Evaluation of cardiovascular effects of caffeine using telemetric monitoring in the conscious rat.

Caffeine (1,3,7 trimethylxanthine) affects the cardiovascular system, with potential toxic effects ranging from a moderate increase in heart rate to more severe cardiac arrhythmias. Telemetry transmitters were implanted in Wistar rats in the peritoneal cavity with a pressure catheter in the aorta and electrodes for electrocardiogram (ECG) recording subcutaneously. After a single oral administration of saline, each rat was administered single oral doses of 5, 15 and 45 mg/kg b.w. of caffeine. Caffeine was found to induce, to various degrees, a dose-dependent early increase in spontaneous physical activity, heart rate, dp/dt and systolic-diastolic blood pressure. No arrhythmias or visual changes were observed in the ECG complex. High doses induced more strong responses and of longer duration. The increase in systolic blood pressure at the median dose remained in the rats until 20 h after administration. However, the highest dose of caffeine (45 mg/kg b.w.) induced a biphasic response, with an early and pronounced increase in body temperature, spontaneous physical activity, systolic and diastolic blood pressure that later decreased, except for the systolic blood pressure. The results show that the dose level for long-lasting signs of intoxication to develop in the rat, in terms of effects on spontaneous physical activity, body temperature and cardiovascular function, was reached after a single oral dose of caffeine at 45 mg/kg b.w.

Nicotine accumulation in the mouse brain is age-dependent and is quantitatively different in various segments.

Mice, varying from newborn to adult mice, were injected intraperitoneally with 1 mg/kg of 14C-nicotine. The nicotine concentration in blood and different segments of the brain (Cerebellum, Pons and Medulla oblongata, Midbrain, B. olfactory, Hypothalamus, Hippocampus and Cortex) was determined in newborn (0-day old); in 1-, 3-, 5-, 7-, 9-, 12- and 17-day old; and in adult (26-day old) mice. The nicotine concentration in the blood did not differ in mice aged 0-12 days, but the concentration thereafter decreased substantially until adult age. The decrease was associated with metabolism of nicotine as evidenced by cotinine formation, as well accumulation in different regions of the brain. Irrespective of the small continuous brain growth from day 1 until adult age, the age dependent nicotine uptake was dramatically increased in all segments of the brain between 9 and 12 days of age. However, the various brain regions showed differences in magnitude of growth and age-dependent changes in the distribution of nicotine. The relative nicotine concentration in Pons Med. obl. seems to be high in young mice until 9 days of age; thereafter, the concentration decreases in comparison to the other regions. Conversely, the relative concentration in the hippocampus and cortex rises from day 9 to 17 of age. The present results show that the ability of the brain to accumulate nicotine increases with age, reaching a peek at day 12 of age. Furthermore, this study for the first time shows that the age-dependent brain nicotine accumulation is quantitatively different in the various segments of the brain.

Effects of a superantigen-antibody recombinant fusion protein (r-C242 Fab-SEA) on toxicological responses in the anaesthetised rabbit.

The objective was to study toxin-induced effects on physiological parameters in the rabbit and whether these parameters show dose-response and co-variation after administration of a recombinant fusion protein between staphylococcal enterotoxin (SE) and the Fab fragment of an antibody. Rabbits are very sensitive to SE toxins and the cardiovascular and immune effects are similar to those observed in septic shock in man. The test compound, r-C242 Fab-SEA, was administered intravenously to anaesthetised New Zealand white rabbits at doses in the range of 0.00005-50 microg/kg. All rabbits were checked for titres of anti-SEA antibodies before entering the experiment, since they could neutralise the effect of the test compound. Heart rate, blood pressure and body temperature were continuously monitored before and during 6 h after dosing. Immediately before the start of administration and 3 and 6 h during the experiment, blood gases (pO(2) and pCO(2)), pH, haematology, clinical chemistry, cytokine response (TNF-alpha) and trace elements (Mn, Cu, Zn, Se, Ag, Cd, Hg and Pb) were measured. No mortality occurred, but at 50 microg/kg severe adverse clinical signs developed. The decrease in blood pressure was weakly dose-related. Heart rate, ECG, body temperature, pCO(2) and pH were not affected by the treatment. pO(2) tended to increase as a function of time, but not in relation to dose. WBC and PLT decreased dose dependently. TNF-alpha was not affected by the treatment. The major effects on clinical chemistry were a dose-dependent increase in AST and creatinine. Potassium and urea showed dose dependent increases, mainly at higher doses, though these changes were of less value for drug selection purposes. Trace element changes were observed, including an increase in Mn and a decrease of Zn at all doses. The Cu/Zn ratio decreased below normal at low doses, whereas at high doses in which adverse effects developed, it increased above normal. Post mortem examination revealed minimal to moderate dose-related granulocytic infiltrate in the lungs. The present study showed dose-response and co-variation between several changes in cardiovascular, haematology, clinical chemistry and trace element parameters during the initial phase of toxin-induced effects preceding a possible lethal endpoint and associated patho-physiological changes.

