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We compared the effects of heart rate reduction (HRR) by the hyperpolarization-activated pacemaker current ([I.sub.f]) channel inhibitor ivabradine (MI+Iva) and the [[beta].sub.j]-blocker atenolol (MI+Aten) on ventricular remodeling and perfusion after myocardial infarction (MI) in middle-aged (12 mo) Sprague-Dawley rats. Mean HRR was virtually identical in the two treated groups (19%). Four weeks after coronary artery ligation, maximal myocardial perfusion fell in the MI group but was preserved in infarcted rats treated with either Ira or Aten. However, coronary reserve in the remodeled hearts was preserved only with Iva, since Aten treatment elevated baseline perfusion in response to a higher wall stress. The higher maximal perfusion noted in the two treated groups was not due to arteriogenesis or angiogenesis. Plasma levels of angiotensin (ANG) II and myocardial ANG type 1 ([AT.sub.1]) receptor and transforming growth factor (TGF)-[beta]1 were reduced during the first week of treatment by both Iva and Aten. Moreover, treatment also reduced arteriolar perivascular collagen density. Despite these similar effects of Iva and Aten on vascularity and ANG II, Iva, but not Aten, attenuated the decline in ejection fraction and lowered left ventricular (LV) end-diastolic volume (LVEDV)-to-LV mass ratio, determined by echocardiography. In conclusion, 1) Iva has advantages over Aten in postinfarction therapy that are not due to differential effects of the drugs on heart rate, and 2) age limits growth factor upregulation, angiogenesis, and arteriogenesis in the post-infarcted heart. arterioles; capillaries; ejection fraction; growth factors; angiotensin II

Mechanical stretch, an important growth stimulus, results not only from pulsatile blood flow and diastolic stretch of the ventricles [cyclic stretch (CS)] but also from tissue expansion during growth [constant static stretch (SS)]. We compared growth factor receptor expression and vasculogenic/angiogenic responses of rat coronary microvascular endothelial cells (ECs) by exposing cells to CS (10% elongation at 30 cycles/min) and SS (constant 10% elongation). Both CS and SS increased VEGF receptor (VEGF-R)2 protein levels and the extent of tube formation and branching. Moreover, both CS and SS enhanced VEGF-induced cell proliferation and tube formation, indicating that both types of stretch increase the sensitivity of ECs to VEGF. Blockade of VEGF-R2 prevented the increases in EC proliferation and aggregate tube length. However, CS but not SS enhanced EC Tie-2 protein and migration. CS affected a greater increase in tube length and branch formation than did SS. A unique finding was that SS but not CS increased VEGFR-1 in ECs. Our study is the first to distinguish between the effects of CS and SS on growth factor receptor expression and rat coronary microvascular EC proliferation, migration, and tube formation. In conclusion, EC angiogenic responses to these two types of stretch display both differences and similarities, but both CS and SS are dependent on VEGF-R2 signaling for their vasculogenic/angiogenic effects. cyclic stretch; vascular endothelial growth factor/receptors; tie-2; coronary vasculogenesis/angiogenesis

We tested the hypothesis that chronically reducing the heart rate in infarcted middle-aged rats using ivabradine (IVA) would induce arteriolar growth and attenuate perivascular collagen and, thereby, improve maximal perfusion and coronary reserve in the surviving myocardium. Myocardial infarction (MI) was induced in 12-mo-old male Sprague-Dawley rats, which were then treated with either IVA (10.5 mg x [kg.sup.-1] x [day.sup.-1]; MI + IVA) or placebo (MI) via intraperitoneal osmotic pumps for 4 wk. Four weeks of IVA treatment limited the increase in left ventricular end-diastolic pressure and the decrease in ejection traction but did not affect the size of the infarct, the magnitude of myocyte hypertrophy, or the degree of arteriolar and capillary growth. However, treatment reduced interstitial and periarteriolar collagen in the surviving myocardium of MI + IVA rats. The reduced periarteriolar collagen content was associated with improvement in maximal myocardial perfusion and coronary reserve. Although the rates of proliferation of periarteriolar fibroblasts were similar in the MI and MI + IVA groups, the expression levels of the [AT.sub.1] receptor and transforming growth factor (TGF)-[[beta].sub.1] in the myocardium, as well as the plasma level of the ANG II peptide, were lower in treated rats 14 days after MI. Therefore, our data reveal that improved maximal myocardial perfusion and coronary reserve in MI + IVA rats are most likely the result of reduced periarteriolar collagen rather than enhanced arteriolar growth. myocardial infarction; coronary circulation; coronary vessels; renin-angiotensin system doi:10.1152/ajpheart.00047.2007

