Pituitary factors in blood plasma are necessary for smooth muscle cell proliferation in response to injury in vivo

Insulin glargine reduces carotid intimal hyperplasia after balloon catheter injury in Zucker fatty rats possibly by reduction in oxidative stress

Diabetes and impaired glucose tolerance are associated with increased cardiovascular disease morbidity and mortality particularly after vascular injury. Since insulin is frequently used in such patients, the effect of glulisine (short acting) and glargine (long acting) were tested in Zucker fatty rat carotid artery subjected to balloon catheter injury. Insulin-resistant Zucker fatty rats were sc injected 0.45 mg/kg/d of glargine (once) or glulisine (twice) for 1 week before, and 3 weeks after balloon injury. Fasting and postprandial glucose was measured twice weekly. Injured and uninjured carotid arteries, liver, and aorta were harvested after 3 weeks of injury. Carotid sections were H&E stained for measuring intima/media ratio or immunostained for nitrotyrosine. Serum and aortic protein were analyzed for IGF-1 and 8-isoprostane, respectively. Carotid intima/media ratio was significantly reduced in the glargine group [0.9 +/- 0.1-control; 0.6 +/- 0.1-glulisine; 0.4 +/- 0.1-glargine, P < 0.05]. Serum IGF-1 levels were higher in both insulins, but significant only in glargine group [567 +/- 121 (ng/ml)-control; 1059 +/- 150 (ng/ml)-glargine; P < 0.05]. The aortic 8-isoprostane levels decreased significantly in the glargine group [(921 vs. 2566 pg/mg protein; P < 0.05]. Compared to control nitrotyrosine staining intensity was significantly lower in both groups of insulin-treated rats; the lowest level was in the glargine group. Insulin glargine attenuates carotid intimal hyperplasia in nondiabetic Zucker fatty rat independent of glucose levels and support a valuable function for insulin in vascular disease that merits additional investigations.

The drug-based pipeline against restenosis

More than 1 million percutaneous coronary interventions (PCIs) are performed yearly worldwide. Restenosis is the recurrent narrowing that can occur within 6 months following an initially successful PCI. Although drug-eluting stents have accomplished remarkable success, restenosis has not been eliminated and optimisation of both the polymers and drugs associated with them is desirable. This article reviews the presently available and potential preventive approaches against restenosis, including the sirolimus and paclitaxel drug-eluting stents.

Balloon catheterization induces arterial expression of new Tenascin-C isoform

Migration of smooth muscle cells (SMCs) across the internal elastic lamina is a key step in the development of atherosclerotic or restenotic plaques. Cell movement is a complex and highly dynamic phenomenon, involving the continuous formation and breakage of attachments with the underlying substratum. Tenascin-C (Tn-C), a counter-adhesive extracellular matrix protein, is comprised of several isoforms with distinct biological activities. Neither the structure nor function of these isoforms in SMCs has been defined. We have used primers and RT-PCR to fully identify Tn-C isoforms expressed by SMCs. Cloning and sequence analysis of the PCR product indicated that SMCs express a Tn-C isoform with only repeats A1 and A2 of fibronectin type III repeats. Using A1A2-specific antibodies, cDNA probes and RNase mapping, we observed that the A1A2 isoform is predominantly expressed by cultured SMCs derived from aorta of newborn rats, and its expression is up-regulated by PDGF-BB. In contrast, the expression of this isoform is markedly down-regulated in the SMCs derived from adult rat aorta. Western and Northern blots of injured rat carotid arteries revealed that the A1A2-isoform is expressed in response to injury. Using cultured SMCs, we found that the recombinant A1A2 protein that was found in the newly discovered Tn-C isoform promotes SMC chemotaxis. We conclude that Tn-C isoforms are expressed in a regulated fashion in vascular system. Our findings suggest a new role of Tn-C isoforms in the remodeling of vascular wall.

Social isolation and cardiovascular disease: an atherosclerotic pathway?

This paper outlines two pathways through which social support can influence the prevention or progression of cardiovascular disease: health behaviors and neuroendocrine mechanisms. Its primary focus is on neuroendocrine pathways, reviewing data which suggest that lack of social support is etiologically related to coronary artery lesion development through two mechanisms: sympathetic-adrenomedullary influences on platelet function, heart rate and blood pressure in the initial endothelial injury; and pituitary-adrenal cortical factors involved in smooth muscle cell proliferation during progression of the lesion after injury has taken place. It hypothesizes that the buffering effect of social support on the cardiovascular system is mediated primarily through mechanisms associated with the release of oxytocin.

Enhanced neointimal growth in cultured rabbit aorta following in vivo balloon angioplasty

We have used in vivo balloon catheterization in combination with in vitro organ culture to develop a model system for vascular neointima formation. A Fogarty balloon catheter was used to deendothelialize and rupture the internal elastic lamina of aortae in adult rabbits. After three d of recovery, aortae were harvested, divided into segments, and placed into organ culture. We obtained a daily index of cell proliferation in cultured vessels using [3H]thymidine incorporation into DNA. Also, segments were collected and processed for routine histology or immunohistochemistry. Aortic segments that had undergone ballooning 3 d before harvest and then cultured exhibited diffuse neointimal growth after several d in vitro, whereas those from sham-operated (nonballooned) rabbits showed generally only a single endothelial cell layer that is characteristic of normal intima. Aortae that were harvested, balloon-damaged in vitro, and then cultured exhibited no neointimal growth. The neointima that developed in cultured segments from in vivo ballooned rabbits was primarily of smooth muscle cell origin as determined by positive immunostaining for alpha-smooth muscle actin. The intima:media thickness ratios were significantly higher in aortic segments from ballooned rabbits at harvest and after 4 or 7 d in culture compared with those from nonballooned rabbits. Also, the [3H]thymidine index was higher in the in vivo ballooned aorta compared to non-ballooned or in vitro ballooned vessel. We conclude that ballooning in vivo followed by exposure to blood-borne elements produces an enhanced proliferative response in cultured vessels that is distinct from other in vitro models of neointimal growth.

