Alterations of elastin and elastase-like activities in aortae of diabetic rats

The elastin content of the aortic muscle and the elastase-like activity of the extracts of aortic muscle were studied in spontaneously diabetic BB rats and in rats made diabetic by a single bolus i.v. injection of alloxan. In both modes of diabetes, the total alkaline-insoluble aortic elastin content was significantly reduced in diabetic rats compared to that in the corresponding control rats. This reduction in aortic elastin was also accompanied by a consistent increase in the elastase-like activities of the aortic extracts prepared from the same tissues. Such a reciprocal relationship between aortic elastin content and elastase-like activity has previously been reported in rats with malignant hypertension. Since the rats used in this study were not hypertensive, the altered elastin metabolism observed in this work is likely to be a manifestation of diabetic disease and may in part account for the vascular changes associated with diabetes mellitus.

Mechanism of inhibition by alloxan of ATP-driven calcium transport by vascular smooth muscle microsomes

The direct in vitro effects of alloxan on the Ca2+ handling by microsomal membranes isolated from dog mesenteric arteries were investigated. Preincubation of the vascular muscle microsomal membranes with alloxan showed a suppressive effect on both binding of Ca2+ (in the absence of ATP) and ATP-driven Ca2+ transport. Such an inhibition was time dependent, dose dependent, and temperature dependent. ATP-driven Ca2+ transport was much more susceptible to the inhibitory action of alloxan than Ca2+ binding under all experimental conditions examined. Alloxan inhibited ATP-driven Ca2+ transport at a comparable level over the entire period of Ca2+ uptake, but had no significant effect on the efflux of Ca2+ from preloaded microsomal membranes. This suggests that alloxan exerts its inhibitory effect on the ATP-driven Ca2+ transport via its action on the Ca-pump protein rather than the membrane permeability to Ca2+. Catalase and mannitol but not superoxide dismutase partially protected against such as inhibition by alloxan. The possible involvement of H2O2 mediating the inhibitory action of alloxan was further supported by the finding of a similar in vitro inhibitory effect of H2O2 on the ATP-driven Ca2+ transport by the vascular smooth muscle microsomes.

Interactions of saponin with microsomal membranes isolated from vascular smooth muscle

The effects of the plant glycosides extract, saponin, on various biochemical properties of microsomal fractions isolated from dog aortae and mesenteric arteries were investigated. These properties include binding and transport of Ca2+, ouabain-sensitive K+ activated p-nitrophenyl phosphatase (hereafter termed K+-pNPPase) and binding of radiolabelled antagonists to adrenoceptors. We found that saponin inhibited both Ca2+ binding and transport by the vascular muscle microsomes in a dose-dependent manner, but it caused marked enhancement of the K+-pNPPase activity. Saponin only slightly reduced the Bmax, but not the Kd of [125I]-iodocyanopindolol binding to the beta-adrenoceptors of the dog mesenteric artery microsomes. A similar finding on the [3H]-prazosin binding to the alpha 1-adrenoceptor in dog aortic microsomes was also observed. Our findings are consistent with the "skinning" action of saponin on the smooth muscle and provide direct evidence that saponin does not attenuate the recognition properties of the adrenoceptors in the cell membranes.

In vitro inhibition of calcium binding by alloxan and of calcium transport by isolated vascular smooth muscle microsomes

The primary purpose of this study was to investigate the possible direct toxic effect of alloxan on the Ca2+ handling by microsomal membranes isolated from rat mesenteric arteries. It was found that preincubation of the vascular muscle microsomal membranes with alloxan had a suppressive effect on both binding of Ca2+ (in the absence of ATP) and ATP-supported Ca2+ transport. Such an inhibition was time, dose, pH, and temperature dependent. ATP-supported Ca2+ transport was more susceptible to the inhibitory action of alloxan than Ca2+ binding. Unlike alloxan, another commonly used diabetogenic drug, streptozotocin, was not effective in causing such an in vitro inhibition of Ca2+ handling.