Previous studies have not addressed regional differences in adaptive arteriolar growth in the surviving left ventricular (LV) myocardium after infarction in appropriately aged animals, namely middle-aged or older. Accordingly, we examined the adaptive postinfarction growth of arterioles in two distinct regions, i.e., the LV free wall (LVFW) and septum, of middle-aged rats. We induced a myocardial infarction (MI) in 12-too-old rats to analyze 1) protein expression in VEGF/Flt-1/ Flk-1 and angiopoietin (Ang)-1/Ang-2/Tie-2 systems, 2) the arteriolar DNA synthesis, 3) the extent of the arteriolar bed, and 4) the alteration in minimal coronary vascular resistance. In both regions, arteriolar DNA synthesis was activated between days 4 and 7 after MI. Whereas in the LVFW the degree of DNA synthesis declined between days 11 and 14 post-MI, it continued to rise in the septum, and at day 14, the percentage of the arterioles undergoing DNA synthesis was comparable in the LVFW and the septum (9.7 [+ or -] 1.6 and 7 [+ or -] 2.1%, respectively). Arteriolar DNA synthesis was mainly associated with upregulation of Ang-2 and Tie-2 in both LV regions. Although 4 wk after MI the arteriolar beds in the LVFW and the septum expanded to the size of sham-operated rats, this growth did not compensate for the greater minimal coronary vascular resistance in the former. Thus our findings suggest that 1) the dynamics in adaptive arteriolar growth were similar between the two regions, despite a delay in the septum; and 2) the perfusion deficit in post-MI rats cannot be accounted for by inadequate adaptive growth of arterioles. myocardial infarction; arteriolar density; minimal coronary vascular resistance; angiogenic growth factors

Little is known about the vascular and metabolic adaptations that take place in the fetal heart to maintain cardiac function in response to increased load. Chronic fetal anemia has previously been shown to result in increased ventricular mass, increased myocardial vascularization, and increased myocardial expression of hypoxia-inducible factor-1 (HIF-1) and vascular endothelial growth factor (VEGF). We therefore sought to determine whether chronic fetal anemia induces expression of HIF1-regulated angiogenic factors and glycolytic enzymes in the fetal myocardium. Anemia was produced in chronically instrumented fetal sheep by daily isovolemic hemorrhage (80-100 ml) for either 3 (n = 4) or 7 days (n = 11) beginning at 134 days of gestation (term 145 days). Catheterized, nonbled twins served as controls. Isovolemic hemorrhage over 7 days resulted in decreased fetal hematocrit (37 [+ or -] 1 to 20 [+ or -] 1%) and arterial oxygen content (6.5 [+ or -] 0.4 to 2.8 [+ or -] 0.2 ml [O.sub.2]/dl). Myocardial blood flow and vascularization were significantly increased after 7 days of anemia. Myocardial HIF-1 protein expression and VEGF (left ventricular), VEGF receptor-1 (right ventricular), and VEGF receptor-2 (right ventricular, left ventricular) mRNA levels were elevated (P < 0.05) in 7-day anemic compared with control animals. Myocardial expressions of the glycolytic enzymes aldolase, lactate dehydrogenase A, phosphofructokinase (liver), and phosphoglycerol kinase were also significantly elevated after 7 days of anemia. Despite the absence of a significant increase in myocardial HIF-1 protein in 3-day anemic fetuses, expressions of VEGF, VEGF receptor-l, and the glycolytic enzymes were greater in 3-day compared with 7-day anemic animals. These data suggest that HIF-1 likely participates in the fetal myocardial response to anemia by coordinating an increase in gene expressions that promote capillary growth and anaerobic metabolism. However, factors other than HIF-I also appear important in the regulation of these genes. We speculate that the return of mRNA levels of angiogenic and glycolytic enzymes toward control levels in the 7-day anemic fetus is explained by a significantly increased resting myocardial blood flow, resulting from coronary vascular growth and increased coronary conductance, and a return to a state of adequate oxygen and nutrient delivery, obviating the need for enhanced transcription of genes encoding angiogenic and glycolytic enzymes. anemia; fetus; hypertrophy; myocardium; angiogenesis

