Seasonal and environmental influences upon the diurnal heart-rate pattern in wild rabbits living under seminatural conditions

Effects of buprenorphine on body temperature, locomotor activity and cardiovascular function when assessed by telemetric monitoring in rats

Buprenorphine is a potent analgesic commonly used clinically in humans and rodents experiencing severe pain. However, effects of therapeutic doses on locomotor activity and the cardiovascular system have not been studied in conscious animals. The effects of buprenorphine were therefore evaluated in this study using telemetric monitoring in conscious animals. Telemetry transmitters were implanted in the peritoneal cavity of Wistar rats with a pressure catheter in the aorta and electrodes for electrocardiogram (ECG) recording subcutaneously. After a single subcutaneous administration of saline, each rat was administered single subcutaneous doses of 0.006, 0.03 or 0.15 mg/kg body weight (bw) of buprenorphine. During a 10 h period after administration, buprenorphine induced a varying dose-dependent increase in body temperature, heart rate, dP/dt and systolic-diastolic blood pressure, as well as a corresponding decrease in QT time. At high dose, however, QT time was still decreased 24 h post-administration, but no arrhythmias or visual changes were observed in the ECG complex. Body temperature and heart rate increased at the high dose of buprenorphine, even at 20-24 h after administration. Moreover, the high dose of buprenorphine induced a biphasic response in diastolic blood pressure, with an early and pronounced increase that, at 14 h after administration, reversed to a decrease, failing to normalize within 24 h post-dosage. The results indicate that buprenorphine induces long-lasting effects (such as body temperature and cardiovascular effects) in the rat after a single subcutaneous dose at 0.15 mg/kg bw.

Cardiovascular responses to locomotor activity and feeding in unrestrained three-toed sloths, Bradypus variegatus

Heart rate (HR) and systolic (SBP), diastolic (DBP) and mean (MBP) blood pressure were recorded by biotelemetry in nine conscious unrestrained sloths for 1 min every 15 min over a 24-h period. The animals were allowed to freely move in an acoustically isolated and temperature-controlled (24 +/- 1 degree C) experimental room with light-dark cycle (12/12 h). Behavior was closely monitored through a unidirectional visor and classified as resting (sitting or suspended), feeding (chewing and swallowing embauba leaves, Cecropia adenops), or locomotor activity around the tree trunk or on the room floor. Locomotor activity caused statistically significant increases in SBP (+8%, from 121 +/- 22 to 131 +/- 18 mmHg), DBP (+7%, from 86 +/- 17 to 92 +/- 10 mmHg), MBP (+8%, from 97 +/- 19 to 105 +/- 12 mmHg), and HR (+14%, from 84 +/- 15 to 96 +/- 15 bpm) compared to resting values, indicating a possible major influence of the autonomic nervous system on the modulation of cardiac function during this behavior. During feeding, the increase in blood pressure was even higher (SBP +27%, from 119 +/- 21 to 151 +/- 21 mmHg; DBP +21%, from 85 +/- 16 to 103 +/- 15 mmHg; MBP +24%, from 96 +/- 17 to 119 +/- 17 mmHg), while HR remained at 14% (from 84 +/- 15 to 96 +/- 10 bpm) above resting values. The proportionally greater increase in blood pressure than in HR during feeding suggests an increase in peripheral vascular resistance as part of the overall response to this behavior.

Cardiovascular effects of xylazine recorded with telemetry in the dog

Cardiovascular effects of xylazine have not been studied with telemetry in dogs. In the present study, the effects on cardiovascular parameters after intramuscular (i.m.) administration of 2.0 mg/kg xylazine were studied via telemetry in unrestrained dogs. Telemetry transmitters were implanted subcutaneously (s.c.) with a pressure catheter in the femoral artery. Cardiovascular effects and body temperature effects were assessed after i.m. administration of xylazine. Heart rate decreased for about 10 min and was continuously depressed during 60 min. Thereafter, heart rate slowly increased but had not fully reached pre-dose values 4 h after treatment. Both systolic and diastolic blood pressure increased immediately after administration of xylazine. The systolic blood pressure showed a peak increase for about 5-10 min and then decreased below the baseline value not normalizing within 90 min. The diastolic blood pressure peaked 5-10 min after xylazine administration but did not return to baseline level until 50 min after administration. Body temperature decreased continuously for about 90 min and remained low for more than 4 h after treatment. An additional administration of xylazine to the same individuals after a recovery period of 4 weeks induced exactly the same response in systolic and diastolic blood pressure and in heart rate. By using the telemetric recording system it was possible to continuously evaluate xylazine-induced cardiovascular responses in a way that is not possible with conventional techniques.

