Calcium antagonists and renal protection. Current status and future perspectives

During the past decade, considerable attention has been focused on the effects of calcium antagonists on renal function. Direct in vivo and in vitro observations in diverse experimental models indicate that calcium antagonists antagonize preglomerular vasoconstriction. Furthermore, calcium antagonists are postulated to have additional properties that contribute to their ability to afford renal protection. These putative mechanisms include the ability to retard renal growth, and possibly to attenuate mesangial entrapment of macromolecules, and to attenuate the mitogenic effects of diverse growth factors. Although the clinical implications of the above-mentioned findings have not been fully delineated, the results of recent clinical trials indicate that calcium antagonists exert salutary effects on renal function in clinical settings characterized by impaired renal hemodynamics, including transplant-associated acute renal insufficiency and, possibly, cyclosporine nephrotoxicity. Evidence has accrued suggesting that calcium antagonists may also be protective against acute radiocontrast-induced nephrotoxicity. Finally, the renal hemodynamic and natriuretic effects of calcium antagonists commend their use as antihypertensive agents in the management of essential hypertension, renovascular hypertension, and transplant-associated hypertension.

Impaired myogenic responsiveness of renal microvessels in Dahl salt-sensitive rats

The mechanisms mediating abnormal renal autoregulation in Dahl salt-sensitive (DS) rats have not been fully defined. In the present study, we assessed myogenic responsiveness of interlobular arteries (ILAs), afferent arterioles (AAs), and efferent arterioles in isolated perfused hydronephrotic Dahl rat kidneys. Dahl rats were divided into four groups according to strain (Dahl salt-resistant [DR] or DS rats) and dietary sodium manipulation (rats fed low or high salt diets). Systolic blood pressure was elevated only in DS rats fed the high salt diet (202 +/- 4 mm Hg, p less than 0.05). Myogenic responses were obtained by stepwise elevation of renal arterial pressure. Vessel diameters were determined by computer-assisted videomicroscopy. Preglomerular microvessels of DS and DR rats responded differently to changes in renal arterial pressure. AAs and ILAs manifested diminished myogenic responsiveness to increasing renal arterial pressure in DS rats compared with DR rats (p less than 0.05). Both AAs and ILAs in DS rats manifested a higher threshold pressure for eliciting myogenic responses and a decrease in maximal pressure-induced vasoconstriction. The sensitivity of the AA myogenic response to nifedipine was enhanced in DS rats compared with DR rats (p less than 0.05). For rats fed the high salt diet, preglomerular vessels exhibited reduced myogenic responsiveness in both strains. In contrast to preglomerular microvessels, efferent arterioles from all four groups of rats failed to exhibit pressure-induced vasoconstriction. Our data suggest that diminished myogenic responsiveness of AAs and ILAs in DS rats contributes to impaired renal autoregulation in this strain.

[Effect of octopamine on arterial pressure and renal function in the normal rat]

Octopamine is a beta hydroxylated phenylethanolamine which accumulates in patients with chronic liver damage. A pathogenic role of octopamine in hemodynamic and systemic alterations of advanced liver failure was investigated in normal awake rats. An infusion of octopamine (220 ug/kg/min) was associated with an increase in mean arterial pressure, urinary volume, urinary Na and K output and their filtration fractions. Glomerular filtration rate and renal plasma flow were not affected. A sudden and marked decrease in mean blood pressure and diuresis was observed after stopping octopamine infusion. Findings during the infusion differ from those observed in the hepatorenal syndrome, although the post infusion period was characterized by hypotension and oliguria. Octopamine behaves as a vasoconstrictor and may interfere with the action of physiologic neurotransmitters.