Adequate growth of coronary vasculature in the remaining left ventricular (LV) myocardium after myocardial infarction (post-MI) is a crucial factor for myocyte survival and performance. We previously demonstrated that post-MI coronary angiogenesis can be stimulated by bradycardia induced with the ATP-sensitive [K.sup.+] channel antagonist alinidine. In this study, we tested the hypothesis that heart rate reduction with [beta]-blockade may also induce coronary growth in the post-MI heart. Transmural MI was induced in 12-mo-old male Sprague-Dawley rats by occlusion of the left anterior descending coronary artery. Bradycardia was induced by administration of the [beta]-adrenoceptor blocker atenolol (AT) via drinking water (30 mg/day). Three groups of rats were compared: 1) control/sham (C/SH), 2) MI, and 3) MI + AT. In the MI + AT rats, heart rate was consistently reduced by 25-28% compared with C/SH rats. At 4 wk after left anterior descending coronary ligation, infarct size was similar in MI and MI + AT rats (67.1 and 61.5%, respectively), whereas a greater ventricular hypertrophy occurred in brady-cardic rats, as indicated by a higher ventricular weight-to-body weight ratio (3.4 [+ or -] 0.1 vs. 2.8 [+ or -] 0.1 mg/g in MI rats). Analysis of LV function revealed a smaller drop in ejection fraction in the MI + AT than in the MI group (~24 vs. ~35%). Furthermore, in MI + AT rats, maximal coronary conductance and coronary perfusion reserve were significantly improved compared with the MI group. The better myocardial perfusion indexes in MI + AT rats were associated with a greater increase in arteriolar length density than in the MI group. Thus chronic reduction of heart rate induced with [beta]-selective blockade promotes growth of coronary arterioles and, thereby, facilitates regional myocardial perfusion in post-MI hearts. myocardial infarction; angiogenesis; coronary circulation; resistance vessels; capillaries

We previously demonstrated that cyclic stretch of cardiac myocytes activates paracrine signaling via vascular endothelial growth factor (VEGF) leading to angiogenesis. The present study tested the hypothesis that cyclic stretch upregulates tyrosine kinase receptors in rat coronary microvascular endothelial cells (RCMEC) and human umbilical vein endothelial cells (HUVEC). VEGF receptor-2 (Flk-1) protein levels increased in HUVEC and RCMEC in a time-dependent manner, but the increase occurred much earlier in RCMEC than in HUVEC. The enhancement of Flk-1 protein level was not inhibited by addition of VEGF neutralizing antibodies, indicating that VEGF is not involved in stretch-induced Flk-1 expression. VEGF receptor-1 (Flt-1) protein and mRNA were not changed by stretch. However, Tie-2 and Tie-1 protein levels increased in RCMEC. Angiopoietin-1 and -2, the ligands for Tie-2, increased in cardiac myocytes subjected to cyclic stretch but were not affected by stretch in endothelial cells (EC). Stretch or incubation of RCMEC with VEGF increased cell proliferation moderately, whereas stretch + VEGF had an additive effect on proliferation. Mechanical stretch induces upregulation of the key tyrosine kinase receptors Flk-1, Tie-2, and Tie-1 in vascular EC, which underlies the increase in sensitivity of EC to growth factors and, therefore, facilitates angiogenesis. These in vitro findings support the concept that stretch of cardiac myocytes and EC plays a key role in coronary angiogenesis. Flk-1; angiopoietin/Tie; angiogenesis

