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Instability of endothelium-bound lipoprotein lipase activity in perfused rat hearts
Insights
Endothelium-bound cardiac lipoprotein lipase activity significantly decreases during rat heart perfusion. This loss of enzymatic function, approximately 2% per minute, occurs even when heart viability is maintained.
Area of Science:
- Cardiovascular Physiology
- Enzymology
- Biochemistry
Background:
- Endothelium-bound lipoprotein lipase (LPL) plays a crucial role in cardiac lipid metabolism.
- Maintaining consistent LPL activity is important for studies using heart perfusion techniques.
Purpose of the Study:
- To investigate the stability of cardiac lipoprotein lipase enzymatic activity during isolated rat heart perfusion.
- To determine the rate of LPL activity decline and factors influencing it.
Main Methods:
- Isolated rat hearts were perfused for 1 hour at 37°C, maintaining constant viability parameters.
- Lipoprotein lipase activity was measured using triolein emulsion and chylomicrons in the perfusate.
- Input-output differences in triacylglycerol content quantified lipase activity.
Main Results:
- Cardiac LPL activity decreased over the perfusion time, losing approximately 2% of its initial activity per minute.
- The presence of rat serum (10%) accelerated the decline in LPL activity.
- Minimal LPL activity was recovered in the outflow perfusate, suggesting inactivation or retention within the heart.
Conclusions:
- Cardiac lipoprotein lipase activity is not constant during heart perfusion and declines significantly over time.
- The initial step in the catabolism of cardiac LPL appears to be the loss of its enzymatic activity.
- Further research is needed to ascertain if the inactivated enzyme is released or remains bound to the endothelium.
Abstract:
The enzymatic activity of endothelium-bound lipoprotein lipase was measured in rat hearts perfused for 1 h at 37 degrees C. Viability parameters such as beating rate, flow rate, aortic pressure, and oxygen consumption were all kept strictly constant during the entire perfusion time. The lipase activity was determined by input-output difference of the triacylglycerol content in the nonrecirculating heart perfusate which contained either an artificial triolein emulsion or rat lymph chylomicrons. With either substrate, the lipase activity decreased with time: approximately 2% of initial lipase activity was lost per minute. The presence of rat serum (10%) in heart perfusate enhanced the rate at which the lipase activity disappeared. Only a small portion of the lipoprotein lipase activity, which was lost from the perfused heart, was recovered in the outflow perfusate. Our data demonstrate that, under our experimental conditions, the enzymatic activity of rat heart lipoprotein lipase does not remain constant during heart perfusion. Caution should therefore be taken by users of heart perfusion technique, especially for those who need constant lipoprotein lipase activity. The results suggest that the first step in the catabolic fate of endothelium-bound cardiac lipoprotein lipase is the loss of its catalytic activity. Whether the inactivated enzyme is released from the endothelium or remains in situ is not yet known.