Diminished acetylcholine-induced vasodilation in renal microvessels of cyclosporine-treated rats

The mechanisms mediating cyclosporin A (CsA)-induced nephrotoxicity have not been established, but damage to endothelial cells by CsA has been proposed as an important factor. In the study presented here, whether endothelial cell function is impaired in the renal vasculature of CsA-treated rats is investigated. The vasodilatory effects of acetylcholine (ACH) on norepinephrine (NE)-induced microvascular constriction in isolated perfused hydronephrotic rat kidneys pretreated with CsA were therefore examined. Hydronephrosis was established to permit direct visualization of renal microvessels. Nephrotoxicity was induced by s.c. injection of CsA (60 mg/kg/day for 5 days). NE (0.3 microM)-induced afferent arteriolar (AA) constriction was exaggerated in CsA rats as compared with that in vehicle (olive oil)-treated control rats. (reduction in diameter of -34 +/- 3 (SE) versus -26 +/- 2%; P less than 0.05). Similarly, efferent arteriolar (EA) constriction by NE in CsA rats exceeded that of controls (-34 +/- 2 versus -22 +/- 3%; P less than 0.01). The vasodilatory responses evoked by ACH were blunted in CsA rats. The AA response to ACH in CsA rats was significantly decreased (P less than 0.005) at ACH concentrations from 1 nM to 1 microM. Similarly, ACH (1 nM to 100 nM) induced less EA vasodilation in CsA rats (P less than 0.025). In control and CsA rats, the addition of nitro-L-arginine abolished AA and EA vasodilation induced by ACH, suggesting that the sustained vasodilatory responses of AA and EA to ACH are mainly dependent on nitric oxide synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Necrobacillosis with pancytopenia

Two young children whose presentation with necrobacillosis caused considerable diagnostic difficulty resulting in referral to an oncology unit are described. In both cases their severe suppurative multisystem illness was complicated by pancytopenia. One had bone marrow infarcts and severe endocarditis in addition to pulmonary involvement and the other had osteitis which resulted in a deformed humerus.

Effects of water immersion on sympathoadrenal and dopa-dopamine systems in humans

Water immersion to the neck increases central blood volume and evokes a marked diuresis and natriuresis. The present study examined simultaneously effects of water immersion on activities of three endogenous systems thought to participate in sodium homeostasis: the sympathetic nervous system, the atrial natriuretic peptide system, and the renal dopa-dopamine system. Hourly urine collections and antecubital venous blood samples were obtained from 10 normal subjects before, during, and after sitting in a water-immersion tank for 3 h; four control subjects were studied while seated without immersion. Urine volume was increased by more than threefold after 1 h of immersion (from 1.2 +/- 0.2 ml/min at baseline to 5.9 +/- 0.7 ml/min, P less than 0.001) and peaked during the second hour. Urinary sodium excretion increased by more than twofold (from 103 +/- 17 mu eq/min at baseline to 196 +/- 36 mu eq/min at 1 h, P less than 0.001) and peaked during the third hour. Plasma levels and urinary excretion of norepinephrine (NE) and epinephrine were suppressed consistently during immersion (P less than 0.05). There was a marked, prompt, and sustained increase in plasma levels of immunoreactive atrial natriuretic factor (irANF) from 6.9 +/- 1.9 pg/ml baseline to 17.3 +/- 4.3 pg/ml at 1 h (P less than 0.001). Urinary excretion of dopa, dopamine, and 3,4-dihydroxyphenylglycol, a neuronal metabolite of NE, changed in a triphasic pattern, with decreased excretion during the first hour of immersion (P less than 0.01), small but consistent increases during the next 2 h, and decreased excretion, to below baseline, during recovery (P less than 0.01 for dopa and dopamine).(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetes mellitus and hypertension

Diabetes mellitus and hypertension are common diseases that coexist at a greater frequency than chance alone would predict. Hypertension in the diabetic individual markedly increases the risk and accelerates the course of cardiac disease, peripheral vascular disease, stroke, retinopathy, and nephropathy. Our understanding of the factors that markedly increase the frequency of hypertension in the diabetic individual remains incomplete. Diabetic nephropathy is an important factor involved in the development of hypertension in diabetics, particularly type I patients. However, the etiology of hypertension in the majority of diabetic patients cannot be explained by underlying renal disease and remains "essential" in nature. The hallmark of hypertension in type I and type II diabetics appears to be increased peripheral vascular resistance. Increased exchangeable sodium may also play a role in the pathogenesis of blood pressure in diabetics. There is increasing evidence that insulin resistance/hyperinsulinemia may play a key role in the pathogenesis of hypertension in both subtle and overt abnormalities of carbohydrate metabolism. Population studies suggest that elevated insulin levels, which often occurs in type II diabetes mellitus, is an independent risk factor for cardiovascular disease. Other cardiovascular risk factors in diabetic individuals include abnormalities of lipid metabolism, platelet function, and clotting factors. The goal of antihypertensive therapy in the patient with coexistent diabetes is to reduce the inordinate cardiovascular risk as well as lowering blood pressure.