Myocardial infarction (MI) is characterized by ventricular remodeling, hypertrophy of the surviving myocardium, and an insufficient angiogenic response. Thyroxine is a powerful stimulus for myocardial angiogenesis. Male rats that underwent coronary artery ligation and subsequent MI were given 3,5-diiodothyropropionic acid (DITPA; MI+DITPA group) during a 3-wk period. We evaluated ventricular remodeling using echocardiography and histology and myocardial vessel growth using image analysis. Protein expression was assessed using Western blotting and immunohistochemistry. This study tested the hypothesis that the thyroxine analog DITPA facilitates angiogenesis and influences postinfarction remodeling in the surviving hypertrophic myocardium. The increase in the region of akinesis (infarct expansion) was blunted in the MI+DITPA rats compared with the MI group (3 vs. 21%); the treated rats had smaller percent increases in the left ventricular (LV) volume (64 [+ or -] 14 vs. 95 [+ or -] 12) and the LV volume-to-mass ratio (47 [+ or -] 13 vs. 84 [+ or -] 10) as well as a blunted decrease in ejection fraction (-9 [+ or -] 8 vs. -30 [+ or -] 7%). Arteriolar length density was higher after treatment in the largest (>50% of the free wall) infarcts (64 [+ or -] 3 vs. 43 [+ or -] 7). Angiogenic growth factors [vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF)] and the angiopoietin receptor tyrosine kinase with immunoglobulin and epidermal growth factor homology domains (Tie-2) values were elevated during the first week after infarction. DITPA did not cause additional increases in VEGF or Tie-2 values but did induce an increase in bFGF value after 3 days of treatment. This study provides the first evidence for an anatomical basis, i.e., attenuated ventricular remodeling and arteriolar growth, for improved function attributed to DITPA therapy of the infarcted heart. The favorable influences of DITPA on LV remodeling after large infarction are principally due to border zone preservation. diiodothyropropionic acid; angiogencsis; thyroxine analog; angiopoietin

It appears that there are two classes of human circulating endothelial cell (EC) progenitors, CD[34.sup.+] and CD[34.sup.-]CD[14.sup.+] cells. Attention has focused on CD[34.sup.+] cells, yet CD[34.sup.-]CD[14.sup.+] monocytic cells are far more abundant and may represent the most common class of circulating EC progenitor. Little is known about molecular or physiological factors that regulate putative CD[34.sup.-]CD[14.sup.+] EC progenitor function, although factors secreted by other blood and cardiovascular cells to which they are exposed probably affect their behavior. Hypoxia and stretch are two important physiological stimuli known to trigger growth factors in cardiovascular cells and accordingly may modulate EC progenitors. To investigate the impact of these environmental parameters on EC progenitors, EC production in CD[34.sup.-] CD[14.sup.+] cultures was evaluated. Our data indicate that neither stretch nor hypoxia alters EC production by EC progenitors directly but do so indirectly through their effects on cardiovascular cells. Conditioned media (CM) from coronary artery smooth muscle cells inhibit EC production in culture, and this inhibition is stronger if the coronary smooth muscle cells have been subjected to cyclic stretch. In contrast, cardiomyocyte CM increases EC cell number, an effect that is potentiated if the myocytes have been subjected to hypoxia. Significantly, EC progenitor responses to CM are altered by the presence of CD[34.sup.-]CD[14.sup.-] peripheral blood mononuclear cells (PBMCs). Moreover, CD[34.sup.-]CD[14.sup.-] PBMCs attenuate EC progenitor responsiveness to the angiogenic factors basic fibroblast growth factor (FGF-2), vascular endothelial cell growth factor-[A.sub.165], and erythropoietin while inducing EC progenitor death in the presence of transforming growth factor-[[beta].sub.1] in vitro cyclic stretch; hypoxia; erythropoietin; monocyte; conditioned medium

Lamping, Kathryn G., Lance P. Christensen, and Robert J. Tomanek. Estrogen therapy induces collateral and microvascular remodeling. Am J Physiol Heart Circ Physiol 285: H2039-H2044, 2003. First published July 10, 2003; 10.1152/ajpheart.00405.2003.--Estrogen increases proliferation and migration of cultured endothelial cells and perfusion of ischemic hindlimbs of rabbits. We tested the hypothesis that estrogen is angiogenic and arteriogenic in the heart during progressive coronary occlusion. Ovariectomized (OVX) and 17[beta]-estradiol (1 mg * [kg.sup.-1] [wk.sup.-1] im)-treated OVX (OVX-ES) female New Zealand White rabbits were instrumented with an ameroid occluder on a proximal coronary artery. Four weeks after implantation of an ameroid occluder, we measured myocardial perfusion with microspheres at rest and during adenosine-induced maximal vasodilation. The heart was fixed by perfusion at physiological pressure, and capillary angiogenesis and remodeling were assessed by image analysis of tissue sections in collateral-dependent myocardium. Coronary conductance was higher at rest and during maximal vasodilation in collateral-dependent myocardium of OVX-ES than OVX rabbits. Estrogen treatment increased the wall-to-lumen ratio of collateral vessels while it decreased the wall-to-lumen ratio of noncollateral arteries in normal regions. In normal and collateral-dependent myocardium, mean capillary diameter and capillary volume density were greater in OVX-ES rabbits. However, estrogen had no effect on capillary length density in either region of the myocardium. These data suggest that estrogen, induces remodeling of the collateral vasculature and may stimulate growth of the resistance vessels, thereby providing protection during development of a gradual coronary occlusion. collateral circulation; angiogenesis; arteriogenesis; capillaries

