one person. The results were compared to the serum alkaline phosphatase activity (AP) and to local bone mineral mass as determined by dual photon absorptiometry (DPA). In 15 patients serial measurements during fluoride therapy were also compared to serum osteocalcin values and to bone histomorphometric data. The precision error of the calculation of uptake ratios from raw counts (including selection of region of interest) was 13.9% for the femoral shaft and 14.7% for L2. The mean difference between left and right femoral shaft in individuals was not significant and its variance was small P greater than 0.1). There was a weak but significant linear correlation between local uptake ratio in the spine and AP in the total material (r = 0.328 P less than 0.01). However, changes in local uptake ratio during therapy with fluoride in 15 patients were too small to be of any value and did not correlate with changes in alkaline phosphatase or osteocalcin or trabecular surface covered with osteoblasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Effect of ICS 205-930 (a specific 5-HT3 receptor antagonist) on gastric emptying of a solid meal in normal subjects.

The effects on gastric emptying of a solid meal of the specific 5-HT3-receptor antagonist ICS 205-930, 10 mg and 20 mg intravenously were assessed with a scintigraphic technique in 12 normals. The 50% emptying time was less, the lag phase was shorter and the post lag emptying rate was faster after 20 mg ICS 205-930 (p less than 0.02). After 10 mg ICS 205-930 the lag phase was significantly shorter compared with placebo (p less than 0.04). These results suggest that 5-HT3 receptors may be involved in the regulation of gastric emptying in man.

Adult↗
PubMed1988

Bone healing during lower limb lengthening by distraction epiphysiolysis.

A study of limb lengthening by distraction epiphysiolysis in the rabbit tibia is presented. A special external distraction device was developed that allowed 10 mm lengthening of the leg. Bone formation in the elongated zone was studied by computed tomography and [99mTc] methylene diphosphonate (MDP) scintigraphy. Computed tomography showed bone formation proceeding for several weeks after the end of the distraction period, followed by a decrease in the amount of bone during a remodeling phase leading to the formation of a solid cortical structure. The uptake of [99mTc]MDP increased parallel to, but preceeding the actual accretion of bone, followed by a decrease during the bone remodeling phase. Uptake of the tracer will partly reflect bone metabolism, but other factors, like trauma, determine much of the uptake.

Animals↗
PubMed1987

Monitoring fluoride therapy in osteoporosis by dual photon absorptiometry.

Dual photon absorptiometry (DPA) was used to evaluate changes in bone mineral mass in 108 osteopenic patients. Ninety were treated with fluoride and 18 served as controls. All osteopenic patients and 9 of the controls took calcium and vitamin D supplements. In 16 women estrogens were combined with the fluoride therapy. Seven patients received prednisone. Significant positive changes in bone mineral mass in the lumbar spine could be demonstrated over a mean observation time of 14-15 months in all groups treated with fluoride but not in the control group. The average increase in bone mineral mass in the lumbar spine (L2, L3 and L4 combined) ranged from 3.57% +/- 1.42% (sem, p less than 0.05) in women on fluoride to 10.36% +/- 3.17% (p less than 0.01) in men and 10.18% +/- 2.39% (p less than 0.001) in women on estrogen and fluoride. Changes in bone mineral mass in femoral necks (left and right combined) and femoral diaphysis were not significant. In the control group no significant changes were observed (lumbar spine: -1.68% +/- 1.75%, femoral necks -0.09% +/- 3.3% and femoral diaphysis -2.32% +/- 2.40%). It is concluded that a positive effect of fluoride on trabecular bone in the spine can be demonstrated with DPA on a group basis when data processing is done in a uniform way by a single observer. Its longitudinal use in individual patients necessitates a series of measurements to overcome the analytical error.

Adult↗
PubMed1987

Radioiodinated Rhodamine-123: a potential cationic hepatobiliary imaging agent.

The labelling of the cationic dye Rhodamine-123 with 125I is described. The biodistribution of the iodinated Rhodamine-123 has been determined at different time intervals after intravenous injection into fasted rats. It turned out that the dye is predominantly cleared by the liver and discharged into the bile. The bile acid taurocholate did not enhance the rate of excretion of 125I-Rhodamine-123.

Animals↗
PubMed1986

Evaluation of the renal scanning agent N-succinyldesferrioxamine B in dogs.

The mechanism of the excretion of 67 Ga-N-succinyldesferrioxamine B (SDF) was investigated in five healthy dogs. Comparison of the SDF clearance rates for whole blood and plasma as well as SDF renograms with those of 131 I-o-iodohippuric acid (OIH) and 111In-diethylenetriamine-pentaacetic acid (DTPA) revealed that SDF is cleared by glomerular filtration and not by an active tubular transport mechanism.

