A. J. Pijl

The Effects of Hypertension and Diabetes Mellitus on the Vascular Reactivity of Resistance Arteries

We have studied the effects of both hypertension and streptozotocin-induced diabetes mellitus on alpha 1-adrenoceptor mediated vasoconstriction, endothelium-dependent and endothelium-independent vasodilation. The experiments were performed in perfused mesenteric vascular bed preparations taken from age-matched SHR, WKY, diabetic SHR and diabetic WKY. For the alpha 1-adrenoceptor agonist methoxamine, the mesenteric preparations from SHR and diabetic SHR yielded significantly (p < 0.05) stronger maximal responses than preparations taken from WKY and diabetic WKY, respectively. The diabetic state significantly (p < 0.05) decreased the responsiveness to methoxamine in arteries from SHR and WKY. Hypertension does not significantly change the concentration response-curves for (acetyl-beta) methacholine, histamine, adenosine diphosphate and sodium-nitroprusside. However, the sensitivity to endothelium-dependent vasodilation decreased in preparations from diabetic animals (< 0.05). It is concluded that mesenteric resistance arteries from SHR and diabetic SHR are more reactive to alpha 1-adrenoceptor stimulation, whereas diabetes reduces the responsiveness to methoxamine in WKY and SHR. Hypertension does not affect the endothelium-dependent relaxation in mesenteric arteries. However, diabetes decreases the sensitivity to endothelium-dependent relaxation without altering the sensitivity to sodium-nitroprusside. These findings are indicative of a diabetes-induced endothelial dysfunction in mesenteric resistance arteries. In preparations from diabetic hypertensive rats the reduced response to methoxamine and the endothelial dysfunction seem to run parallel.

Contractile responses to various stimuli in isolated resistance vessels from simultaneously hypertensive and streptozotocin-diabetic rats.

Diabetes mellitus and hypertension are common chronic diseases that frequently occur simultaneously. The induction of streptozotocin (STZ) diabetes mellitus in spontaneously hypertensive rats (SHR) offers the opportunity to investigate the influence of both entities in a reproducible manner. We investigated the effects of various vasoconstrictors on isolated small arteries from the mesenteric vascular bed of normotensive rats (Wistar-Kyoto rats, WKY) and SHR with chronic (8 weeks), STZ-induced diabetes mellitus. No consistent changes in hemodynamic parameters of the (STZ-) normotensive and (STZ-) hypertensive rats were noted. The K(+)-normalization procedure yields the individual optimal lumen diameter, which was the same for the arteries of the four groups of rats. The passive wall tension resulting from this normalization procedure was higher only in preparations from the control hypertensive group as compared with those from the control normotensive rats. Morphological investigations showed that small arteries from control SHR had an increased tunica media thickness as compared with those of control WKY; the STZ-WKY had an increased tunica media thickness as compared with preparations from control WKY. The vasoconstriction caused by alpha 1-adrenoceptor stimulation [norepinephrine (NE), methoxamine] and serotonin is unchanged in chronic experimental diabetes. The diabetic state reduced the sensitivity [-log EC50(M)] for the concentration-response curves (CRC) of calcium chloride. The CRC of potassium chloride indicated the same sensitivities, but maximal active wall tensions of vessels from STZ-SHR were reduced as compared with those from STZ-WKY. The well-known enhancement of the effects of various contractile stimuli caused by hypertension could not be demonstrated for the isolated small arteries used in the present study, although a nonsignificant tendency was observed. However, the STZ-diabetic state did not cause important additional pharmacodynamic changes, despite the morphological alterations in those vessels.

Streptozotocin-induced diabetes mellitus in spontaneously hypertensive rats: A pathophysiological model for the combined effects of eypertension and diabetes

