The effects of endothelin‐1 and NG‐nitro‐l‐arginine methyl ester on regional haemodynamics in conscious rats with streptozotocin‐induced diabetes mellitus

Resting haemodynamic status and responses to endothelin‐1 (0.004, 0.04, 0.4 nmol kg −1 ) and N G ‐nitro‐ l ‐arginine methyl ester ( l ‐NAME, 10 mg kg −1 ) were assessed in conscious, Wistar rats treated with streptozotocin (STZ) to induce diabetes mellitus, and in control animals treated with saline. In the resting state, STZ‐treated rats had a bradycardia relative to control animals (291 ± 13 and 337 ± 10 beats min −1 , respectively), but mean arterial blood pressures were the same in the two groups (STZ‐treated 109 ± 3; control 114 ± 4 mmHg). However, the STZ‐treated rats had raised renal (105 ± 9 units) and mesenteric (114 ± 16 units) vascular conductances and reduced hindquarters vascular conductance (26 ± 4 units) relative to control rats (renal, 80 ± 6; mesenteric, 75 ± 7; hindquarters, 37 ± 3 units). Increasing doses of endothelin‐1 caused similar, early falls and subsequent rises in mean arterial blood pressures in both groups of rats. Although there were initial hindquarters vasodilatations with endothelin‐1 that were not different in STZ‐treated and control rats, there were subsequent renal and mesenteric vasoconstrictions that were greater in the former. Hence, the similar rises in mean arterial blood pressures must have been accompanied by a greater reduction in cardiac output in the STZ‐treated rats. l ‐NAME caused similar renal and mesenteric vasoconstrictions in control and STZ‐treated rats, but there was a smaller pressor effect and an attenuated hindquarters vasoconstrictor response to l ‐NAME in STZ‐treated rats. Collectively, the results indicate that the resting renal and mesenteric vasodilatations in STZ‐treated rats relative to control were probably not due to diminished vascular sensitivity to endogenous endothelin‐1 or to enhanced sensitivity to, or production of, nitric oxide in these vascular beds. However, the relative hindquarters vasoconstriction in the resting state and the diminished hindquarters vasoconstrictor response to l ‐NAME in STZ‐treated rats is consistent with diminished nitric oxide production in that vascular bed.