Allen W. Davidoff

Antihypertensive drug treatment in chronic renal allograft rejection in the rat. Effect on structure and function.

To gain insight into the contribution of immunologic and hemodynamic factors in the progressive demise of structure and function in chronic renal allograft dysfunction, we studied the histological changes, the immunostainable glomerular anionic sites, and glomerular capillary hydrostatic pressures of rat renal allografts with chronic rejection. Recipient animals were left untreated, received 8 weeks of treatment with the immunosuppressive drug cyclosporine, or received antihypertensive drugs consisting of the combination of reserpine, hydralazine and hydrochlorothiazide, the angiotensin-converting enzyme inhibitor cilazapril, or the angiotensin II receptor blocker L-158,809. Grafts in untreated recipients developed chronic interstitial inflammation, as well as vascular and glomerular lesions consistent with chronic rejection. These lesions were associated with immunohistochemical loss of the negatively charged heparan sulfate proteoglycan side chain. All treatment regimens decreased the systemic and glomerular capillary pressures and were associated with no loss of function, decreased proteinuria, and a tendency to improved graft function. Cyclosporine prevented all histological manifestations of rejection, and antihypertensive drugs decreased the extent of glomerular mesangiolysis and glomerulosclerosis; L-158,809 and cilazapril also inhibited graft atherosclerosis and tubular atrophy. We conclude that chronic rejection is primarily an immune-mediated process, but hemodynamic and angiotensin II-mediated effects may play a pivotal role in the expression of immune-mediated lesions.

Cardiac allograft atherosclerosis in the rat. The effect of histocompatibility factors, cyclosporine, and an angiotensin-converting enzyme inhibitor.

Cardiac transplant atherosclerosis is thought to result from immune-mediated vessel wall injury. The present experiments were designed to test whether CsA alone or in combination with the ACE-inhibitor cilazapril has any effect on graft atherosclerosis in a rat cardiac transplant model. Cardiac grafts were transplanted heterotopically into either syngeneic or allogeneic recipients and followed by daily palpation; long-surviving grafts were removed after 100 days and the extent and degree of atherosclerosis was assessed using computerized morphometry. Atherosclerosis was more extensive in grafts removed from untreated allogeneic recipients compared with syngeneic recipients; CsA treatment increased the extent of atherosclerosis in syngeneic transplants. The extent and degree of vascular occlusion in allogeneic grafts from recipients treated with 15 mg/kg of CsA every other day was not different from that in grafts removed from recipients that received initially higher CsA doses. Cilazapril had no effect on the extent of graft atherosclerosis but decreased the degree of luminal narrowing in grafts from CsA-treated recipients significantly. Some grafts showed neovascularization in the subendocardial region adjacent to organized intraventricular clots, suggesting the release of angiogenic factors from such clots; such growth factors may contribute to the atherosclerotic vessel wall reaction in this model. We conclude that CsA promotes the development of graft atherosclerosis in heterotopically transplanted syngeneic cardiac grafts in the rat. We furthermore found that cilazapril has a beneficial effect on the degree of atherosclerosis in CsA-treated recipients.

Glomerular capillary pressures in long-surviving rat renal allografts.

Many renal transplants undergo gradual deterioration in structure and function in the months or years after transplantation. The processes that underlie this progressive decline have not been defined, and may include immunological and nonimmunological mechanisms. The present experiments were designed to investigate the glomerular capillary hydrostatic pressure in long-surviving rat renal transplants with or without chronic rejection. Stop-flow glomerular pressures were measured in F344 renal allografts with chronic rejection, syngeneic F344 grafts, and long-surviving syngeneic and allogeneic LEW grafts without chronic rejection; control measurements were done in nontransplanted intact animals or after subtotal renal ablation. Renal ablation or transplantation resulted in increased glomerular pressure in F344 but not LEW kidneys; the glomerular pressure in syngeneic F344 grafts was not different

Congestive Heart Failure after Myocardial Infarction in the Rat: Cardiac Force and Spontaneous Sarcomere Activity

