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

Cardiovascular and Locomotor Effects of Binary Mixtures of Common "Bath Salts" Constituents: Studies with Methylone, MDPV, and Caffeine in Rats

Background and Purpose

The use of "Bath Salts" drug preparations has been associated with high rates of toxicity and death. Preparations often contain mixtures of drugs including multiple synthetic cathinones or synthetic cathinones and caffeine; however, little is known about whether interactions among "Bath Salts" constituents contribute to the adverse effects often reported in users.

Experimental Approach

This study used adult male Sprague-Dawley rats to characterize the cardiovascular effects, locomotor effects, and pharmacokinetics of methylone, MDPV, and caffeine, administered alone and as binary mixtures. Dose-addition analyses were used to determine the effect levels predicted for a strictly additive interaction for each dose pair.

Key Results

Methylone, MDPV, and caffeine increased heart rate and locomotion, with methylone producing the largest increase in heart rate, MDPV producing the largest increase in locomotor activity, and caffeine being the least effective in stimulating heart rate and locomotor activity. MDPV and caffeine increased mean arterial pressure, with caffeine being more effective than MDPV. The nature of the interactions between methylone and MDPV tended toward sub-additivity for all endpoints, whereas interactions between MDPV or methylone and caffeine tended to be additive or sub-additive for cardiovascular endpoints, and additive or supra-additive for increases in locomotion. No pharmacokinetic interactions were observed between individual constituents, but methylone displayed non-linear pharmacokinetics at the largest dose evaluated.

Conclusion and Implications

These findings demonstrate that the composition of "Bath Salts" preparations can impact both cardiovascular and locomotor effects and suggest that such interactions among constituent drugs could contribute to the "Bath Salts" toxidrome reported by human users.

Caffeine: cardiorespiratory effects and tissue protection in animal models

OBJECTIVE

The aim of this review is to analyze the cardiorespiratory and tissue-protective effects of caffeine in animal models. Peer-reviewed literature published between 1975 and 2021 was retrieved from CAB Abstracts, PubMed, ISI Web of Knowledge, and Scopus. Extracted data were analyzed to address the mechanism of action of caffeine on cardiorespiratory parameters (heart rate and rhythm), vasopressor effects, and some indices of respiratory function; we close this review by discussing the existing debate on the research carried out on the effects of caffeine on tissue protection. Adenosine acts through specific receptors and is a negative inotropic andchronotropic agent. Blockage of its cardiac receptors can cause tachycardia (with arrhythmogenic potential) due to the intense activity of β1 receptors. In terms of tissue protection, caffeine produces inhibition of hyperoxia-induced pulmonary inflammation by decreasing proinflammatory cytokine expression in animal models.

CONCLUSION

The protection that caffeine provides to tissues is not limited to the CNS, as studies have demonstrated that it generates attenuation of inflammatory effects in pulmonary tissue, where it inhibits the effects of some pro-inflammatory cytokines and prevents functional and structural changes.

Review of animal studies on the cardiovascular effects of caffeine

To address the safety of caffeine levels in energy drinks, we previously conducted a detailed evaluation of epidemiology studies in humans consuming coffee/caffeine, in which we assessed multiple health effects (unpublished). To further evaluate the effects of caffeine on the cardiovascular system, we turned to animal studies, which often use pure caffeine (not coffee), frequently at higher doses than those typical of human exposure. We identified key scientific studies and reviews in which effects of coffee or caffeine were evaluated in animals by conducting a comprehensive PubMed literature search and analyzing the results. We found that the human equivalent dose (HED) for the no observed adverse effect level (NOAEL) for cardiovascular effects was 260 mg caffeine (2-3 cups of coffee) for a single dose of caffeine for a 70-kg adult, while the lowest observed adverse effect level (LOAEL) was 770 mg (7-8 cups of coffee) for a 70-kg adult. Overall, the doses associated with possible adverse cardiovascular effects were more than either the amount of caffeine consumed over a 24-hour period in two regular energy shots (400 mg/day) or the amount in two extra strength energy shots (460 mg/day).

Cardiovascular effects of long-term caffeine administration in aged rats

AIM

To evaluate the possible beneficial effect of long-term caffeine administration on cardiovascular system in aged rats.

METHODS

This study was carried out on 20 senile male albino rats, aged 18-20 months. Rats were divided into caffeine-treated group, which received 25 mg/kg caffeine by gavage daily for 6 weeks, and control group. All rats were subjected to the following in vivo measurements: body weight, arterial blood pressure, heart rate and ECG recording. In vitro measurements included studying isolated hearts in a Langendorff apparatus for their intrinsic properties as well as plasma levels of lipids, malondialdehyde and nitrate.

RESULTS

Caffeine administration to aged rats significantly enhanced the baseline and maximum values achieved in response to isoproterenol infusion in isolated heart preparation for both maximum rate of tension development (dT/dt max) and time to peak tension (TPT). The responses of hearts isolated from caffeine group to the three doses of isoproterenol infusion also showed a significantly higher dT/dt max with shorter TPT and half relaxation time (1/2 RT) compared to controls. Plasma nitrate was significantly increased and ECG recording was nonsignificantly affected in caffeine group. The plasma levels of total cholesterol, LDL cholesterol as well as in vivo heart rate and systolic, diastolic and mean arterial blood pressures were all significantly increased associated with a significant decrease in HDL cholesterol in caffeine group.

CONCLUSION

Long-term caffeine administration in aged rats increased cardiac inotropy, lusitropy and preserved NO level, which points to a promising potential favorable effect on cardiac intrinsic properties.