Abstract The present study was undertaken to investigate the combined effects of hypertension and streptozotocin-induced diabetes mellitus in the rat. Accordingly, four groups of rats were studied: Wistar Kyoto rats (WKY), diabetic WKY, spontaneously hypertensive rats (SHR) and diabetic SHR, respectively. The mean arterial blood pressure was increased in hypertensive animals compared to normotensive animals. The base excess in the diabetic rats was higher than that of normoglycemic animals. An elevated glucose concentration was found in the blood and urine of streptozotocin-treated rats. Ketone bodies were detected in the urine and blood of the diabetic rats. Mortality rates after treatment were not different among the four groups. In separate experiments, isolated working hearts of the various groups were set up and analyzed. For the maximal left ventricular pressure (mm Hg) the following values were formed: 110.0 ± 2.6, 93.6 ± 2.7, 93.4 ± 3.0, and 87.5 ± 2.4, respectively. The wet heart weights, dry heart weights, and body weights of the diabetic rats were lower than those of normoglycemic animals. The wet heart weight/body weight ratio, however, was increased by diabetes and hypertension (0.43 ± 0.01, 0.47 ± 0.01, 0.47 ± 0.01, and 0.54 ± 0.02, respectively). There were no significant differences between the water content of the hearts from the four different groups. Pathologic examination of the hearts showed myocardial hypertrophy and medial hypertrophy of coronary arteries in diabetic and hypertensive animals. There was no difference in relative collagen content in the hearts of the four groups. In conclusion, the experimental procedure used appears to be an unique model to study the effects of diabetes and hypertension separated as well as combined.

Cardioprotection by nifedipine in isolated working hearts: a comparative study on three different types of experimental ischemia.

Cardiac ischemia can be provoked by different methods in animal models and in isolated organs. Accordingly, three different procedures were followed to find the most sensitive model for the analysis of the anti-ischemic activity of calcium antagonists. The experiments were performed in the isolated working heart preparation of the rat, paced at the frequency of 5 Hz and perfused with Tyrode solution at 37°C. Global ischemia was achieved by closing off the supply of the perfusion medium and surrounding the heart with Tyrode solution of 37°C gassed with N2; low-flow ischemia was achieved by reducing the cardiac afterload from 51.5 to 11.0 mm Hg; ligation of the left descending coronary artery was performed in order to provoke regional ischemia. Nifedipine was applied in a concentration (EC50) known to reduce the contractile force by one-half of its basal value. The following parameters were determined after 15 min of nifedipine pretreatment and at the end of the experiment: LVP (left ventricular pressure), +dP/dtmax (LVPs first derivative), AO (aortic output), CF (coronary flow), and CO (cardiac output). From the data obtained, the percentages of recovery were calculated. Nifedipine caused a significant improvement in the functional recovery of most of the parameters studied. This improvement, however, was much more pronounced in the model of the low-flow ischemia, which is obviously more sensitive to the anti-ischemic activity of calcium antagonists than the other experimental procedures studied. Low-flow ischemia appears to be preferable to other procedures for the screening of the potential anti-ischemic activity of calcium antagonists and other drugs.

Antiischemic effects of nifedipine in isolated working heart preparations of healthy, diabetic, and hypertensive rats

We evaluated the antiischemic effects of nifedipine in isolated working rat hearts from age-matched normotensive Wistar-Kyoto rats (WKY), diabetic WKY, spontaneously hypertensive rats (SHR), and diabetic SHR. Diabetes was induced by streptozotocin. First, we constructed concentration-response curves for the negative inotropic effect of nifedipine in every group. After 15 min of pretreatment with nifedipine (EC60), low-flow ischemia (30 min) was induced by reducing the afterload from 51.5 to 11.0 mm Hg and nifedipine was infused simultaneously. The six measured parameters were left ventricular pressure (LVP), maximum rate of pressure increase (+dP/dtmax), maximum rate of pressure decrease (-dP/dtmax), aortic output (AO), coronary flow (CF), and cardiac output (CO), determined after 15-min equilibration in the working heart mode and at the end of the experiment. From these data, the recovery percentages were calculated. There were no significant differences in sensitivity to nifedipine (as measured by the EC50 concentration) between the four groups with respect to LVP, +dP/dtmax, -dP/dtmax, CF, and CO. However, hearts from SHR were less sensitive to nifedipine than those from diabetic SHR and nondiabetic WKY with regard to AO. In isolated hearts from nondiabetic WKY and SHR, there were no significant differences between vehicle-treated organs and nifedipine-treated preparations. In hearts from diabetic WKY and diabetic SHR, however, the nifedipine-treated group (LVP 87.1 +/- 3.3 and 60.5 +/- 12.1%, respectively) recovered significantly (p < 0.05) better from ischemia as compared with the control group (LVP 35.7 +/- 14.7 and 10.7 +/- 9.8%, respectively) (n = 6 for each group).(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic and Antiischemic Effects of Nifedipine, Lacidipine, and Nisoldipine in Rat Isolated Working Heart