Attenuation of endothelin effects by a chloride channel inhibitor, indanyloxyacetic acid

We have recently proposed that the actions of endothelin (ET) are in part mediated by opening of chloride channels (K. Iijima, L. Lin, A. Nasjletti, and M. S. Goligorsky. Am. J. Physiol. 260 (Cell Physiol. 29: C982-C992, 1991). In the present study the ability of a chloride channel inhibitor, an indanyloxyacetic acid (IAA-94), to block ET-induced effects was examined in cultured vascular smooth muscle cells (VSMC) by spectrofluorometry and direct videomicroscopic visualization of the renal microcirculation in isolated perfused hydronephrotic kidneys (IPHK). A fluorescein isothiocyanate (FITC)-labeled IAA-94 analogue showed specific binding to VSMC. IAA-94 (30 microM) neither affected basal cytosolic calcium concentration ([Ca2+]i) in VSMC nor peak response to ET, but it significantly curtailed sustained elevation of [Ca2+]i (half-time recovery was 147 +/- 23 vs. 248 +/- 33 s in control, P less than 0.05). IAA-94 blunted ET-induced membrane depolarization from 24.5 +/- 3.3 to 8.0 +/- 1.8 mV. In IPHK, ET constricted afferent arterioles (AA) by 29 +/- 2% (18.7 +/- 0.8 to 13.2 +/- 0.6 microns, P less than 0.001). Isradipine reversed this ET-induced vasoconstriction. Pretreatment with IAA-94 did not alter AA diameter, but markedly attenuated ET-induced AA constriction (reduction of AA diameters by only 9 +/- 2%, P less than 0.001). The subsequent addition of isradipine (0.1-1 microM) did not further dilate AA. Our data indicate that IAA-94 markedly attenuates AA vasoconstriction elicited by ET and suggest that ET-induced opening of chloride channels, membrane depolarization, and subsequent activation of voltage-dependent calcium channels contribute to the vasoconstrictor mechanisms of this peptide.

Impaired myogenic responsiveness of the afferent arteriole in streptozotocin-induced diabetic rats: role of eicosanoid derangements

Evidence suggests that diabetes is associated with an impairment of renal autoregulation. It has previously been demonstrated that pressure-induced (myogenic) afferent arteriolar vasoconstriction is well preserved in the isolated perfused hydronephrotic kidney. In this study, pressure-induced afferent arteriolar vasoconstriction was examined in kidneys from streptozotocin-induced diabetic rats. Vessel diameters were measured by videomicroscopy as renal arterial pressure was elevated from 80 to 180 mm Hg. In normal kidneys, the afferent arteriole vasoconstricted progressively as renal arterial pressure was increased (-24 +/- 2% decrement in diameter at 180 mm Hg; N = 35; P less than 0.001). In contrast, afferent arterioles of diabetic kidneys exhibited a greatly attenuated response to pressure (i.e., -3 +/- 2% change at 180 mm Hg; N = 60). In vitro treatment with 100 microM ibuprofen completely restored myogenic vasoconstriction (-21 +/- 2% change at 180 mm Hg), but did not alter myogenic responses of control (i.e., nondiabetic) kidneys. The control of hyperglycemia by insulin treatment resulted in a partial preservation of myogenic vasoconstriction (i.e., -11 +/- 3% change at 180 mm Hg), which was further restored by the administration of a low dose (10 microM) of ibuprofen (-21 +/- 1% change at 180 mm Hg). These observations indicate that diabetes is associated with an impaired responsiveness of the afferent arteriole to pressure that is mediated by an alteration in eicosanoid metabolism. This deranged renal microcirculatory response to pressure may represent a functional impairment of the diabetic kidney that may contribute to the progression of diabetic nephropathy.