Intraoperative vital and haemodynamic monitoring using an integrated multiple-channel monitor in rats

The aim of this study is to give a hands-on description of the successful monitoring procedure established for extended liver resections and liver transplantations in rats and to provide the typical range of data as obtained before and after a hepatobiliary surgical procedure (right median hepatic vein [RMHV] ligation) in healthy male Lewis rats. All manipulations were performed in anaesthetized (3% isoflurane in O2 1 L/min) healthy male Lewis rats (250–350 g) with an integrated multiple-channel intraoperative monitor (Powerlab® system) using a series of sensors for data acquisition. Vital parameters (body temperature, electrocardiogram, respiratory rate and heart rate), haemodynamic parameters (mean arterial blood pressure [MAP] and central venous pressure) and liver perfusion parameters (inferior hepatic venous pressure, portal vein pressure [PVP], blood flow of portal vein and inferior hepatic cava) were monitored. Catheters were placed in microsurgical technique after careful exposure guided by anatomical landmarks. Vascular incisions were closed with interrupted sutures. Complete instrumentation of animals was performed within 1 h. No specific complications occurred. Vital and haemodynamic parameters such as MAP (94 ± 16.2 mmHg) or portal pressure (9.6 ± 1.34 mmHg) were in the same range as known for humans (MAP = 100 mmHg, portal pressure = 5–10 mmHg), whereas parameters dependent on the size of the body or organ such as flow rates (portal blood flow = 16.2 ± 6 mL/min) were obviously different compared with those of humans (portal blood flow = 800 mL/min). In conclusion, the normal range for vital, haemodynamic and liver perfusion parameters was reported as reference values to allow quality control for future surgical hepatobiliary research projects. As the procedure can be easily learned, the extensive intraoperative monitoring can be used routinely.

Exploitation of secondary metabolites by animals: A response to homeostatic challenges

We propose that the exploitation of the bioactive properties of secondary metabolites (SMs) by animals can provide a "treatment" against various challenges that perturb homeostasis in animals. The unified theoretical framework for the exploitation of SMs by animals is based on a synthesis of research from a wide range of fields and although it is focused on providing generalized predictions for herbivores that exploit SMs of plants, predictions can be applied to understand the exploitation of SMs by many animals. In this review, we argue that the probability of SM exploitation is determined by the relative difference between the cost of a homeostatic challenge and the toxicity of the SM and we provide various predictions that can be made when considering behavior under a homeostatic perspective. The notion that animals experience and respond to costly challenges by exploiting therapeutic SMs provides a relatively novel perspective to explain foraging behavior in herbivores, specifically, and behavior of animals in general. We provide evidence that animals can exploit the biological activity of SMs to mitigate the costs of infection by parasites, enhance reproduction, moderate thermoregulation, avoid predation, and increase alertness. We stress that a better understanding of animal behavior requires that ecologists look beyond their biases that SMs elicit punishment and consider a broader view of avoidance or selection of SMs relative to the homeostatic state. Finally, we explain how understanding exploitation of SMs by animals could be applied to advance practices of animal management and lead to discovery of new drugs.

Physiological roles of A1 and A2A adenosine receptors in regulating heart rate, body temperature, and locomotion as revealed using knockout mice and caffeine

Heart rate (HR), body temperature (Temp), locomotor activity (LA), and oxygen consumption (O(2)C) were studied in awake mice lacking one or both of the adenosine A(1) or A(2A) receptors (A(1)R or A(2A)R, respectively) using telemetry and respirometry, before and after caffeine administration. All parameters were lower during day than night and higher in females than males. When compared with wild-type (WT) littermates, HR was higher in male A(1)R knockout (A(1)RKO) mice but lower in A(2A)RKO mice and intermediate in A(1)-A(2A)R double KO mice. A single dose of an unselective beta-blocker (timolol; 1 mg/kg) abolished the HR differences between these genotypes. Deletion of A(1)Rs had little effect on Temp, whereas deletion of A(2A)Rs increased it in females and decreased it in males. A(1)-A(2A)RKO mice had lower Temp than WT mice. LA was unaltered in A(1)RKO mice and lower in A(2A)RKO and A(1)-A(2A)RKO mice than in WT mice. Caffeine injection increased LA but only in mice expressing A(2A)R. Caffeine ingestion also increased LA in an A(2A)R-dependent manner in male mice. Caffeine ingestion significantly increased O(2)C in WT mice, but less in the different KO mice. Injection of 30 mg/kg caffeine decreased Temp, especially in KO mice, and hence in a manner unrelated to A(1)R or A(2A)R blockade. Selective A(2B) antagonism had little or no effect. Thus A(1)R and A(2A)R influence HR, Temp, LA, and O(2)C in mice in a sex-dependent manner, indicating effects of endogenous adenosine. The A(2A)R plays an important role in the modulation of O(2)C and LA by acute and chronic caffeine administration. There is also evidence for effects of higher doses of caffeine being independent of both A(1)R and A(2A)R.

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.

Nonexercise activity thermogenesis--liberating the life-force

Obesity occurs when energy intake exceeds energy expenditure over a protracted period of time. The energy expenditure associated with everyday activity is called NEAT (Nonexercise activity thermogenesis). NEAT varies between two people of similar size by 2000 kcal day(-1) because of people's different occupations and leisure-time activities. Data support the central hypothesis that NEAT is pivotal in the regulation of human energy expenditure and body weight regulation and that NEAT is important for understanding the cause and effective treatment for obesity.