Summary We compared two newer dihydropyridine-calcium antagonists (lacidipine and nisoldipine) with the classic prototype of this group, nifedipine, in the rat working heart preparation. The hearts were paced at a frequency of 5 Hz and perfused with Tyrodes solution of 37°C. The following five parameters were determined: left ventricular pressure (LVP), maximal rate of pressure increase ( + dP/dtmax), aortic output (AO), coronary blood flow (CBF), and cardiac output (CO). First, dose-response curves were constructed; from these data the EC50 concentration for the three calcium antagonists was calculated. Subsequently, washout from the cardiac tissue for these three compounds was determined. The effects of lacidipine did not diminish during <90-min washout, whereas the effects of nifedipine disappeared completely in 10 min. The effects of nisoldipine, however, disappeared partly in 10 min. In separate experiments, the antiischemic activity of the three calcium antagonists was analyzed, using low-flow ischemia. The calcium antagonists were used in a concentration that produced a 60% reduction in contractile force (EC60). Nifedipine and nisoldipine caused significant improvement in functional recovery. The antiischemic properties of lacidipine could not be shown because of its slow kinetic properties with accumulation in the membrane phase and slow kinetics with the channel. Nisoldipine and lacidipine appear to be more potent calcium antagonists as compared with nifedipine, whereas lacidipine displays a clearly different kinetic pattern in comparison to nifedipine and nisoldipine. In particular, the extremely slow onset and very long duration of action of lacidipine are of interest.

Effects of R 56865 on postischemic ventricular function in isolated rat working heart preparations obtained from healthy, diabetic and hypertensive animals.

The present study was undertaken to evaluate the effects of R 56865 (N-[1-[4-(4-fluorophenoxy)-butyl]-4-piperidinyl-N-methyl-2-benzothiazolamine) (Fig. 1) on postischemic ventricular function, an inhibitor of the Na+/Ca2+ overload, in the working heart preparation of the rat. The hearts were paced at 5 Hz and perfused with Tyrode solution of 37°C at a physiological pH.After 15 min of pretreatment with R 56865, low-flow ischemia (30 min) was induced by reducing the perfusion pressure from 51.5 mmHg to 11.0 mmHg and R 56865 was infused simultaneously. The hemodynamic effects of R 56865 were evaluated in the concentration range [10−8-3·10−6M]. The five parameters measured were: LVP (Left Ventricular Pressure), +dP/dtmax (maximal rate of pressure increase), AO (Aortic Output), CF (Coronary Flow) and CO (Cardiac Output). They were determined in the working heart mode after 15 min of equilibration and at the end of the experiment. From these data the recovery percentages were calculated. The recovery percentages for the LVP, +dP/dtmax, AO, CF and CO for the control hearts (3.3%, 0.0%, 7.9%, 10.4% and 8.5%, respectively) differed significantly from those at 10−7 M (39.6%, 40.8%, 25.0%, 41.8% and 29.9% respectively). The recovery percentage were the highest at 10−6 M (79.6%, 82.1%, 54.7%, 92.7% and 67.2%, respectively). The concentration of 10−7 M was associated with a smaller reduction in LVP (12.9%) than at ·10−6 M (25.7%).In separate experiments the hemodynamic effects of R 56865 were investigated in working hearts taken from age-matched normotensive Wistar Kyoto rats (WKY), diabetic WKY, spontaneously hypertensive rats (SHR) and diabetic SHR. Diabetes was induced by intravenous (i.v.) Streptozotocin (60 mg/kg), administered at 12 weeks of age. The diabetic animals were kept diabetic for 8 weeks. In this stage there was no difference in mortality rate between the 4 groups. In the four groups studied the R 56865 concentration was ·10−6 M, which had been found as optimal in the experiments with preparations from normal Wistar rats. The recovery percentages with R 56865 for the LVP in hearts derived from the WKY, diabetic WKY, SHR and diabetic SHR were: 88.8%, 82.0%, 49.8% and 53.2% respectively. These percentages were significantly different from the data derived from the vehicle treated hearts (14.6%, 35.7%, 3.2%, 10.7%, respectively). Similar differences also hold true for the other parameters. Accordingly, R 56865 also improves postischemic ventricular function significantly under pathologic conditions, where the recovery of the hearts from SHR was improved less than that of WKY.