Abstract: The causes of reduced cardiac force development in congestive heart failure (CHF) are still uncertain. We explored the subcellular mechanisms leading to decreased force development in trabeculae from rats with a myocardial infarction. We defined CHF according to clinical and pathological criteria and compared properties of trabeculae from animals with CHF (cMI) to those of animals with a myocardial scar but without evidence of CHF (uMI), and sham‐operated animals. The new findings of this study on properties of cMI trabeculae are that (1) maximal twitch force following post‐extrasystolic potentiation is unchanged; (2) the sensitivity of cMI trabeculae to [Ca2+]o is increased; (3) spontaneous diastolic sarcomere length (SL) fluctuations (SA) are increased in cMI at all levels of SR Ca2+ loading; and (4) SA is accompanied by a proportional reduction of Fmax. The results suggest that the probability of spontaneous diastolic opening of SR Ca2+ channels is increased in CHF. These data provide the basis for a novel mechanism underlying systolic and diastolic dysfunction as well as arrhythmias in hearts in CHF. If SA proves to be a component of myocardial dysfunction in human CHF, our thinking about therapy of the patient with CHF may be profoundly changed.

Anti-integrin (LFA-1, VLA-4, and Mac-1) antibody treatment and acute cardiac graft rejection in the rat.

Cell adhesion molecules mediate interactions with other cells and extracellular matrix, control cell infiltration in sites of inflammation, and regulate cell activation. Previous studies have shown that treatment of rat cardiac transplant recipients with a combination of antibodies against the T-cell integrins LFA-1 and VLA-4 gave a modest prolongation of graft survival. Current experiments were designed to examine the effect of blocking Mac-1, an important monocyte adhesion receptor and mediator of monocyte migration, together with anti-LFA-1 and anti-VLA-4 antibodies on cardiac graft survival and on the graft rejection pattern. The anti-Mac-1, CD11b-specific antibody OX-42 did not affect graft survival time although it did decrease the graft infiltration by rounded, ED-2-positive macrophages.

Xenoantibodies in the rat against guinea pig tissues

Abstract. The role of naturally occurring antibodies in discordant xenograft rejection is poorly defined. This is partly attributable to a lack of information regarding their tissue specificity and titers. Sera from different rat strains were studied for naturally occurring antibodies against guinea pig tissues using immunofluorescence and immunoperoxydase staining techniques. All sera contained IgG and IgM antibodies in low titers against erythrocytes. lymphoid cells, and a variety of tissue structures. Intentional immunizations of adult rats with guinea pig cells resulted in the production of xenoantibody specificities that were not detectable in nonimmunized animals. Immunizations of Munich‐Wistar rats with guinea pig skin grafts occasionally resulted in the formation of antibodies that reacted with allogeneic and syngeneic cells of the liver, lung, and lymphoid organs. We conclude that rats have low titers of naturally occurring xenoantibodies against various tissue structures of the guinea pig, but their importance in xenograft rejection remains to be established.

Losartan inhibits myosin isoform shift after myocardial infarction in rats

Hypertrophy and heart failure following a myocardial infarction in rodents are accompanied by a switch of myosin isoforms from V1 to V3. The angiotensin II receptor blocker, Losartan, has been demonstrated to improve cardiac function and long-term survival after myocardial infarction. In this study we have investigated whether chronic Losartan treatment affects myosin isoform composition in the hearts of rats following a myocardial infarction. Rats were subjected to coronary artery ligation and received either Losartan (1 g/L) in the drinking water or water only. Four months after myocardial infarction, rats were classified as having either congestive heart failure (cMI) or uncomplicated myocardial infarction (uMI) based on their lung weight to body weight ratio (LW/BW). Compared with sham operated rats, uMI rats showed a 68.5% increase in the relative contribution of V3 and a 33.7% decrease in the relative contribution of V1 (p < 0.05). Untreated cMI showed 39.7% more V3 and 38.2% less V1 when compared with untreated uMI (p < 0.05). Losartan treatment after myocardial infarction reduced the incidence of cMI from 30.4 to 4.5% and scar size from 1.52 ± 0.07 to 0.94 ± 0.11 cm2 respectively. The percentage of V1 in Losartan treated uMI (LuMI) was 25.2% higher than the percentage of V1 in untreated uMI (p < 0.05), whereas the percentage of V3 in LuMI was 24.2% lower than that in untreated uMI (p < 0.05). A positive correlation of V3 myosin and scar area was observed. Our study suggests that expression of V3 myosin in the left ventricle is associated with scar size and the progress of hemodynamic changes after myocardial infarction. Losartan treatment reduces scar size and wall stress of the heart after the infarct, and therefore inhibits the signals shifting myosin isoform expression from V1 to V3 after a myocardial infarction.