Direct tubular effects of prostaglandins (PG's) on Na transport were examined in isolated cortical and medullary collecting tubules of rabbits perfused in vitro. The animals were treated with deoxycorticosterone acetate (DOCA, 1 mg kg-1 day-1, i.m.) for 3-6 days before experiments. In the cortical collecting tubules PGE2 (1.2 X 10(-7)-2.5 X 10(-5) M), E1 (1.2 x 10(-5) M) and F2alpha (1.2 x 10(-5) M) added to the bath caused reversible decreases in transtubular potential difference (PDt). But neither PGE2 (1.2 X 10(-5) M) added to the perfusate nor PGA2 (1.2 X 10(-5) M) added to the bath had an effect on PDt. The net Na absorption was decreased with PGE2 (1.2 X 10(-5) M) added to the bath from 8.6 +/- 1.36 to 1.5 +/- 1.04 pEq cm-1 s-1 (P is less than 0.02). In rabbits not pretreated with DOCA, the net Na absorption was reduced from 2.73 +/- 0.74 to 1.02 +/- 0.74 pEq cm-1 s-1 (P is less than 0.01). In the outer medullary collecting tubules PGE2 (1.2 X 10(-5) M) added to the bath also caused a reversible decrease in PDt. It is concluded that PGE2, F2alpha and E1 inhibit Na absorption in the collecting tubules by acting on the peritubular membrane.