Calcium antagonists and the kidney: implications for renal protection

During the past decade, attention has focused on the effects of calcium antagonists on renal function. When administered in vitro to the isolated perfused kidney, calcium antagonists exhibit consistent actions permitting characterization of their renal effects. Calcium antagonists do not affect the vasodilated isolated perfused kidney, but they do dramatically alter the response of this preparation to vasoconstrictor agents. Our recent studies using the isolated perfused hydronephrotic rat kidney model, which permits direct visualization of afferent and efferent arterioles, have demonstrated that the preferential augmentation of glomerular filtration rate observed in the isolated perfused kidney is attributable to preferential vasodilatation of preglomerular vessels. Although the clinical implications of such observations have not been fully delineated, the results of recent studies indicate that calcium antagonists exert salutary effects on renal function in patients with impaired renal hemodynamics. Such disorders include radiocontrast-induced nephrotoxicity and transplant-associated acute renal insufficiency. It is apparent, however, that the effects of calcium antagonists on renal blood flow commend their use in the management of essential hypertension.

Dobutamine stress echocardiography: initial experience of a Canadian centre

OBJECTIVE

To investigate the diagnostic accuracy, electrocardiogram and hemodynamic effects and safety of dobutamine stress echocardiography.

SUBJECTS

Sixty-one patients with suspected coronary artery disease. All patients underwent coronary arteriography.

MAIN RESULTS

The sensitivity of dobutamine stress echocardiography in diagnosis of coronary artery disease in the whole group was 91%. In patients with left anterior descending it was 97%; right 85%; circumflex 76%; three vessel 100%; two vessel 95%; single vessel 77%. Specificity, positive predictive value and accuracy of dobutamine stress echocardiography in diagnosis of coronary disease (whole group) was 57, 94 and 87%, respectively. ST depression of more than 1 mm occurred in 11 patients, ST elevation of more than 1 mm in three patients, T wave inversion in one and T normalization in nine. Significant differences of the effects of beta-blockers were noted on the peak effects of dobutamine as follows: heart rate increase of 46 +/- 22 versus 20 +/- 13 beats/min (P less than 0.0001); systolic pressure increase of 4 +/- 26 versus 22 +/- 19 mmHg (P less than 0.01); diastolic pressure decrease of 18 +/- 16 versus 10 +/- 12 mmHg (P less than 0.03) for patients without or with beta-blockers, respectively. Unifocal ventricular premature beats were noted in 10 patients, atrial premature beats in five and ventricular couplets in one. Angina occurred in 11 patients. Atypical chest pain occurred in seven patients, tingling in 11 and nausea in four. Thirty-six patients were totally asymptomatic.

CONCLUSIONS

In this population with high prevalence (85%) of coronary artery disease, dobutamine stress echocardiography had high sensitivity and positive predictive value for coronary disease detection particularly in patients with left anterior descending or three vessel disease. The specificity and accuracy were not as good, but this may reflect the small number of normal patients. Dobutamine was well tolerated and conveniently administered.

Enhanced myogenic responsiveness of renal interlobular arteries in spontaneously hypertensive rats

