Life and death cell labeling in the microcirculation of the spontaneously hypertensive rat

Spontaneously hypertensive rats (SHRs) have elevated numbers of apoptotic c ells. However, the extent and pattern of cell death at the microvascular le vel is unexplored. We developed a technique to determine early forms of cel l death in vivo in the mesentery by use of the life/death indicator ethidiu m bromide (EB). The mesenteric microvasculature was superfused with 5 muM E B for a period of 3 min, rinsed and immediately viewed by digital fluoresce nce microscopy. EB-positive cell structures were observed both in the wall of microvessels as well as in the tissue parenchyma. The microvessels had a bout 2-4 EB-positive cell structures per 100 mum of vessel length. Larger a rterioles (>25 mum) in the SHR had an increased EB-positive structure densi ty. After normalization of the blood pressure in the SHR with adrenalectomy , no significant differences remained between Wistar-Kyoto (WKY) rats and S HRs. After dexamethasone treatment, the adrenalectomized SHRs had a higher EB-positive cell density in the smaller class of microvessels than the WKY rats. In addition, EB-positive cell fragments (0.5-2 mum) were observed in the mesentery microvessel wall, and with TUNEL labeling, they were demonstr ated to represent DNA fragments. The percentage of microvessels with EB-pos itive fragments was higher in the SHR arterioles and capillaries. Capillari es and larger venules (>30 mum) in the SHR had higher levels of cell fragme nts per vessel length. After adrenalectomy, no significant differences rema ined between WKY rats and SHRs in any of the mcirovessel categories. When a drenalectomized rats were treated with dexamethasone, a higher number of EB -positive fragments was detected in the wall of SHR capillaries. These resu lts indicate that the mesentery microcirculation in both strains is subject to an early and nonuniform pattern of cell death, as detected by EB, but i s enhanced in selected individual microvascular segments of the SHR by a gl ucocorticoid-driven mechanism. Copyright (C) 2001 S. Karger AG, Basel.