The cellular biology of angiotensin: Paracrine, autocrine and intracrine actions in cardiovascular tissues

J Mol Cell Cardio121, (Supplement V), 63-69 (1989)

The

Cellular Biology of Angiotensin: Paracrine, Intracrine Actions in Cardiovascular Richard

Alton Ochsner Medical

Foundation,

Autocrine Tissues

and

N. Re

1516 Jefferson Highway,

.hfew Orleans, LA 70121, USA

R. N. RE. The Cellular Biology of Angiotensin: Paracrine, Autocrineand Intracrine Actions in Cardiovascular Tissues. 3oumal of A4olecular and Cellular Cardiology (1989) 21, (Suppl V), 6349. A growing body of evidence suggests that angiotensin II, the effector protein of the renin-angiotensin system, is intimateiy involved with cell growth in target tissues. Most recently, evidence has been provided to indicate that angiotensin II is capable of inducing a hypertrophic response in cultured arterial smooth muscle cells. At the same time, considerable evidence has been developed to indicate that local analogs of the systemic renin-angiotensin system exist in multiple tissues and, in particular, in the vascular wall and the heart. Finally, data have accumulated to indicate that local growth regulatory factors, in many instances operating through regulation of proto-oncogene transcription, are involved in the hypertrophic and hyperplastic sequelae of hypertension, Included amongst these growth factors is angiotensin II. Thus, accumulating data indicate that angiotensin II is a growth factor with potential implications for the development of the sequelae of hypertension. In addition, studies from this laboratory and others suggest that angiotensin acts at least partially through what we have called an “intracrine” mechanism to produce its effects. In these multiple actions, angiotensin may provide a paradigm for other peptide growth factors and hormones. KEY WORDS: Angiotensin

II; Growth

factors;

Proto-oncogenes;

Introduction

The renin-angiotensin system is wellestablishedas a major factor in the maintenance of cardiovascular homeostasis.More recently, it has been demonstrated that tissue renin-angiotensin systems exist, and it has been suggestedthat thesesystemsplay important roles in local tissue physiology. It is here argued that the reinin-angiotensin systems present in the vasculature and heart are important determinants of cardiovascular function (e.g. arterial resistance) and structure (e.g. vascular hypertrophy). Moreover, it appears that these local renin systemsrepresent but a part of a larger growth regulatory or “cytokine”-like network important in the regulation of hypertrophy and hyperplasia in the cardiovascular system. Finally, evidence pointing to a possible intracellular site of angiotensin II action will be discussedand the possibility that other peptide hormones and peptide growth factors operate in a similar fashion will be considered. 0022-2828/89/055063

+ 07 $03.00/O

Intracrines

The

renin-angiotensin system regulator of cell growth

as a

In the 197Os,the studies of Khairallah et al. (1972) suggestedthat angiotensin II was capable of stimulating DNA, RNA, and protein synthesis in isolated cardiac tissue. At the same time, these workers suggested that angiotensin II was capable of gaining accessto cellular interiors and of localizing to nuclei and mitochondria. More recently, a potential influence of angiotensin II on the mitogenic activity of 3T3 cellsaswell ascultured adrenal cells has been reported and, within the last year, evidence has indicated that angiotensin II is capable of inducing a hypertrophic responsein cultured arterial smooth muscle cells (Ganten et al., 1975; Simonean and Gill, 1979: Re, 1984, 1987c; Owens, 1987; Taubman et al., 1987; Kawahara et al., 1988; Owens et al.. 1988; Geisterfer, 1988). This hypertrophyproducing effect in cultured arterial smooth musclecellsis associatedwith accummation of c-fos mRNA (Taubman et al., 1987; Kawah@) 1989 Academic

Press Limited

R. N. Re

64

ara et al., 1988). Moreover, Dzau and colleagues have demonstrated that continued exposure of such cultured cells to angiotensin II results in the accumulation of PDGF-A mRNA (Nastilan et al., 1988). The possibility that locally-produced PDGF-A could play a role in the hypertrophic response is intriguing. In any case, persuasive evidence has been marshalled to indicate that angiotensin II in appropriate circumstances can function as a trophic hormone, just as other growth factors can, in certain circumstances, demonstrate vasoactive properties (Kawahara et al., 1988; Sporn and Roberts, 1988). Local