Ca2+-activated Cl- current reduces transmural electrical heterogeneity within the rabbit left ventricle

OBJECTIVE

Various cationic membrane channels contribute to the heterogeneity of action potential configuration between the transmural layers of the left ventricle. The role of anionic membrane channels is less intensively studied. We investigated the role of the Ca2+-activated Cl- current, ICl(Ca), in transmural electrical heterogeneity.

METHODS AND RESULTS

We determined the density of ICl(Ca) and its physiological role in subepicardial and subendocardial ventricular myocytes of rabbit using the patch-clamp technique. ICl(Ca) was measured as the 4,4'diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) sensitive current. The current-voltage relationships and the densities of ICl(Ca) were similar in subepicardial and subendocardial myocytes. However, the functional role of ICl(Ca) exhibited striking differences. In subendocardial myocytes, blockade of ICl(Ca) by DIDS increased action potential duration (APD) significantly at all measured stimulus frequencies (3.33-0.2 Hz). In subepicardial myocytes, ICl(Ca) blockade increased APD only at 3.33 Hz, but not at the lower stimulus frequencies. At 1 Hz, ICl(Ca) blockade in subepicardial myocytes only caused an APD increase when the transient outward K+ current, Ito1, was blocked.

CONCLUSIONS

The densities and gating properties of ICl(Ca) are similar in subepicardial and subendocardial myocytes. ICl(Ca) contributes to APD shortening in subendocardial, but not in subepicardial myocytes except at 3.33 Hz. These differences in functional expression of ICl(Ca) reduce the electrical heterogeneity in rabbit left ventricle.

The daily pattern of cardiovascular parameters in Kurosawa and Kusanagi-Hypercholesterolemic (KHC) rabbits

We studied characteristics of the daily pattern of heart rate (HR), blood pressure (BP), body temperature (BT), and locomotor activity (LA) in conscious and unrestrained Kurosawa and Kusanagi-Hypercholesterolemic (KHC) rabbits and age-matched normal Japanese white (JW) rabbits, using a telemetry system. In all JW rabbits, nocturnal patterns were observed in HR, BT and LA. In the 5 months group of KHC rabbits, however, diurnal rhythm was observed in HR, and in the 10 months group of KHC rabbits, it was also shown in LA. The nocturnal pattern was observed only in BT in 10 months KHC rabbits. Mean blood pressure (MBP) in JW and KHC rabbits showed no clear daily pattern. The mean daily values of HR and BT were not altered between the 5 months and 10 months groups in KHC rabbits, although those in JW were lower in the 10 months group than in the 5 months group. Moreover, the daily values of HR and MBP in KHC rabbits tended to be higher than those in the age-matched JW rabbits. The pulse pressure in the 10 months group of KHC rabbits tended to be greater than the 5 months groups of KHC and JW rabbits. Furthermore, short-term variabilities in BP in the 5 months KHC rabbits were significantly lower than those in the other groups. From these results, it is suggested that the cardiovascular function, including the autonomic nervous function is altered with the development of atherosclerosis in KHC rabbits.

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.

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.

Diversity and development of circadian rhythms in the European rabbit

Three main concerns underlie this review: 1) The need to draw together the widely dispersed information available on the circadian biology of the rabbit. Although the rabbit is a classic laboratory mammal, this extensive body of information is often overlooked by chronobiologists, and despite several advantages of this species. In terms of its general biology the rabbit is the best studied laboratory mammal in the wild, it demonstrates a wide variety of robust circadian functions, and being a lagomorph, it provides a useful comparison with more commonly studied rodent species. 2) The need to more fully exploit a developmental approach to understanding circadian function, and the particular suitability of the rabbit for this. Female rabbits only visit their altricial young for a few minutes once every 24 h to nurse, and survival of the young depends on the tight circadian-controlled synchronization in behavior and physiology of the two parties. Patterns of circadian rhythmicity in neonatal pups associated with nursing do not form a smooth continuum into weaning and adult life, and may reflect the action of separate mechanisms operating in their own right. 3) Using information from the first two points, to emphasize the diversity and complexity of circadian rhythms underlying behavioral and physiological functions in adult and developing mammals. Information accruing on circadian functions in the rabbit makes it increasingly difficult to account for these in terms of one or two regulatory mechanisms or "oscillators." Thus, it is argued that in addition to the reductionist, molecular approaches currently dominating much of chronobiology, the study of circadian systems as emergent characteristics of whole organisms operating in complex environments merits special attention.

