Decreased relaxation of isolated mesenteric resistance vessels from 2-kidney, 1 clip Goldblatt hypertensive rats.

Cumulative contractile responses to norepinephrine (NE), their potentiation with cocaine and their inhibition by diltiazem, cumulative relaxation responses to adenosine and acetylcholine, and contractile responses to 140 mM K+ were studied in isolated mesenteric resistance vessels (ca 175 mu internal diameter) from 2-kidney, 1 clip (2K-1C) Goldblatt hypertensive Wistar rats (2 week duration) and sham-operated controls. No difference in calculated internal diameter, NE sensitivity (before or after inclusion of cocaine in the bath), maximum NE-induced tension, or rate of relaxation after NE washout was found between the two groups. However, the contractile responses to NE in the presence of diltiazem were greater, and acetylcholine and adenosine were less effective in relaxing NE-induced contractions in vessels from 2K-1C Goldblatt hypertensive rats. Depolarization with 140 mM K+ induced equivalent contractions in the two groups and were inhibited to the same extent by 10(-6) M phentolamine, indicating that the contribution of catecholamines released from sympathetic nerve endings by the 140 mM K+ to the K+ induced contraction was equivalent in the two groups. Decreased relaxation of NE-induced contractions reflects a functional alteration in vascular smooth muscle of resistance vessels from 2K-1C rats that may contribute to the development of elevated total peripheral resistance in this model of hypertension.