Attenuation of the anti-contractile effect of cooling in the rat aorta by perivascular adipose tissue

1. In addition to providing mechanical support for blood vessels, the perivascular adipose tissue (PVAT) secretes a number of vasoactive substances and exerts an anticontractile effect. The main objective of this study was to find out whether the anticontractile effect of cooling in the rat aorta is affected by PVAT. Our hypothesis was that PVAT would enhance the anticontractile effect of cooling in the rat aorta.
2. Aorta segments, with or without PVAT, were used in this investigation. Cumulative concentration-response curves were established for phenylephrine at 37°C or 24°C. Phenylephrine (10^-9M – 10^-5M) induced concentration-dependent contractions of aorta segments with or without PVAT at 37°C. The maximum response, but not pD₂ value, was reduced in aorta segments with PVAT.
3. Cooling the tissues to 24 °C resulted in a significant reduction in the maximum response in aorta segments without PVAT with no change in pD₂ values. However, the anticontractile effect of cooling was attenuated in the presence of PVAT with no significant (p > 0.05) change in either the maximum response or pD₂ value.
4. L-NAME potentiated PE-induced contractions and this was greater in aorta segments without PVAT at both temperatures.
5. The expression of eNOS protein and basal tissue level of nitric oxide (NO) were greater in aorta segments with PVAT at both temperatures. However, PE significantly increased tissue levels of NO only in aorta segments without PVAT.
6. We concluded that PVAT-induced loss of anticontractile effect of cooling against PE-induced contractions could be due to impaired generation of NO in aorta segments with PVAT.