Serotonin in the control of blood pressure and ultrafiltration in CAPD

Urinary 5-OH-Indoloacetic acid (5-HIAA) indicates the turnover of almost all circulating serotonin (5-HT), a potent vasoactive agent. We tried to investigate the possible excretion of 5-HIAA in the dialysate of CAPD patients and its possible effects on blood pressure control (BP) and/or ultrafiltration (UF). The 24 h excretion of 5-HIAA in the urine of 10 patients with chronic renal failure (CRF) and 8 healthy persons (CONTROL), and in the dialysate of 15 patients on CAPD was measured by FPIA. In CRF 5-HIAA excretion was less than that in control (p less than 0.01). In CAPD patients two distinct patterns of 5-HIAA excretion were found. Patients with high excretion (greater than 6 mg) had high BP and low UF, while those with low excretion (less than 3.14) had low BP, high UF and frequent hypotensive episodes. Excretion of 5-HIAA in the dialysate had a negative correlation with UF (r = -0.779, p less than 0.001) and a positive correlation with B.P. (r = 0.487, n.s.). A highly significant (p less than 0.01) correlation between BP and UF was also found. As no differences between the two groups in factors that could affect UF or BP were found, the implication that 5-HT affects ultrafiltration and/or BP regulation is suggested.