Increased urinary vasopressin excretion in the DOCA-hypertensive pig

A possible role for vasopressin in the development and/or maintenance of DOCA hypertension in pigs was studied. In control pigs mean arterial blood pressure (MABP), plasma lysine vasopressin (LVP) concentration, the 24-h urinary excretion of LVP (ULVPV) and plasma renin activity (PRA) did not change throughout the 30 days of the experiment. In DOCA-treated pigs MABP began to increase from the initial level of 95 +/- 2 mm Hg within 5 days and reached a level of 127 +/- 3 mm Hg between days 20-30 (P less than 0.01). At this time in the DOCA treated pigs, ULVPV increased threefold (P less than 0.05), although PLVP was unchanged and PRA was reduced to almost zero. After 30 days the pigs were fed a low sodium diet. This was without effect on MABP, PLVP and ULVPV in control pigs. However, in the DOCA-treated pigs, MABP fell from 133 +/- 2 to 112 +/- 6 mm Hg, accompanied by a 60% fall in ULVPV. PLVP was unchanged. Thus in DOCA-treated pigs, LVP appears not to be involved in the development of hypertension, but may be involved in its maintenance.