Effects of rhIGF-I and insulin-induced hypoglycaemia on cardiovascular parameters recorded with telemetry in the conscious dog.

Using telemetry, the effects on cardiovascular parameters after single intravenous administration (0.5 mg/kg) of recombinant human insulin-like growth factor-I (rhIGF-I) were studied in conscious and unrestrained dogs. Insulin (1.1 IU/kg) was used as a reference compound. Telemetry transmitters were implanted subcutaneously with a pressure catheter in the femoral artery and electrodes for ECG subcutaneously. Cardiovascular effects and changes in blood glucose levels induced with rhlGF-I were similar to those induced with insulin. Heart rate increased continuously for about 90 min. after treatment, regardless of compound. Thereafter, heart rate slowly decreased but did not fully reach predose values 4 hr after treatment. Both systolic and diastolic blood pressure decreased continuously for about 90 min. and remained low for up to 4 hr after treatment. Treatment with rhIGF-I or insulin did not influence dp/dt values. Treatment with glucose intravenously to abolish the rhIGF-I-induced hypoglycaemia reduced the heart rate, but caused a substantial increase in dp/dt and a slight increase in blood pressure. RhIGF-I and insulin induced an almost identical onset and degree of hypoglycaemia. Blood glucose reached a minimum level 1 hr after treatment and was almost returned to normal 4 hr after treatment. There was an increase in the amplitude of the T-waves, though this effect occurred earlier and was longer lasting with insulin than with rhIGF-I. After 4 hr, the T-wave amplitude was normal with rhIGF-I but remained high with insulin. These T-wave effects were probably due to an increase in the transport of potassium or calcium since they decreased in plasma. This suggests that the effects of rhIGF-I and insulin are highly comparable and that the cardiovascular changes induced by rhIGF-I are likely caused by its insulin-like activity. As shown by the recorded cardiovascular responses induced by rhIGF-1 and insulin, the telemetric recording system makes it possible to evaluate the effects of different drugs in a continuous way that is not possible with conventional techniques. This new telemetric technique can be of significant importance in the process of future drug development.

A new screening model for safety evaluation of superantigen-antibody recombinant fusion proteins (mAb Fab-SEA/E) using telemetric monitoring in conscious rabbits.

INTRODUCTION: Carcinoma recognising monoclonal antibodies (mAb) and mutated forms of the T-cell-activating bacterial staphylococcal enterotoxin A/E (SEA/E) have been combined in single hybrid constructs (mAb Fab-SEA/E). By introducing substitutions in an MHC class II binding site, these harmful toxins can be converted into tolerable immunotoxins. Rabbits and humans are sensitive to SE toxins, and cardiovascular effects in rabbits are similar to those seen in septic shock in man. A new screening model using telemetry in conscious rabbits was applied in the safety evaluation of different mAb Fab-SEA/E constructs administered intravenously. METHODS: Telemetry transmitters were implanted in the peritoneal cavity of animals with a pressure catheter in the aorta and electrodes for ECG recording subcutaneously following administration of mAb Fab-SEA/E constructs intravenously. RESULTS: The responses in body temperature, heart rate, and blood pressure varied depending on the treatment regimen and the mutations of the drug given. For example, 25 micro g/kg of C215 Fab-SEAmut9 were given as a first treatment cycle on days 1, 5, and 7 and as a second treatment cycle on days 13-15. The first dose induced high fever, whereas the second and third doses induced fever responses more rapidly and were of lower and shorter duration. The second treatment cycle, starting on day 13, did not induce any responses probably due to anti-SEA antibodies formed because of the treatment. Another construct, 5T4 Fab-SEA/E-11 at 50 micro g/kg, induced a similar response as C215 Fab-SEAmut9 on days 1, 5, and 7. In this case, the pharmacologic response was still present on days 13-15, though no clinical signs developed or no formation of anti-SEA antibodies occurred. When 50 micro g/kg of 5T4 Fab-SEA/E-11 was administered once daily for 4 days, body temperature after the first dose increased slowly during the first 24 h, whereas the second to fourth doses induced more rapid and higher responses. The fourth dose of another compound, K305 Fab-SEA/E-11 (50 micro g/kg), induced an even more pronounced response both in magnitude and in duration as well as in adverse clinical signs. DISCUSSION: By using continuous telemetric registration in the rabbit as a tool in superantigen-antibody (mAb Fab-SEA/E) drug selection, it has been possible to evaluate the dynamics of drug-induced immune effects (fever) and concomitant engagement of the cardiovascular system, conditions that are essential before clinical trials can be initiated.