Dual implantation of a radio-telemeter and vascular access port allows repeated hemodynamic and pharmacological measures in conscious lean and obese rats

Expansion of physiological knowledge increasingly requires examination of processes in the normal, conscious state. The current study describes a novel approach combining surgical implantation of radio-telemeters with vascular access ports (VAPs) to allow repeated hemodynamic and pharmacological measures in conscious rats. Dual implantation was conducted on 16-week-old male lean and obese Zucker rats. Continued viability one month after surgery was observed in 67% of lean and 44% of obese animals, giving an overall 54% completion rate. Over the five-week measurement period, reliable and reproducible basal mean arterial pressure and heart rate measures were observed. VAP patency and receptor-independent vascular reactivity were confirmed by consistent hemodynamic responses to sodium nitroprusside (6.25 µg/kg). Acutely, minimal hemodynamic responses to repeated bolus administration of 0.2 mL saline indicated no significant effect of increased blood volume or administration stress, making repeated acute measures viable. Similarly, repeated administration of the β-adrenoceptor agonist dobutamine (30 µg/kg) at 10 min intervals resulted in reproducible hemodynamic changes in both lean and obese animals. Therefore, our study demonstrates that this new approach is viable for the acute and chronic assessment of hemodynamic and pharmacological responses in both lean and obese conscious rats. This technique reduces the demand for animal numbers and allows hemodynamic measures with minimal disruption to animals' welfare, while providing reliable and reproducible results over several weeks. In conclusion, dual implantation of a radio-telemeter and VAP introduces a valuable technique for undertaking comprehensive studies involving repeated pharmacological tests in conscious animals to address important physiological questions.

Sevoflurane-induced cardioprotection depends on PKC-alpha activation via production of reactive oxygen species

BACKGROUND

We previously demonstrated the involvement of the Ca2+-independent protein kinase C-delta (PKC-delta) isoform in sevoflurane-induced cardioprotection against ischaemia and reperfusion (I/R) injury. Since sevoflurane is known to modulate myocardial Ca2+-handling directly, in this study we investigated the role of the Ca2+-dependent PKC-alpha isoform in sevoflurane-induced cardioprotective signalling in relation to reactive oxygen species (ROS), adenosine triphosphate-sensitive mitochondrial K+ (mitoK+(ATP)) channels, and PKC-delta.

METHODS

Preconditioned (15 min 3.8 vol% sevoflurane) isolated rat right ventricular trabeculae were subjected to I/R, consisting of 40 min superfusion with hypoxic, glucose-free buffer, followed by normoxic glucose-containing buffer for 60 min. After reperfusion, contractile recovery was expressed as percentage of force development before I/R. The role of PKC-alpha, ROS, mitoK+(ATP) channels, and PKC-delta was established using the following pharmacological inhibitors: Go6976 (GO; 50 nM), n-(2-mercaptopropionyl)-glycine (MPG; 300 microM), 5-hydroxydecanoic acid sodium (5HD; 100 microM), and rottlerin (ROT; 1 microM).

RESULTS

Preconditioning of trabeculae with sevoflurane improved contractile recovery after I/R [65 (3)% (I/R + SEVO) vs 47 (3)% (I/R); n = 8; P < 0.05]. This cardioprotective effect was attenuated in trabeculae treated with GO [42 (4)% (I/R + SEVO + GO); P > 0.05 vs (I/R)]. In sevoflurane-treated trabeculae, PKC-alpha translocated towards mitochondria, as shown by immunofluorescent co-localization analysis. GO and MPG, but not 5HD or ROT, abolished this translocation.

CONCLUSIONS

Sevoflurane improves post-ischaemic contractile recovery via activation of PKC-alpha. ROS production, but not opening of mitoK+(ATP) channels, precedes PKC-alpha translocation towards mitochondria. This study shows the involvement of Ca2+-dependent PKC-alpha in addition to the well-established role of Ca2+-independent PKC isoforms in sevoflurane-induced cardioprotection.

