Detection and distribution of opioid peptide receptors in porcine myocardial tissue.

There is growing evidence that opioid peptide receptors (OPRs) play an important role in cardiovascular function. Many studies have been conducted in swine, in view of their anatomic and physiologic similarities to humans. Until now, the presence and particularly distribution of OPRs has been unclear. Porcine myocardial tissue was obtained from both the left and right atria and ventricles. Expression of mRNA for µ-, δ- and κ-OPR was determined by reverse transcription PCR. OPR proteins were detected by Western blot, distribution and cellular location were identified using immunohistochemistry. Homogenous expression of mRNA and protein for δ- and κ-OPRs were demonstrated in all porcine myocardial tissue tested, whereas expression of µ-OPR mRNA was not demonstrated in any of the tissues tested. This study demonstrates the expression of δ- and κ-OPRs in porcine myocardial tissue. No differences in distribution of δ- and κ-OPRs were found between the four heart cavities. Modulation of cardiac function by δ- and κ-OPR agonists or antagonists is therefore possible, while µ-OPR-mediated direct cardiac effects appear unlikely, due to nonexpression of the receptor. This study demonstrates that porcine studies can further elucidate the role of OPRs in cardiac (patho-)physiology.

Dual-lumen catheters for continuous venovenous hemofiltration: limits for blood delivery via femoral vein access and a potential alternative in an experimental setting in anesthetized pigs.

INTRODUCTION: Small intravascular volume, pathophysiological hemorheology, and/or low cardiac output [CO] are assumed to reduce available blood flow rates via common dual-lumen catheters (except for those with a right atrium catheter tip position) in the critically ill patient. We performed an experimental animal study to verify these assumptions. METHODS: Anesthetized, ventilated pigs (35 to 50 kg) were allocated to different hemorheological conditions based on the application of different volume substitutes (that is, colloids and crystalloids, n = 6 to 7 per volume substitute). In a second step, allocation to the final study group was performed after the determination of the highest values for access flow (Qa) via an axial dual-lumen catheter (11 French, 20 cm long, side holes) placed in the femoral vein. High Qa rates (>300 ml/minute) were allocated to the dual-lumen catheter group; low Qa rates were switched to a 'dual-vein approach' using an alternative catheter (8.5-French sheath) for separate blood delivery. Hemodynamics (CO and central venous pressure [CVP]) and blood composition (blood cell counts, plasma proteins, and colloid osmotic pressure) were measured. Catheter tip positions and vessel diameters were exemplified by computed tomography. RESULTS: Forty-four percent of the animals required an alternative vascular access due to only minimal Qa via the dual-lumen catheter. Neither hemorheologically relevant aspects nor CO and CVP correlated with the Qa achievable via the femoral vein access. Even though the catheter tip of the alternative catheter provided common iliac vein but not caval vein access, this catheter type enabled higher Qa than the dual-lumen catheter positioned in the caval vein. CONCLUSION: With respect to the femoral vein approach, none of the commonly assumed reasons for limited Qa via the arterial line of an axial dual-lumen catheter could be confirmed. The 8.5-French sheath, though not engineered for that purpose, performed quite well as an alternative catheter. Thus, in patients lacking right jugular vein access with tip positioning of large-French dual-lumen catheters in the right atrium, it would be of interest to obtain clinical data re-evaluating the 'dual-vein approach' with separate blood delivery via a tip-hole catheter in order to provide high-volume hemofiltration.