Angiopeptin inhibits thymidine incorporation by explants of porcine coronary arteries

Angiopeptin, a stable octapeptide analog of somatostatin, inhibits proliferation in a variety of cancer cell lines. We studied the effect of angiopeptin on 3H-thymidine uptake into ring segments from the porcine coronary tree. The incorporation of 3H-thymidine into segments of porcine left anterior descending (LAD) coronary artery was time dependent and reached a plateau after 48 h. The addition of angiopeptin (48.1 and 96.2 nM) to the culture medium significantly inhibited 3H-thymidine incorporation into the segments by 36.7 +/- 10.1% and 48.3 +/- 2.3% of the control, respectively. Forskolin (100 microM), inhibited 3H-thymidine incorporation (52.7 +/- 10.1%) to the same degree as did angiopeptin (96.2 nM). Incubation of the segments with 125I-labeled angiopeptin, for 2 h at 37 degrees C, showed angiopeptin uptake to be time dependent and exhibited a first-order kinetics, reaching equilibrium after 30 min. Autoradiographic studies showed a uniform distribution of angiopeptin within the endothelium, media, and adventitia. Most of the labeling was associated with the nuclei of the cells. Angiopeptin, after 30-min incubation, did not significantly modify the basal levels of cyclic adenosine monophosphate (cAMP). In contrast, forskolin (100 microM) elicited a 50-fold increase of the basal levels of cAMP. These results indicate that in addition to its endocrine effects, angiopeptin reduces the rate of proliferation by acting directly on the vessel wall.

Vasoconstrictor function of the rat isolated perfused mesenteric arterial bed seven days after hypophysectomy

The effect of removal of the pituitary on mesenteric arterial function was examined in adult male rats that had undergone hypophysectomy 7 days earlier. Sham-operated rats and weight-matched rats served as controls. The body weight of hypophysectomized rats decreased from 220.75 +/- 0.48 g to 188.03 +/- 2.53 g (n = 7). Sham-operated controls gained weight, from 223 +/- 1.47 to 275.85 +/- 3.45 g (n = 8). Frequency-dependent vasoconstriction to electrical field stimulation (2-32 Hz, 90 V, 1 ms, 30 s) was significantly augmented after hypophysectomy. The maximal constrictor response of hypophysectomized preparations, 215.5 +/- 14.9 mm Hg (n = 6), was approximately twice that of the sham-operated controls, 100 +/- 6.1 mm Hg (n = 7) and weight-matched controls 109.8 +/- 5.8 mm Hg (n = 8). Norepinephrine (NE) (0.05-1,500 nmol) elicited dose-dependent vasoconstriction; the maximal response was significantly augmented after hypophysectomy, 221.71 +/- 15.9 (n = 7) as compared with 148.0 +/- 16.0 mm Hg (n = 8) in sham-operated controls and 146.3 +/- 8.7 mm Hg (n = 7) in weight-matched controls. Dose-dependent vasoconstrictor responses to ATP, 5-hydroxytryptamine, vasopressin, and endothelin were similar between the groups. High-performance liquid chromatography analysis showed no difference in NE content of the superior mesenteric artery from hypophysectomized and sham-operated controls. Hypophysectomy of rats caused an increase in sympathetic constrictor function of the mesenteric arterial vasculature that appeared to involve postjunctional adrenoceptors rather than prejunctional mechanisms and was not due to arrested growth or the smaller size of the mesenteric preparations.

Estradiol inhibition of arterial neointimal hyperplasia after balloon injury

PURPOSE

Estrogens have been shown to protect against cardiovascular disease in postmenopausal women. The mechanisms are unknown. In this study we investigated the effect of estrogen treatment on arterial neointimal proliferation elicited by balloon injury of blood vessels of the rabbit.

METHODS

The aorta and the common and external iliac arteries of the rabbit underwent balloon injury. 17-beta-Estradiol cypionate (100 micrograms/kg/day intramuscularly) was administered beginning 1 day before injury and until sacrifice at 22 to 24 days after injury. Angiopeptin (20 micrograms/kg/day) was administered for the same length of time as estrogen to a group of rabbits to use this peptide as a positive control for morphometric analysis. Angiopeptin was also combined with estradiol to determine whether it was possible to further enhance the effect of estrogen. Morphometric studies were performed to determine measurement of intimal thickening. Inhibition of cell proliferation by estrogen was evaluated by incorporation of tritiated thymidine in vitro into the balloon injured rabbit aorta 72 hours after balloon injury.

RESULTS

Treatment of male rabbits with estradiol significantly (p < 0.01) decreased the neointimal thickening of these vessels by 50% to 70%. The somatostatin analog, angiopeptin, was similarly effective in the same circumstances. Estradiol failed to further inhibit neointimal thickening when combined with angiopeptin. Treatment with estradiol for 3 days inhibited both thymidine incorporation (p < 0.01) and DNA content in injured vessels.

CONCLUSION

Estradiol treatment of rabbits undergoing balloon injury of the aorta and iliac arteries, significantly inhibits the myointimal thickening. This effect of estrogen is mediated by inhibition of vascular smooth muscle cell proliferation.