Increased coronary perfusion augments cardiac contractility in the rat through stretch-activated ion channels

The role of stretch-activated ion channels (SACs) in coronary perfusion-induced increase in cardiac contractility was investigated in isolated isometrically contracting perfused papillary muscles from Wistar rats. A brief increase in perfusion pressure (3-4 s, perfusion pulse, n = 7), 10 repetitive perfusion pulses (n = 4), or a sustained increase in perfusion pressure (150-200 s, perfusion step, n = 7) increase developed force by 2.7 +/- 1.1, 7.7 +/- 2.2, and 8.3 +/- 2.5 mN/mm(2) (means +/- SE, P < 0.05), respectively. The increase in developed force after a perfusion pulse is transient, whereas developed force during a perfusion step remains increased by 5.1 +/- 2.5 mN/mm(2) (P < 0.05) in the steady state. Inhibition of SACs by addition of gadolinium (10 micromol/l) or streptomycin (40 and 100 micromol/l) blunts the perfusion-induced increase in developed force. Incubation with 100 micromol/l N(omega)-nitro-L-arginine [nitric oxide (NO) synthase inhibition], 10 micromol/l sodium nitroprusside (NO donation) and 0.1 micromol/l verapamil (L-type Ca(2+) channel blockade) are without effect on the perfusion-induced increase of developed force. We conclude that brief, repetitive, or sustained increases in coronary perfusion augment cardiac contractility through activation of stretch-activated ion channels, whereas endothelial NO release and L-type Ca(2+) channels are not involved.

Decrease in coronary vascular volume in systole augments cardiac contraction

Coronary arterial inflow is impeded and venous outflow is increased as a result of the decrease in coronary vascular volume due to cardiac contraction. We evaluated whether cardiac contraction is influenced by interfering with the changes of the coronary vascular volume over the heart cycle. Length-tension relationships were determined in Tyrode-perfused rat papillary muscle and when coronary vascular volume changes were partly inhibited by filling it with congealed gelatin or perfusing it with a high viscosity dextran buffer. Also, myocyte thickening during contraction was reduced by placing a silicon tube around the muscle. Increasing perfusion pressure from 8 to 80 cmH2O, increased developed tension by approximately 40%. When compared with the low perfusion state, developed tension of the gelatin-filled vasculature was reduced to 43 +/- 6% at the muscle length where the muscle generates the largest developed tension (n = 5, means +/- SE). Dextran reduced developed tension to 73 +/- 6% (n = 6). The silicon tube, in low perfusion state, reduced the developed tension to 83 +/- 7% (n = 4) of control. Time-control and oxygen-lowering experiments show that the findings are based on mechanical effects. Thus interventions to prevent myocyte thickening reduce developed tension. We hypothesize that when myocyte thickening is prevented, intracellular pressure increases and counteracts the force produced by the contractile apparatus. We conclude that emptying of the coronary vasculature serves a physiological purpose by facilitating cardiomyocyte thickening thereby augmenting force development.

Emotional and footshock stimuli induce differential long-lasting behavioural effects in rats; involvement of opioids

Rats were exposed to either a footshock stimulus (FS) or emotional stimulus (ES, forced perception of another rat receiving footshocks) during a daily 10-min session for 5 consecutive days. The consequences of FS and ES on their behavioural responsiveness were assessed at different post-stress intervals using a small open-field. FS induced a decrease in ambulation, rearing and sniffing and an increased immobility in the small open field. These effects were present in rats tested immediately after the last session and remained present for at least 15 days. In contrast, ES induced a transient decrease in ambulation and rearing immediately after the last session, but in the period from half an hour until at least 15 days after the stimulus experience, an increase in ambulation, rearing and sniffing was observed. Exposure to one footshock per session for 5 consecutive days or to 10 footshocks in a single session also resulted in a long-lasting reduction in ambulation and sniffing and an increase in immobility. The former regime did not influence the behavioural response of ES rats, but the latter resulted in an increase in ambulation, rearing and sniffing in ES rats. Naloxone (1 mg/kg s.c.) pretreatment antagonized the increased behavioural activity of the ES rats whereas the activity of control and FS animals was not affected, suggesting an involvement of endogenous opioid systems in the behavioural responses observed in ES rats. It is suggested that the behavioural responses of the ES and FS animals are regulated by different mechanisms.