renin-angiotensin

systems

Over the last 10 years or so, components of the renin-angiotensin system have been conclusively identified in multiple tissues and, in many of these, synthesis has similarly been proven (Celio and Inagami, 1981; Dzau and Re, 1987; Re, 1987b, c; Re et al., 1982). Our laboratory has been interested in the local synthesis of components of the reninangiotensin system in cardiovascular tissue (Dzau and Re, 1987; Re, 1987; Re et al., 1982). We and our colleagues demonstrated the presence of antibody inhibitable enzymatic renin activity in cultured canine arterial smooth muscle cells. In addition, we used specific anti-renin antibodies to demonstrate cytoplasmic localization of reninthe containing granules in these cells, and biosynthetic labeling studies were carried out to demonstrate the synthesis of renin. In more recent studies, we have detected antibody inhibitable renin activity in short-term cultures of rat cardiac myocytes, and mRNA for renin has been detected in cardiac myocyte preparations as well (Dzau and Re, 1987). Although it is not possible to totally exclude contamination of these preparations by nonmyocyte cardiac cells, quantitative arguments make this relatively unlikely. More recently, we have detected the presence of angiotensin II in these cell preparations suggesting the presence of an intact renin-angiotensin system in the myocardium (Re, 1987; Re and MacPhee, 1987). Others have simiIarly detected the components of the renin-angiotensin system in intact hearts uin et al., 1988). These observations, taken to-

gether with the growing evidence suggesting growth regulating effects of angiotensin II. raise the possibility that local as well as systemic angiotensin II could play a role in the development of the sequelae of hypertension as well as in the local regulation of vascular resistance (Re, 1987c; Dzau, 1988). In particular, they raise the possibility that angiotensin II could directly play a role in vascular cell hypertrophy and, perhaps, in cardiac myocyte hyptertrophy in hypertension. The wellestablished effects of converting-enzyme inhibitors, calcium channel blockers, and even certain centrally active adrenergic inhibitors are consistent with this hypothesis (Pfeffer et al., 1982; Dunn et al., 1984; Fouad-Tarazi and Leibson, 1987; Orekhov, 1987; Re RN, 1982a; Weiss, 1987). In addition, it is possible that angiotensin II in the heart could alter catecholamine release with secondary effects on hypertrophy. In this regard, it is of interest to note that in the 1970s considerable investigation centered on the question of whether or not the high renin state was associated with excessive morbidity and mortality as a result of the secondary generation of elevated angiotensin II plasma concentrations (Brunner et al., 1972; Kaplan, 1973). Given the recent evidence suggesting an effect of angiotensin II on vascular cell growth as well as on cardiac remodeling, our group investigated this issue utilizing echocardiography. Interestingly, we found that posterior wall thickness and relative wall thickness correlated with circulating angiotensin concentrations (Schmieder et al., 1988). This evidence further suggests that angiotensin II may, in certain circumstances, play a physiologically relevant role in determining cardiovascular structural states and also indirectly suggests that local angiotensin II generation could be important in the generation of the sequelae of hypertension. Local growth factors in the cardiovascular system Evidence is accumulating to suggest that a variety of factors in addition to angiotensin II can operate in the cardiovascular system to regulate growth and development. Serotonin, interleukin I, platelet derived growth

Angiotensin encephalin and. a factor(s), vasopressin, variety of others have all been demonstrated in one circumstance or another to influence vascular cell growth (Dzau and Gibbons, 1987). In addition, a wide variety of factors have been demonstrated to be growth promoting or inhibiting depending on the ambient tissue milieu (Sporn and Roberts, 1988). For example, transforming growth factor /I has been demonstrated to induce the synthesis and secretion of PDGF and other growth factors from endothelial cells, while under other circumstances it directly inhibits the mitogenic activity of arterial smooth muscle cells (Nicholson et al., 1987; Sporn and Roberts, 1988;l. Starksen et al. (1986) have demonstrated that the hypertrophic response which is seen in cultured cardiac myocytes upon the administration of c+adrenergic agonists is associated with the accumulation of c-myc message. Our group has demonstrated that dispersed cells derived from the hearts of SHR animals contain elevated c-,myc and c-sis message as contrasted with WKY animals (Rovigatti and Re, 1987). Moreover, the study of long-term cultures of non-myocyte cardiac cells reveals the same differences. This elevation of c-sir is consistent with the vascular hyperplasia which has been documented in the resistance vessels of thr SHR rat (Owens et al., 1988). Presumably the vascular cell hypertrophy which is seen in the larger vessels of the animal could be related to angiotensin II or other factors (Owens, 1987). Barrett and co-workers have demonstrated the presence of PDGF-like material in various cells comprising the normal arterial wall, and it remains unclear if this message is translated and what its effects might be on nearby cells (Barrett and Benditt, 1987a,b). Since proliferation is not seen in the normal resting arterial wall, one could hypothesize the absence of translation of the PDGF message, the rapid breakdown of any synthesized product, the co-secretion of growth-inhibiting factors, the absence of appropriate concentrations of other necessary growth factors, or the absence of receptors on nearby cells for the specific dimeric form of PDGF which is secreted. In this regard, it recently has been demonstrated that cells may differ in their response to PDGF AA and PDGF AB (Nister et al., 1988; Rich-

