In RESULTS, under Protocol 9, the following sentence has been corrected to read as follows: "However, NE did not significantly (P = 0.2400) increase adenosine levels (basal levels of adenosine were 22 � 4 ng/ml; in the presence of 175 nmol/l of NE, adenosine levels were 27 � 5 ng/ml; in the presence of 275 nmol/l of NE, adenosine levels were 30 � 5 ng/ml)."