We recently demonstrated that the interlobular artery (ILA) constricts in response to elevating renal arterial pressure (RAP), suggesting that the ILA contributes to renal autoregulation. In the present study, we examined the segmental myogenic responsiveness of the ILA in kidneys from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). The tapered nature of the ILA allowed us to characterize the regional responsiveness, using the basal diameter to define segments as either proximal (greater than 60 microns), intermediate (40-60 microns), or distal (less than 40 microns). At 80 mm Hg, segmental diameters were similar in WKY and SHR arteries (proximal, 76.0 +/- 3.1 versus 71.6 +/- 3.5 microns; intermediate, 48.2 +/- 1.4 versus 48.1 +/- 1.7 microns; distal, 30.7 +/- 0.9 versus 27.9 +/- 1.3 microns for WKY and SHR, respectively). In both strains, intermediate and distal segments exhibited graded reductions in diameter as RAP was elevated, whereas proximal segments did not. Pressure-induced decrements in the diameters of distal ILA segments were similar in WKY (-24 +/- 2%) and SHR (-20 +/- 2%; p greater than 0.1). The intermediate ILA of SHR exhibited an augmented myogenic responsiveness, constricting at lower RAP levels and exhibiting greater maximal decrements in diameter at 180 mm Hg (i.e., -19 +/- 2% and -12 +/- 2% for SHR and WKY, respectively; p less than 0.05). Nifedipine (1.0 microM) reduced pressure-induced vasoconstriction of intermediate and distal ILA segments by 56 +/- 11% and 79 +/- 7%, respectively, in WKY.(ABSTRACT TRUNCATED AT 250 WORDS)

Breast cancer diagnosis and prognosis in women following augmentation with silicone gel-filled prostheses

62 healthy women were studied mammographically before and after augmentation mammoplasty. Postaugmentation mammograms were done using both the implant compression and implant displacement technique. The amount of visualisable tissue was measured in all films before and after augmentation. We concluded: State-of-the-art film-screen mammography is extremely difficult to obtain in most patients augmented with silicone-gel-filled prostheses. On average, there is a decrease in measurable visualised breast tissue after augmentation mammoplasty with silicone-gel-filled prostheses. The area of mammographically measurable tissue is no different whether smooth or textured implants are used. Textured implants are less likely to form an early capsular contracture and are therefore preferred. However, the cancer-causing potential of polyurethane in humans is currently unknown. Anterior breast tissue is generally seen better with displacement mammography; posterior breast tissue with compression mammography. Better films are generally obtained when the implant is in the subpectoral position rather than subglandular. The more severe the capsular contracture, the poorer the mammogram. In addition 42 previously augmented patients developed breast carcinomas an average of 8.4 years after augmentation with silicone-gel-filled implants; 95% had palpable lesions (only 60% of which could be seen on mammography), 90% had infiltrating carcinomas, 45% had metastases to axillary nodes, and 7 patients have recurred, 5 of whom have died. We concluded: Augmented women who develop breast cancer are similar, in terms of tumour size and nodal positivity, to non-augmented breast cancer patients who present with palpable masses. When compared with non-augmented women whose breast cancers are found with screening mammography, augmented patients with breast cancer present with a higher percentage of invasive lesions and involved axillary lymph nodes, resulting in a poorer prognosis. The 40% false negative rate for mammography in this series is unduly high and alarming. Augmentation mammoplasty with silicone-gel-filled implants should be discouraged in women with a high risk of developing breast cancer.

Calcium antagonists and the kidney

Recently, attention has focused on the effects of calcium antagonists on renal function. When administered in vitro to the isolated perfused kidney, calcium antagonist exhibit consistent actions permitting characterization of their renal effects. Calcium antagonists do not affect the vasodilated isolated perfused kidney, but they do dramatically alter the response of the kidney to vasoconstrictor agents. In the presence of norepinephrine, calcium antagonists markedly augment glomerular filtration rate but produce only a modest improvement in renal perfusion. Utilizing the isolated perfused hydronephrotic rat kidney model that permits direct visualization of afferent and efferent arterioles, we have demonstrated that this preferential augmentation of glomerular filtration rate is primarily attributable to a selective vasodilation of pre-glomerular vessels. Although the clinical implications of such observations are not yet clear, preliminary studies in experimental animal models indicate that calcium antagonists may exert salutary effects on renal function in clinical settings that are characterized by impaired renal hemodynamics. The possible benefits of calcium antagonists in ameliorating the development of renal dysfunction in patients in whom there is increased risk for the development of acute renal insufficiency remain to be evaluated.