Biology

65

at&m et al., 1988). Of note, however, is the observation that the atherosclerotic plaque appears to contain elevated levels of PDGF, as well as a transforming oncogene or “atherogene,” suggesting that the atherosclerotic plaque may, lat least in part, develop because chronic stimulation, viral infection, mutagenic agents, or genetic instability produces persistent or abnormal prroto-oncogene activation (Penn et al., 1986; Barrett and Benditt. 1987a,b; Majesky et al., 1987). In sum, there appears to be a wide variety of growth factors whose actions are associated with proto-oncogene transcription and whose effects influence cardiovascular structure both in health and disease. The renin-angiotensin system in its systemic and local forms appears to be one such factor. The intracrine

angiotensin

II system

The original work of Khairallah et al. i 1972, suggested that angiotensin II was capable of gaining access to cell interiors and binding to a nuclear material. Our group elected to confirm these observations by studying isolated nuclei derived from spleen or liver (Re and Bryan, 1984; Re et al., 1981, 1984a,b). In these preparations, we detected the presence of high affinity, specific angiotensin II receptors. In that additional studies, we demonstrated exposure of tissues or nuclei to angiotensin II produced conformational changes in chromatin which could be unmasked by digestion with either micrococcal nuclease or DNase 1 (Re et al., 1984a). These data indicated that the binding of angiotensin II to its nuclear receptors produced changes in chromatin conformation similar to those seen during gene transcription. Of note was the fact that the treatment of nuclei with angiotensin II, followed by brief enzyme digestion, revealed the presence of specific chromatin angiotensin I1 receptors in the solubilized chromatin. whereas digestion in the absence of angiotensin II failed to generate moieties demonstrating specific binding. These data were interpreted as indicating that angiotensin II binding to receptors increased the solubilization of‘ those receptors by micrococcal nuclease and DNase I - again suggesting that binding of the hormone to its chromatin receptors produced a conformational change similar to that ex-

66

R. N. Re

petted during the transcription of nearby genes. In additional studies, an attempt was made to isolate this chromatin receptor, and a specific species was identified on DNP gels which migrated slightly more rapidly than nucleosomal DNA (Re et al., 1984a). Additional efforts are underway to purify this species which appears to be a protein tightly bound to chromatin. In an additional series of experiments, angiotensin II was demonstrated to increase RNA synthesis by isolated nuclei (Re and Parab, 1984). Alpha-amanitin inhibition studies revealed that the majority of this enhanced RNA polymerase activity was the result of stimulation of RNA polymerase II. This raises the possibility that message-related RNA polymerase II activity is stimulated by intracellular angiotensin. The mechanism(s) by which this occurs is yet unknown. Finally, data were generated to indicate that angiotensin II increases the solubilization of copper from chromatin (Bryan et al., 1985). These data suggest the possibility that copper is intimately related to angiotensin II-induced initiation sites and perhaps is involved either with the angiotensin II receptor or with the initiation complex. Further work in this area is underway.

FIGURE fragments) the binding cytoplasmic

Based on these studies, we suggested that peptide hormones, in certain circumstances, were capable of acting in what we deemed an intracrine mode (Re and Bryan, 1984; Re el al., 1984b). By this we meant peptide hormones which were capable of operating within their cells of synthesis. Presumably, such intracrine effects could be manifested after secretion and reuptake of the hormone or without the intermediate of secretion (Fig. 1). Recently, it has been demonstrated that, in cells transformed with the $2~ oncogene, PDGF need not be secreted into the extracellular medium but may activate receptors intracellularly, presumably receptors within the Golgi compartment (Williams, 1988). This, in our view, constitutes an intracrine effect. Even more interesting, however, is the recent report that the growth factors PDGF, epidermal growth factor (EGF), and nerve growth factor (NGF) bind specifically to chromatin with high affinity when either intact cells or isolated chromatin is exposed to the growth factors (Rakowicz-Szulzynskce et al., 1986). In addition, this chromatin binding can be blocked by specific monoclonal antibodies directed against the appropriate growth factor receptor. Finally, each of these growth factors produced a resistance in chromatin to DNase II

1. Intracrine effects could be generated by: (I) translocation of hormone (H) (or hormone/receptor from the cell surface to chromatin with or without the intra-lysosmal generation of peptide fragments, (2) of newly synthesized hormone to intracellular receptors with the generation of second messengers, or (3) the synthesis of hormone followed by binding to chromatin.

