The application of cardiopulmonary bypass (CPB) using a heart-lung machine in open heart surgery is associated with numerous pathophysiological changes in the vascular system and the neurohormonal environment. In this study our purpose was to investigate whether the hormones brain natriuretic peptide (BNP) and ghrelin are involved in changes in the systemic vascular resistance index (SVRI) after CPB, using data from 20 patients who had undergone coronary artery bypass grafting accompanied by CPB. Hemodynamic measurements were obtained using a thermodilution catheter and included cardiac index and systemic vascular resistance index. Blood samples were taken before CPB, after CPB, and at 0 and 24 h postoperatively. The blood levels of total and acylated ghrelin were quantified by radioimmunoassay. Blood levels of BNP were measured by a fluorescence immunoassay kit. The SVRI was significantly higher at the end of CPB and at 0 h postoperatively than before CPB (end of CPB: 4282 +/- 1035 dyne x s x cm(-5) x m(-2), 0 h postoperatively: 3239 +/- 635 dyne x s x cm(-5) x m(-2) vs. before CPB: 2289 +/- 330 dyne x s x cm(-5) x m(-2), p < 0.05). Total and acylated ghrelin levels decreased until 0 h postoperatively but the change was not statistically significant. However, at 24 h after surgery, they showed a statistically significant increase over the initial ghrelin values (total before CPB: 1413.71 +/- 287.93 pg/ml vs. 24 h postoperatively: 1736.85 +/- 236.89 pg/ml; acylated ghrelin before CPB: 55.85 +/- 25.53 pg/ml vs. 24 h postoperatively: 106.28 +/- 30.86 pg/ml; p <0.05 for both). BNP values were markedly lower after than before CPB (before CPB: 69.07 +/- 48 pg/ml vs. after CPB: 21.96 +/- 13 pg/ml, p < 0.05) and reached a maximum value 24 h postoperatively (before CPB: 56.3 +/- 42 vs. after CPB: 454.7 +/- 229 pg/ml, p < 0.05). There was a weak negative correlation between the changes in SVRI and total and acylated ghrelin levels after the CPB period, but this was not statistically significant. However, there was a statistically significant negative correlation between SVRI and BNP after CPB and at 24 h postoperatively (r:-0.709, p < 0.01 and r:-0.649, p < 0.03, respectively). Taken together, our results show that the observed initial increases in ghrelin and/or BNP in the postoperative period (at 24 h) might be causally related to the decrease in the SVRI in the same period. However, further investigations are needed to clarify the significance of this observation with respect to that of SVRI.