Arginine vasopressin (AVP) has been shown to stimulate prostaglandin (PG) production in renal medulla, while PGs have been implicated in the suppression of the antidiuretic activity of AVP. These findings have suggested a local negative feedback system involving PGs in the modulation of the antidiuretic activity of AVP. However, coupling of the antidiuretic activity of AVP to its action to increase medullary PG production is not established. In the present study of rat inner medullary slices, we concurrently examined in the same incubate the relationship between the actions of AVP to increase media immunoreactive PGE (iPGE) and tissue cAMP, the presumed first biochemical step in expression of the antidiuretic activity of the hormone. The synthetic AVP analogue [1, d(CH2)5Tyr(Me)AVP], which selectively blocks the pressor but not the antidiuretic activity of AVP, abolished the action of AVP to increase media iPGE in inner medullary incubates but did not alter AVP induced increases in tissue cAMP in slices from the same incubates. By contrast, the analogue [d(CH2)5Tyr(Et)VAVP], which blocks both the pressor and antidiuretic activity of AVP, inhibited both the cAMP and iPGE responses to AVP. The analogue 1-deamino-8-D-AVP (dD'AVP), which has potent antidiuretic activity but little if any pressor activity, markedly stimulated inner medullary cAMP accumulation without altering media iPGE. These results indicate that the acute actions of AVP to increase inner medullary cAMP and iPGE are separable and independent. The latter effect of AVP appears to be linked to the pressor rather than the antidiuretic activity of the hormone.U