Previous studies from our laboratory and those of others have shown thyroxine to be a stimulator of coronary microvascular growth. The present study tested the hypothesis that 3,5-diiodothyropropionic acid (DITPA), a thyroid hormone analog with inotropic but not chronotopic characteristics, is angiogenic in the nonischemic heart. Daily injections (3.75 mg/kg sc) of DITPA to Sprague-Dawley rats affected protein increases in vascular endothelial growth factor [(VEGF).sub.164], [VEGF.sub.188], basic fibroblast growth factor (bFGF) (FGF-2), angiopoietin-1, and Tie-2 during the first few days of treatment. After 3 wk of treatment, arteriolar length density and the relative number of terminal arterioles ( growth factors; angiogenesis; 3,5-diiodothyroproprionic acid; basic fibroblast growth factor; vascular endothelial growth factor

Cardiac growth stimulation in cats was investigated in relation to hemodynamic load and the renin-angiotensin system (RAS). Pharmacological modulation of RAS with losartan and captopril did not change the extent of the hemodynamic overload or the hypertrophic response induced by pulmonary artery-banded cats. Neither RAS activation nor angiotensin II receptor stimulation is an obligatory and necessary component of the signaling pathway that acts as an intermediary coupling load to the hypertrophic response. Load, independent of RAS, can stimulate cardiac growth.

The hypothesis that early vascularization of the embryonic heart is improved after bolus injections of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) into the vitelline vein before the start of myocardial vasculogenesis was investigated. Findings showed that enhancement of bFGF or VEGF before myocardial vascularization increases vascular growth, the effects of these growth factors on vascular volume and numerical density are temporarily dependent, and bFGF affects ventricular modeling aside from its effects on the coronary vasculature.

Sympathetic innervation has no direct effect on the growth of the microvascular system in fetal rat atrial or ventricular tissue grafted into the host rats' anterior eye chamber. The volume percentage of blood vessels, myocytes, extracellular matrix, and other cells in 14- or 35-days-old innervated grafts is similar to that in noninnervated grafts. Sympathetic innervation has no effect on metabolism and perfusion of the graft.

A study of the relationship between thyroid hormones and coronary neovascularization of embryonic rat hearts reveals that embryonic rat hearts that are cultured in oculo are not affected by thyroid hormones and that increased work-related events lead to the thyroid hormone-induced angiogenic effects observed in loaded hearts. Stimulation of hypothyroidism or T4 administration does not influence vascularity or growth of unloaded hearts. Extracellular matrix and volume densities of myocytes and vessels do not exhibit any variations.

A study of the relationship between age and chronic thyroxine (T4)-induced angiogenesis by comparing control and T4-treated rats of different age groups reveals that chronic T4-induced angiogenic effects are not restricted to senescence. The enhancement in heart rate due to T4 is offset by capillary and precapillary growth, enabling a normal myocardial perfusion per unit mass. Capillary proliferation and diameter increase lead to normal capillary volume density in T4-treated rats that have cardiac hypertrophy.

Image analysis and morphometric measurements in the arteriovenous (A-V) shunt in the left and right ventricles of rats show that arteriolar angiogenesis has a linear relationship with the magnitude of volume overload-induced ventricular enlargement and is responsible for 50% of the cardiac hypertrophy. The arteriolar length density is lesser in the left ventricle of the A-V shunt rats while it is the same in the right ventricle of both A-V shunt and control rats. Thus, capillary and arteriolar growth compensate for the overload-induced ventricular enlargement.

Maximal coronary blood flow and reserve in Fischer 344 rats is modulated by factors such as aging and hypertension. The influence of age factor and hypertension on ventricular structure, function and myocardial microvessels is assayed in middle-aged and senescent rats by inducing hypertension in them. The wall-to-lumen ratios of the finest arterioles is enhanced and the capillary numerical density reduces significantly. The wall-to-lumen ratios of small arterioles is proportionate to the age factor in normotensive rats, suggesting that the hypertension in these age groups involves substantial cell loss and endomyocardial fibroses.