Voluntary exercise and experimental mammary cancer

The results of these studies indicate that voluntary activity suppresses the development of chemically and virally induced primary mammary tumors in rats and mice fed high-fat diets. These diets were chosen to mimic the current U.S. fat consumption of approximately 40% of calories as fat. It remains to be seen if activity exerts a similar suppressive effect on animals fed their customary low-fat diet (10% calories as fat). In general, the activity profiles of the female Fischer F-344 and Sprague-Dawley rat and the C3H/o mu j mouse exhibited a similar pattern with an early peak followed by a gradual plateau over time. The effects of activity on body fat composition showed a trend toward a decreased percent of body fat when compared to sedentary animals but a statistically significant decrease was found only in the F-344 female rat. In the DMBA model, carcinogen dose did alter outcome parameters. For example, time to first tumor was extended under low- but not high-DMBA conditions, and, conversely, tumor multiplicity was significantly decreased in the high- but not low-DMBA group. In the NMU model, an inverse association was found between the amount of activity and tumor incidence. A similar association was not found with the DMBA model. The reason for this is uncertain, but further analysis in terms of other parameters such as total tumor number may shed more light on this discrepancy. The suppressive effect of activity on the MMTV-induced mouse mammary tumor is of particular interest since it raises the possibility that activity may exert effects on the process of provirus insertion, and/or oncogene activation--an area of great potential promise in cancer prevention. Activity appeared to enhance the volume and to a lesser degree the number of metastatic foci in the lungs of F-344 retired breeders under high-fat but not medium-fat conditions. In addition, the most active animals in the high-fat group exhibited the greatest volume of metastases. These results, together with those in the NMU model, point to the critical importance of the quantity of voluntary activity an animal engages in and its relation to both primary and secondary cancer prevention. They imply that beyond a certain point of either frequency or intensity, the beneficial effect of exercise may be nullified by competing deleterious effects. The metastases study has also brought to light the importance of dietary fat as a potential intervening variable.(ABSTRACT TRUNCATED AT 400 WORDS)

Reduction of high-risk sexual behavior among heterosexuals undergoing HIV antibody testing: a randomized clinical trial

BACKGROUND

We evaluated the effect of HIV antibody testing on sexual behavior and communication with sexual partners about AIDS risk among heterosexual adults at a clinic for sexually transmitted diseases.

METHODS

We randomized 186 subjects to receive either AIDS education alone (the control group) or AIDS education, an HIV antibody test, and the test results (the intervention group). These subjects were then followed up 8 weeks later.

RESULTS

At follow-up, mean number of sexual partners decreased, but not differently between groups. However, compared with controls, HIV antibody test intervention subjects, all of whom tested negative, questioned their most recent sexual partner more about HIV antibody status (P less than 0.01), worried more about getting AIDS (P less than 0.03), and tended to use a condom more often with their last sexual partner (P = 0.05): 40% of intervention subjects vs 20% of controls used condoms, avoided genital intercourse, or knew their last partner had a negative HIV antibody test (P less than 0.005).

CONCLUSION

HIV antibody testing combined with AIDS education increases concern about HIV and, at least in the short term, may promote safer sexual behaviors. Additional strategies will be necessary if behaviors risky for HIV transmission are to be further reduced.

Right and left ventricular function after cardiac transplantation. Changes during and after rejection

BACKGROUND

Attempts to identify noninvasive markers of ventricular dysfunction accompanying acute rejection have been hampered by a lack of detailed simultaneous hemodynamic data. Therefore, we prospectively performed serial monitoring of detailed left and right heart hemodynamic parameters in cardiac transplant recipients at the time of routine endomyocardial biopsy to better define the physiology of the allograft heart during and after acute rejection.

