Calcium channel blocker given intraperitoneally (i.p.) in rats was reported to increase urea D/P ratio without protein loss. Chlorpromazine (CP) given i.p. in humans was reported to increase ultrafiltration (UF) and urea clearance. We studied the effects of i.p. Diltiazem (DZ) (15 mg/kg) and i.p. chlorpromazine (0.25 mg/L dialysate)--given alone or in combination--on urea D/P ratio, dialysate protein (Dpro), glucose concentration (Dg), UF, and drainage volume (Vd). Six male Sprague-Dawley rats were studied. The rats underwent 21 consecutive 30-minute exchanges with 15 mL of 1.5% of Dianeal solution (Baxter Healthcare Inc., Deerfield, Illinois, U.S.A.). DZ or CP was added to the dialysis solution during exchanges 4-6 and 10-12. During exchange 16-18 both DZ and CP were added to the dialysis solution. Exchanges 1-3, 7-9, 13-15, and 19-21 were control exchanges performed with 1.5% Dianeal solution alone. The mean weight of the rats was 541.6 +/- 44 g. The animals' blood pressure remained stable during the study period. An increase in D/Purea ratio was observed with DZ, with CP, and with the two drugs in combination, without increase in dialysate protein loss. An increase in UF with a decrease in D/D0 was observed with DZ, with CP, and with the two drugs in combination, suggesting a mechanism other than osmotic gradient--such as increased blood flow or decreased surface tension.