24-hour recordings of blood pressure, heart rate and behavioural activity in rabbits by radio-telemetry: effects of feeding and hypertension

We used radio-telemetry to measure 24-hour rhythms of systolic, diastolic and mean blood pressure, heart rate and behavioural activity in conscious rabbits, which were maintained under normal day/night rhythms and restricted feeding. Over three consecutive days, all variables showed little change between day-period and night-period, except for a pronounced rise in the afternoon, coinciding with the presentation of pellet food. Mean blood pressure increased during this period from baseline values between 78-82 mm Hg to a peak of 89-91 mm Hg. At the same time heart rate rose from baseline values of 147-161 b/min to a peak of 206-234 b/min and behavioural activity scores rose from 11-31 counts/h to a peak of 52-81 counts/h. Changing the time at which pellet food was presented to the rabbits from the early afternoon to the early morning, caused a complete and immediate shift of the peak of blood pressure and heart rate to the morning period. Chronic intravenous infusion of angiotensin II caused a significant increase in blood pressure (24-hour average: 80 +/- 1 vs. 114 +/- 7 mm Hg) but did not alter basal heart rate or behavioural activity. The increase in heart rate and blood pressure seen with food presentation was attenuated with angiotensin II infusion. These data show that in rabbits diurnal changes in blood pressure, heart rate and activity were determined to a large extent by timed feeding. In addition, in rabbits with angiotensin-induced hypertension the food-induced changes in blood pressure and heart rate were blunted.

Circadian and short-term variabilities in blood pressure and heart rate measured by telemetry in rabbits and rats

Blood pressure (BP) and heart rate (HR) were measured by telemetry in conscious unrestrained rabbits to clarify the profile of their variabilities. The variabilities were assessed for two periods, 24 h (circadian rhythm) and 1 h (short-term variability), and compared with those in rats. BP and HR in rabbits were lower than those in rats but the circadian rhythms in rabbits showed nocturnal patterns as is the case in rats. In contrast, short-term variabilities in BP in rabbits were considerably larger than those in rats. The short-term variability in BP in rabbits was suppressed by alpha-adrenergic blocking without changes in basal values but not by beta-adrenergic blocking or angiotensin converting enzyme inhibition. These results demonstrate the need to take the unique characteristics of short-term variability in BP in rabbit into consideration when the circadian rhythm is focused on and that the short-term variability in BP in rabbits is caused mainly by activation of alpha-adrenergic receptors.

Ethophysiological responses to overwinter food shortage in wild European rabbits

Wild European rabbits studied under seminatural conditions turned out to have about 30% lower heart rates during periods of overwinter food shortage than during periods with access to green forage or pelleted rabbit chow. Concomitant changes in the animals' metabolic rate (ADMR), body weight, blood sugar level, and foraging activity clearly indicate that this heart rate reduction is a sign of starvation due to insufficient food quality. Telemetered body temperature, on the other hand, was amazingly stable in most subjects, even during overwinter food shortage. These data are discussed with respect to nutritional requirements and possible mechanisms of energy conservation in wild European rabbits.

Long-term heartrate responses to social stress in wild European rabbits: predominant effect of rank position

The long-term mean heartrates of wild European rabbits living in a seminatural environment have been studied based on more than 1500 days of radiotelemetrical heartrate recordings. Significant differences between the heartrate levels of dominant and subordinate individuals have been found. Subordinate rabbits show chronically elevated heartrate that cannot be explained by limited access to burrow shelter or by the cumulative effect of heartrate reactions during aggressive encounters. If a subordinate rabbit achieves a dominant position, its heartrate is gradually adjusted to the lower level characteristic of dominant individuals. These results are discussed with respect to the consequences of dominance in species with different social systems.

Developmental constraints on the expression of behavioral and heart-rate orienting responses: II. The role of ambient temperature

The effect of ambient temperature on the expression of behavioral and heart-rate orienting responses to a novel olfactory stimulus was examined in rats 1-18 days of age. There was no effect of ambient temperature on the behavioral orienting responses at any age. Ambient temperature did influence the expression of the heart-rate orienting response and did so differentially as a function of age. The implications of these findings for developmental models of attention and cognition are discussed.

Longterm heartrate telemetry in small mammals: a comprehensive approach as a prerequisite for valid results

This paper describes a miniature telemetry system which is capable of precise, reliable longterm registration of heartrate (HR) in animals as small as laboratory mice. The ECG-transmitters have a weight of 0.9-1.5 g and a respective lifetime of 3-6 months depending on battery size. With suitable receiving antennas, transmitting range is sufficient for continuous reception in 200 m2 enclosures. The radio signals are demodulated in a signal processor and the ECG is converted to HR on the base of single interbeat intervals. General technical problems of telemetry like miniaturization, performance control, HR acquisition and artifact distinction are discussed. The experimental approach emphasizes the necessity of continuous registration of HR as a reference for experimental responses. Longterm shifts of HR due to social and nonsocial influences as well as experimental feedback effects are demonstrated and discussed.