METHODS AND RESULTS

To better assess the pathophysiology of the rejection process, 18 cardiac transplant patients were prospectively studied by serial right heart micromanometer catheterization and digital image processing at the time of routine endomyocardial biopsy. Eleven patients had 18 episodes of rejection. Studies of baseline (negative biopsy preceding rejection), rejection (acute moderate rejection), and resolved (first negative biopsy after rejection) states were compared. Seven patients who did not experience an episode of rejection served as the control group. Right ventricular minimum and end-diastolic pressures increased from baseline values of 0.9 +/- 3.2 and 6.9 +/- 3.7 mm Hg, respectively, to 3.2 +/- 5.5 and 9.9 +/- 6.6 mm Hg, respectively, with rejection (both variables, p less than 0.05) and remained elevated despite histological resolution of rejection (4.3 +/- 5.5 and 10.0 +/- 7.1 mm Hg, respectively; p less than 0.05 for both variables compared with baseline values). Concurrently, right ventricular end-diastolic volumes (133 +/- 29, 119 +/- 27, and 114 +/- 30 ml; baseline, rejection, and resolved, respectively) and left ventricular end-diastolic volumes (133 +/- 24, 117 +/- 20, and 113 +/- 30 ml; baseline, rejection, and resolved, respectively) significantly decreased during rejection and remained decreased after resolution of rejection (rejection and resolved compared with baseline values, p less than 0.05). Right ventricular chamber stiffness (0.055 +/- 0.035, 0.085 +/- 0.057, and 0.092 +/- 0.076 mm Hg/ml; baseline, rejection, and resolution, respectively; rejection and resolved compared with baseline values, p less than 0.05) increased with rejection and remained elevated after resolution of rejection. Right ventricular peak filling rate also increased from a baseline value of 2.48 +/- 0.45 to 2.76 +/- 0.63 ml end-diastolic volumes per second with rejection (p less than 0.05). Elevation of right ventricular filling pressures, peak filling rate, and chamber stiffness with a concomitant decrease in end-diastolic volume is consistent with a restrictive/constrictive physiology. Mean arterial blood pressure and systemic vascular resistance were elevated after the resolution of rejection (compared with either rejection or baseline values, p less than 0.05) associated with a higher mean daily dose of prednisone (resolved compared with either baseline or rejection values, p less than 0.05). The control group experienced a time-dependent increase in mean and diastolic systemic arterial pressures (both comparisons, p less than 0.05) without detectable diastolic dysfunction.

CONCLUSIONS

Persistence of biventricular diastolic dysfunction may be due to an irreversible effect of rejection, although multifactorial changes in left ventricular afterload occur that may complicate serial assessment of ventricular function.

Calcium antagonists and renal hemodynamics: implications for renal protection

Recently, attention has focussed on the effects of calcium antagonists on renal function. When administered in vitro to the isolated perfused kidney, calcium antagonists exhibit consistent actions permitting characterization of their renal hemodynamic effects. Calcium antagonists do not affect the vascular tone of the vasodilated isolated perfused kidney, but they do dramatically reverse the response of this preparation to vasoconstrictor agents. Studies using the isolated hydronephrotic rat kidney model, which permits direct visualization of afferent and efferent arterioles, have demonstrated that calcium antagonists selectively vasodilate preglomerular vessels. The clinical implications of such observations are still being delineated. Nevertheless, the results of preliminary studies in experimental animal models and in human transplant recipients suggest that calcium antagonists exert salutary effects on renal function in clinical settings characterized by impaired renal hemodynamics. Furthermore, a case can be made that these salutary renal hemodynamic effects of calcium antagonists commend their use in the management of essential hypertension.

Calcium antagonists and renal hemodynamics: implications for renal protection

During the past decade, attention has focused on the effects of calcium antagonists on renal function. When administered in vitro to the isolated perfused kidney, calcium antagonists exhibit consistent actions permitting characterization of their renal effects. Calcium antagonists do not affect the vasodilated isolated perfused kidney, but they do dramatically alter the response of this preparation to vasoconstrictor agents. Our recent studies with the isolated perfused hydronephrotic rat kidney model, which permits visualization of afferent and efferent arterioles, have demonstrated that the augmentation of glomerular filtration rate observed in the isolated perfused kidney is attributable to preferential vasodilation of preglomerular vessels. Although the clinical implications of such observations have not been fully delineated, the results of recent studies indicate that calcium antagonists exert salutary effects on renal function in patients with impaired renal hemodynamics. Such disorders include radiocontrast-induced nephrotoxicity and transplant-associated acute renal insufficiency. It is apparent, however, that the effects of calcium antagonists on renal blood flow commend their use in the management of essential hypertension.