Animals↗
PubMed1986

Synthesis and tumour-localizing properties of [18F]-5-fluorocytosine-arabinoside and [18F]-5-fluorocyclocytidine.

[18F]-5-fluorocytosine-arabinoside (2) and [18F]-5-fluorocyclocytidine (4) were prepared by reaction of [18F]-acetylhypofluorite with cytosine-arabinoside (1) or cyclocytidine (3) in acetic acid and were isolated in an overall radiochemical yield of 20% and 9%, respectively. The biodistribution of both radiopharmaceuticals was determined in melanoma bearing Syrian golden hamsters. It was found that 2 is a good tumour-localizing agent for pigmented and non-pigmented Greene melanoma.

Ancitabine↗
PubMed1986

On the mechanism of gallium accumulation in tumours. Isolation of N-hydroxypeptides.

With the use of A SEP-PAK Alumina N cartridge, peptide fractions containing the hydroxamate moiety have been isolated from tumour-tissue homogenate. It is therefore postulated that N-hydroxypeptides might play a role in the accumulation of gallium-67 in tumours. The biodistribution of several 67Ga-labelled hydroxamate peptide fractions is determined. Although their biodistribution differs from that of 67Ga-citrate no enhancement in tumour accumulation is observed indicating that they do not act like tumour-specific siderophores.

Animals↗
PubMed1985

The placenta as a substitute for cancerous models.

The tissue distribution of various radiopharmaceuticals was investigated in Rhabdomyosarcoma-bearing rats and in pregnant rats during the period of rapid foetal and placental growth (days 17-19 of pregnancy). The results indicate that with the radiopharmaceuticals tested the uptake in placental tissue followed closely the data obtained with tumour tissue in Rhabdomyosarcoma-bearing rats (1). We describe here the parallels between cell replication in the placenta and in malignant tumours and propose that the placenta merits more attention in the field of biomedical research.

Animals↗
PubMed1985

Synthesis and biodistribution of [18F]-5-fluorocytosine.

[18F]-5-fluorocytosine was prepared by reaction of [18F]-acetylhypofluorite with cytosine in acetic acid and was isolated in an overall radiochemical yield of 20%. Tissue distribution studies in sarcoma-bearing rats indicated in vivo stability, limited tissue uptake and rapid urinary excretion.

Animals↗
PubMed1984

N-Succinyldesferrioxamine B: a potential radiopharmaceutical for assessing renal function.

N-Succinyldesferrioxamine B was found to be cleared very fast by the kidneys. Since this compound can strongly chelate several metals, including the generator-produced isotopes 113mIn and 68Ga, 67Ga-N-succinyldesferrioxamine B (SDF) was tested as a substitute for 131I-o-iodohippuric acid (OIH) in the measurement of renal tubular secretion. In rats both compounds showed similar biodistribution patterns with a greater excretion rate of SDF. In rabbits, however, the excretion rate of OIH was superior to that of SDF. Inhibition of tubular secretion by probenecid was nearly ineffective in the renal clearance of both OIH and SDF.

Animals↗
PubMed1984

The effects of chlorpromazine, mianserin and Org GC94 on reproductive function in the rat.

In the assessment of drug safety with respect to mammalian reproductive function chlorpromazine and two serotonin antagonists, mianserin (Org GB94 ) and Org GC94 were studied for their effects on ovulation and ovum transport. In addition, the effect of coitus on drug-induced ovulation inhibition was investigated. The compounds were intragastrically administered to Charles River CD rats in a single dose or in consecutive daily doses for one or two weeks. The incidence of ovulation and the number of eggs were recorded. The compounds blocked ovulation in pro-oestrous rats after a single dose. Ovulation was restored by coitus in drug-treated animals. The compounds appeared to become less effective in blocking ovulation after multiple dosing. No effects on ovum transport were detected. From the results obtained in this study, it is concluded that the CNS-active drugs investigated did not adversely affect reproductive function in the rat.

Animals↗
PubMed1984

The developing placenta in selecting potential radiopharmaceuticals for tumour-localizing properties: a simple in vivo pre-screening model.

The tissue distribution of various radiopharmaceuticals was investigated in rhabdomyosarcoma-bearing and in pregnant rats during the period of rapid foetal and placental growth (days 17-19 of pregnancy). The preliminary results indicate that with the radiopharmaceuticals tested the uptake in placental tissue followed closely the data obtained with tumour tissue in rhabdomyosarcoma-bearing rats.

Animals↗