Increased proteoglycan synthesis by the cardiovascular system of coarctation hypertensive rats

Effect of calcium channel blockers on proteoglycan synthesis by vascular smooth muscle cells and low density lipoprotein--proteoglycan interaction

Calcium channel blockers are known to retard atherosclerosis. In this study, we tested the hypothesis that one mechanism by which calcium channel blockers retard atherosclerosis is through the modulation of proteoglycan metabolism by vascular smooth muscle cells. We investigated the effect of amlodipine and nifedipine on proteoglycan synthesis by human aortic smooth muscle cells and the ability of the newly synthesized proteoglycans to bind low density lipoprotein (LDL). Confluent smooth muscle cells were incubated with [(35)S]sulfate alone or [(35)S]sulfate and [(3)H]leucine in the presence and absence of different concentrations of amlodipine and nifedipine (0.1--20 microg/ml) for 24 h, and newly synthesized proteoglycans were analyzed. Both amlodipine and nifedipine inhibited proteoglycan synthesis by smooth muscle cells in a dose-dependent manner; however, amlodipine was significantly more potent than nifedipine in this regard. In the presence of 20 microg/ml amlodipine, media and cellular proteoglycans decreased by 56%. This was due to inhibition of de novo proteoglycan synthesis by amlodipine. Compared with the proteoglycans synthesized by control smooth muscle cells, those synthesized by cells exposed to amlodipine were smaller and less sulfated, and contained fewer glycosaminoglycan chains. In addition, proteoglycans synthesized by cells treated with amlodipine bound LDL with low affinity. These results suggest that amlodipine may protect against atherosclerosis through a proteoglycan-mediated mechanism.

Eflornithine alters changes in vascular responsiveness associated with coarctation hypertension

This study examined the temporal effects of the polyamine synthesis inhibitor eflornithine (alpha-difluoromethylornithine) on vascular responses to KCI, norepinephrine, sodium nitroprusside and acetylcholine in aortic rings from coarctation hypertensive rats. Coarctation hypertension reduced the contractile response of aortic rings to KCI and norepinephrine, increased sensitivity (reduced the EC50 value) to norepinephrine and attenuated relaxation to acetylcholine by 14 days of hypertension. Treatment of coarctation hypertensive rats with eflornithine resulted in a normalization of the contractile intensity to KCI and norepinephrine and relaxations to acetylcholine by 14 days of hypertension. Responses to sodium nitroprusside were similar in all groups at all time points. Hyperresponsiveness to norepinephrine produced by coarctation of the aorta was not affected by eflornithine. These studies indicate that normalization of vascular function can occur in the presence of significantly elevated blood pressure upon chronic administration of eflornithine. This functional normalization correlates with eflornithine-mediated regression of structural abnormalities normally associated with pressure overload hypertension.

Multiple polyamine regulatory pathways control compensatory cardiovascular hypertrophy in coarctation hypertension

While a number of factors may initiate structural alterations within the cardiovascular system in response to hypertension, there are obligate cellular signaling mechanisms, such as the polyamines, through which they must operate. This study examined the effects of polyamine synthesis inhibition using eflornithine, a suicide inhibitor of ornithine decarboxylase on blood pressure, compensatory remodeling of the cardiovascular system, and cardiac and aortic polyamine contents using an aortic coarctation model in rats. Eflornithine treatment failed to reduce carotid arterial blood pressure and actually significantly elevated vascular pressure above and below the coarctation site by 14 days of hypertension. Eflornithine only transiently reduced aortic polyamine content of hypertensive rats while this agent reduced coarctation-induced aortic medial wall thickening and the synthesis/deposition of fibronectin and laminin in the hypertensive aorta. Increases in left ventricular mass and polyamine content were concomitantly reduced in hypertensive rats administered eflornithine. These results suggest that multiple polyamine regulatory pathways may maintain vascular polyamine content in response to aortic coarctation; however de novo polyamine synthesis is essential for select aspects of vascular remodeling, including matrix synthesis. Cardiac tissue, in contrast, may rely principally on de novo polyamine synthesis.

Coarctation induces alterations in basement membranes in the cardiovascular system

A coarctation hypertensive rat model was used to examine the effects of elevated blood pressure on basement membrane component synthesis by cardiac myocytes and aorta using immunohistochemistry and Northern blot analysis. Carotid arterial pressure increased immediately on coarctation, and left ventricular hypertrophy was maximal within 5 days. In immunohistochemical studies, fibronectin and laminin were increased and the basement membrane chondroitin sulfate proteoglycan decreased in both the subendothelial space and smooth muscle cell basement membranes of the aorta above the clip compared with controls, whereas only fibronectin was elevated in the aorta below the clip. No change in basement membrane staining intensity for the cardiac myocytes was observed. Alterations in steady-state mRNA levels for fibronectin and laminin in the aorta paralleled those observed by immunohistochemical analysis with regard to protein and tissue type affected as well as intensity of the changes. However, changes in mRNA levels (but not protein deposition) for perlecan and type IV collagen were also observed in aortas from hypertensive rats compared with controls. Increases in steady-state mRNA levels for all basement membrane components in the heart and vasculature peaked before maximal cardiac hypertrophy (5 days). These studies indicate that alterations in basement membrane component deposition in the hypertrophied vasculature occur at both transcriptional and translational levels and suggest that the cell attachment glycoproteins fibronectin and laminin may be important factors in the vascular response to elevated transmural pressure.