Scandium(III) complexes of monophosphorus acid DOTA analogues: a thermodynamic and radiolabelling study with (44)Sc from cyclotron and from a (44)Ti/(44)Sc generator.

The complexation ability of DOTA analogs bearing one methylenephosphonic (DO3AP) or methylenephosphinic (DO3AP(PrA) and DO3AP(ABn)) acid pendant arm toward scandium was evaluated. Stability constants of their scandium(iii) complexes were determined by potentiometry combined with (45)Sc NMR spectroscopy. The stability constants of the monophosphinate analogues are somewhat lower than that of the Sc-DOTA complex. The phosphorus acid moiety interacts with trivalent scandium even in very acidic solutions forming out-of-cage complexes; the strong affinity of the phosphonate group to Sc(iii) precludes stability constant determination of the Sc-DO3AP complex. These results were compared with those obtained by the free-ion selective radiotracer extraction (FISRE) method which is suitable for trace concentrations. FISRE underestimated the stability constants but their relative order was preserved. Nonetheless, as this method is experimentally simple, it is suitable for a quick relative comparison of stability constant values under trace concentrations. Radiolabelling of the ligands with (44)Sc was performed using the radioisotope from two sources, a (44)Ti/(44)Sc generator and (44m)Sc/(44)Sc from a cyclotron. The best radiolabelling conditions for the ligands were pH = 4, 70 °C and 20 min which were, however, not superior to those of the parent DOTA. Nonetheless, in vitro behaviour of the Sc(iii) complexes in the presence of hydroxyapatite and rat serum showed sufficient stability of (44)Sc complexes of these ligands for in vivo applications. PET images and ex vivo biodistribution of the (44)Sc-DO3AP complex performed on healthy Wistar male rats showed no specific bone uptake and rapid clearance through urine.

Antiatherogenic effect of simvastatin is not due to decrease of LDL cholesterol in ovariectomized golden Syrian hamster.

The changes of the composition of blood lipoproteins caused by menopause could also change the effect of hypolipidemic therapy. Using an experimental model we studied the changes of serum lipids and the effect of immediate or delayed treatment with simvastatin on atherosclerosis after surgical menopause. Female golden Syrian hamster aged 6 months were fed hypercholesterolemic diet during the whole study. Atherosclerotic changes in thoracic and abdominal aortas were assessed by stereomicroscopic method after 12 weeks. Four experimental groups were studied: sham-operated animals (n = 5), ovariectomized animals (n = 9), ovariectomized animals treated for 12 weeks (n = 10), and ovariectomized animals treated 4 weeks after ovariectomy for 8 weeks (n = 9). The dose of simvastatin was 10 mg/kg of body weight. After 12 weeks, ovariectomized animals had tenfold higher concentration of triglycerides in LDL fraction and significantly higher prevalence of atherosclerosis than animals without ovariectomy. Treatment with simvastatin substantially decreased the prevalence of atherosclerotic changes, but otherwise did not change individual serum lipids including LDL cholesterol. However, it improved proportions of pro- and antiatherogenic serum lipids mainly by the increase of HDL cholesterol. The timing of simvastatin treatment had no significant effect on atherosclerotic changes or lipid parameters. Simvastatin treatment partly prevented atherosclerotic changes induced by ovariectomy. This effect was not mediated by decrease of LDL cholesterol, but by increase in HDL cholesterol.

[Experimental ischemic renal injury--effect of surgical technique and the protective effect of a nonpeptide angiotensin II antagonist (losartan)]. / Ischemické poskození ledvin v experimentu--vliv chirurgické techniky a protektivní úcinek nepeptidového antagonisty angiotenzinu II (losartanu).

Experimental renal ischaemic injuries are typically produced by temporary closure of the renal artery. In rats, two different methods of such temporary closure of the renal artery were compared: snaring of the artery by tourniquet, and clamping by a microsurgical bulldog clamp. The consequences of ischaemic periods 60, 90 and 120 minutes were evaluated. In different experimental series, the potential protective effect of non-peptic AT1 angiotensin II receptor antagonist losartan on postischaemic renal injury was evaluated. The seven-day survival and the degree of functional renal damage (according to the plasma levels of creatinine and urea) were analyzed 24 hours and 7 days after experimental renal ischaemia. Ischaemia, produced by the tourniquet led to a more significant renal damage than ischaemia caused by clamping of the renal artery by a microclamp (higher 7-day mortality rate, higher postischaemic plasma levels of creatinine and urea). Losartan decreased the consequences of renal ischaemia caused by the tourniquet, but did not change the outcome of renal ischaemia produced by microsurgical bulldog clamps. We found, that not only the duration of ischaemia and pharmacology, but even the surgical technique of producing renal ischaemia are important factors in experimental studies evaluating ischaemic renal damage. These findings provide evidence of the role of angiotensin II in postischaemic renal injury by a renal tourniquet. This particular mechanism is probably not involved, when renal artery is gently temporarily closed by a bulldog microclamp.

A transient role of the kidney in the maintenance of hypertension.