The role of age in the initiation of cardiac hypertrophy induced by thyroxine (T4) was studied by exposing prepubescent and senescent rats to T4 for four days. An increase in left ventricular (LV) mass and RNA/LV were observed in both groups within four days. No enhancement of cardiac hypertrophy similar to those seen in hyperthyroid conditions was observed at various LV epinephrine levels. This suggests that cardiac hypertrophy is not induced by norepinephrine nor is it limited to any age group.

Effects of [VEGF.sub.165] and [VEGF.sub.121] on vasculogenesis and angiogensis in cultured embryonic quail hearts. Am J Physiol Heart Circ Physiol 280: H2240-H2247, 2001.--It has been documented that hypoxia enhances coronary vasculogenesis and angiogenesis in cultured embryonic quail hearts via the upregulation of vascular endothelial growth factor (VEGF). In this study, we compared the functions of two VEGF splice variants. Ventricles from 6-day-old embryonic quail hearts were cultured on three-dimensional collagen gels. Recombinant human [VEGF.sub.121] or [VEGF.sub.165] were added to the culture medium for 48 h, and vascular growth was visualized by immunostaining with a quail-specific endothelial cell (EC) marker, QH1. [VEGF.sub.165] enhanced vascular growth in a dose-dependent manner: 5 ng/ml of [VEGF.sub.165] slightly increased the number of ECs, 10 ng/ml of [VEGF.sub.165] increased the incorporation of ECs into tubular structures, and at 20 ng/ml of [VEGF.sub.165] wider tubes were formed. This pattern plateaued at the 50 ng/ml dose. In contrast, [VEGF.sub.121] did not enhance either the number of ECs or tube formation at these or higher dosages. Combined effects of hypoxia and exogenous [VEGF.sub.165] were then compared. Tube formation from the heart explants treated with both hypoxia and 50 ng/ml of [VEGF.sub.165] had a morphology intermediate to those treated with hypoxia or [VEGFsub.165] alone. Immunocytochemistry study revealed EC lumenization under all culture conditions. However, the addition of [VEGF.sub.165] stimulated the coalescence of ECs to form larger vessels. We conclude the following: 1) [VEGF.sub.121] and [VEGF.sub.165] induced by hypoxia have different functions on coronary vascular growth, 2) unknown factors induced by hypoxia can modify the effect of [VEGF.sub.165], and 3) EC lumenization observed in the heart explant culture closely mimics in vivo coronary vasculogenesis. isoforms; explants; hypoxia; QH1; immunocytochemistry; coronary

Mechanisms of coronary angiogenesis in response to stretch: role of VEGF and TGF-[Beta]. Am J Physiol Heart Circ Physiol 280: H909-H917, 2001.--To test the hypotheses that cyclic stretch of 1) cardiac myocytes produces factors that trigger angiogenic events in coronary microvascular endothelial cells (CMEC) and 2) CMEC enhances the expression of growth factors, cardiac myocytes and CMEC were subjected to cyclic stretch in a Flexercell Strain Unit. Vascular endothelial growth factor (VEGF) but not basic fibroblast growth factor mRNA and protein levels increased approximately twofold in myocytes after 1 h of stretch. CMEC DNA synthesis increased approximately twofold when conditioned medium from stretched myocytes or VEGF protein was added, and addition of VEGF neutralizing antibody blocked the increase. CMEC migration and tube formation increased with the addition of conditioned media but were markedly attenuated by VEGF neutralizing antibody. Myocyte tumor growth factor-[Beta] (TGF-[Beta]) increased 2.5-fold after 1 h of stretch, and the addition of TGF-[Beta] neutralizing antibodies inhibited the stretch-induced upregulation of VEGF. Stretch of CMEC increased VEGF mRNA in these cells (determined by Northern blot and RT-PCR) and increased the levels of VEGF protein (determined by ELISA analysis) in the conditioned media. Therefore, cyclic stretch of cardiac myocytes and CMEC appears to be an important primary stimulus for coronary angiogenesis through both paracrine and autocrine VEGF pathways. These data indicate that 1) CMEC DNA synthesis, migration, and tube formation are increased in response to VEGF secreted from stretched cardiac myocytes; 2) VEGF in CMEC subjected to stretch is upregulated and secreted; and 3) TGF-[Beta] signaling may regulate VEGF expression in cardiac myocytes. cardiac myocytes; endothelial cells; basic fibroblast growth factor; cell migration; cell proliferation; vascular endothelial growth factor; tumor growth factor-[Beta]