Using the Prague hypertensive rat (PHR), a model derived from the Wistar rat, in which a normotensive parallel, the Prague normotensive rat (PNR), was bred from the same parent pair (so that transplantation of organs between both these parallel rat model lines results in no distinct signs of rejection), we were able to show that hypertension travels with the kidney. Transplantation of a kidney from PHR to a bilaterally nephrectomized (BNX) PNR led to an increase in systolic blood pressure (SBP) in the recipient for 10 weeks after grafting. Similarly, a decrease in SBP was seen in BNX PHR for the same period of time after grafting a kidney from PNR. If, however, the SBP was measured over a longer period of time, because the elevated SBP slowly drops after grafting a kidney from PHR to BNX PNR, it is less than 130 mm Hg in the fourth month and thereafter. If BNX PHR receives a kidney from PNR, the decrease in SBP is permanent, amounting to 126.3 +/- 12.7 mm Hg one year after transplantation. The grafting of a heart from PHR to the abdominal aorta of PNR does not influence SBP. In conclusion, the presence of a kidney from PHR is necessary for the development, but is not sufficient for the maintenance of hypertension. The heart of PHR is not "hypertensogenic" as is the kidney.

The role of the kidney in the development of hypertension: a transplantation study in the Prague hypertensive rat.

It has been shown that genetic hypertension in rats usually "travels with the kidney". To elucidate the mechanism of this phenomenon further, experiments were carried out in the Prague hypertensive (PH) rat, a model of genetic hypertension derived from the Wistar strain, in which a normotensive parallel, the Prague normotensive (PN) rat, was also bred from the same parent pair. Thus, it is possible to transfer organs between both parallels without substantial signs of rejection and without the use of immunosuppressive drugs. Unilateral nephrectomy and transplantation of one kidney between PH and PN rats, did not affect the arterial blood pressure (BP). Transplantation of one kidney from PN rats to bilaterally nephrectomised PH rats normalised the high BP. If a PH rat was left with one original kidney in situ after the transplantation of a "normotensive" kidney, the high BP persisted until the original "hypertensive" kidney was removed. This removal resulted in sustained normalisation of BP. When the development of high BP in the PH rats was prevented for 2 months after weaning by antihypertensive drugs, transplantation of kidneys from these rats to bilaterally nephrectomised PN rats always induced a sustained hypertension in the recipient. These results argue against a role of high-BP-induced damage to the kidney and against an intrinsic increase in the salt-reabsorptive capacity of the tubular epithelium in PH rats. The data support the view that the kidney from PH rats produces a "hypertensinogenic" substance, the secretion of which is genetically determined and is not influenced by the magnitude of the BP.

Heart protection by cardioplegic solutions containing oxyhemoglobin pretreated by carbontetrachloride and freeze-drying with sucrose.

A technologically improved variant of native stroma-free oxyhemoglobin (SFH) pretreated by carbontetrachloride and freeze-drying with 240 mM sucrose were reconstituted in a properly diluted ionic solution to reach the final concentration of 66 g oxyhemoglobin/L, osmolality 280-320 m0sm and pH 7.4. Cardioplegia of isolated rat heart was induced and maintained by this solution without recirculation for 3 h at 20 degrees C prior to heterotopic allo-transplantation of the graft. Evaluation of the survival and performance of each graft after 24 h and extent of tissue necroses indicated that the given standardly produced SFH variant ensured reproducible heart preservation from ischemic and reperfusion injury similarly as did the renown crystalloid cardioplegic solution CUSTODIOL.

Hemoglobin solutions in experimental cardioplegia.

The addition of stroma-free hemoglobin solution to a standard St. Thomas Hospital cardioplegic solution significantly protected the heart from ischemic damage compared to the effect of the same solution without added hemoglobin. An experimental model of rat heart cardioplegia and transplantation comprising heart arrest for three hours at 20 degrees C was used. The number of hearts performing strong contractions after cardioplegia with iso-oncotic oxyhemoglobin prior to transplantation was close to the results with histidine-buffered cardioplegic solution according to Bretschneider. Comparative biochemical model experiments in vitro confirmed that the positive effect of oxyhemoglobin was due predominantly to its buffering capacity. The role of oxygen transport to tissues by hemoglobin was limited only to the first minutes of cardioplegia since neither recirculation nor reoxygenation took place in the present experimental setting.

[Immunosuppressive therapy with low cyclosporin A doses in rats]. / Immunsuppressive Therapie mit niedrigen Cyclosporin-A-Dosen bei Ratten.

An optimum blood level of cyclosporine-A (Cs-A) after allotransplantation in rats is very important for the survival of the transplanted organ. An auxiliary allotransplantation of the heart into the abdominal cavity were carried out in 10 rats. A Cs-A blood level of 200 to 300 ng ml was obtained by administration in the animal food in a dosage of 7 mg kg body weight day. A rejection of the graft was prevented in this way without any symptom of toxicity during 90 days. The results of the experiments were well reproducible. The obtained Cs-A blood level is relatively stationary, frequent laboratory tests are not necessary.