Angiotensin

in the regions to which they bind. All these findings are analogousto those we have previously reported for angiotensin II and suggest that all these factors interact with chromatin receptors and, thereby, produce conformational changes like those seen with the enhancement or suppressionof transcriptional activity (Re and Bryan, 1984; Re et al., 1984a,b). Also of interest is the recent report that basic fibroblast growth factor (bFGF) is capable of entering cells and translocating to nucleoli whereupon it stimulates RNA polymerase I activity and specific transcription of ribosomal genes (Bouche et al., 1987). These findings again parallel those which we have reported for angiotensin II (Re and Parab, 1984). Yet another similarity between these recent findings and those we have reported is the fact that the chromatin receptors for NGF, PDGF, and EGF, like our angiotensin II receptor, are extremely tightly bound to chromatin (Rakowicz-Szulzynskce et al., 1986). Finally, it is of note that a recent study has demonstrat.ed that intracellular insulin can stimulate RNA and protein synthesis in Xenopus oocytes---results which are again strikingly similar to thosewe have reported in the case of angiotensin II. Indeed, when these studies were extended to the investigation of insulin effects on isolated Xenopus oocyte nuclei, a stimulation of RNA synthesis was observed much as we had observed in the caseof angiotensin II (Miller, 1988). Taken together these observations suggest that intracellular hormonal systemsexist and play an important role in determining the effects of peptide growth factors and possibly other protein hormones as well. Based on the growing number of studies which indicate an intracellular site of action for peptide hormones, I now propose to extend our original definition of intracrine action to include cellular effects mediated by intracellular hor-

Biology

67

mones or hormone fragments, whether or not those hormonal moieties are synthesized b) the target cell itself. This proposed intracrinr mode of peptide action can provide additional information to the cell regarding the growth factor milieu in which it finds itself and. thereby, permit the proper matching of cellular responseto the full panoply of hormones operative in any given circumstance. It is becoming clear that growth factors are multifunctional and possessgrowth-stimulating, growth-inhibiting, vasoactive, or other properties depending on the full complement of factors which are operative on any given cell of any specific genetic composition (Sporn and Roberts, 1988). The internalization and intracrine action of growth factors, therefore, could provide the information transfer which is necessaryif cell responsesare to be tailored to the hormonal environment.

Conclusion

The cellular biology of the cardiovascular systemis complex and involves the interaction of systemic, paracrine, autocrine, and perhaps intracrine factors. This observation has considerable clinical implications in that drugs and interventions aimed at, for example, the systemic level must similarly be analyzed from the point of view of their effects on autocrine. paracrine, and intracrine systemsif they are to be appropriately used. At the same time. multiple new arenas appear to have been opened in medicine’s effort to prevent and control vascular diseasein general and the sequelae of hypertension in particular. Moreover,

the spectrum

of angiotensin

action

involving, as it appears to, systemic, paracrine, autocrine, and intracrine effects, ma) well serve as a paradigm for peptide hormone action in general.

References BARRETT TB, BENDITT EP (1987a) Expression of growth factors and other genes in atherosclerotic plaques and in normal artery. J Mel Cell Cardiol 19 [Suppl IV]: S3. BARRETT TB, BENDITT EP (1987b) 5% (platelet-derived growth factor B chain) gene transcript levels are elrvatrd in human atherosclerotic lesion compared to normal artery. Proc Nat1 Acad Sci USA 841 109%1103. BOUCHE G, Gus N, PRATS H, BALDIN V, TAUBER J-P, TEIWE , AMALRIC F (1987) Basic fibroblast growth factor enters the nucleolus and stimulates the transcription of ribosomal genes in ABAE cells undergoing C,+G, transition. Proc Nat1 Acad Sci USA 81: 677Wi774. BRUNNER HR, LARAOH JH, BAER L, NEWTON MA, GOODWIN FT, KRAKOFF LR, BARD RH, BUHLER FR 11972’ Essential hypertension: renin and aldosterone. heart attack and stroke. N Engl J Med 286: 441449.

68

R. N. Re

BRYAN S, LaGaos L, BROWN J, BYRNE C, RE RN j 1985) Copper-rich nucleoprotrin generated by micrococcal nuclcasc. Biol Trace Element Res 8: 219-229. CELIO MR, iNACAM1 T (1981) Angiotensin II immunoreactivity coexists with rcnin in the juxtaglomerular granulatcells of the kidney. Proc Nat1 Acad Sci USA 78: 389773900. DUNN FG, OIGMAN W, VENTUR HO, MESSERLI FH, KOBRIN I, FROHLICH ED (1984) Enalapril improves systemic, and renal hemodynamics and allows regression ofleft ventricular mass in essential hypertension. Am J Cardio153: 105 --108. DZAU VJ (1988) Vascular renin-antiotensin system in hypertension: new insights into the mechanism of artinns 111 converting enzyme inhibitors. Am J Med 84 [Suppl4A]: 4-8. DZAU VJ, GIBBONS GH (1987) Autocrine-paracrine mechanisms of vascular myocytes in systemic hypertension. Am J Cardiol60: 991-1031. DZAU VJ, RE RN (1987) Evidence for the existence of renin in the heart. Circulation 75 [Suppl I]: 1134-I 136. FOUAD-TARAZI FM, LEIBSON PR (1987) Echocardiographic studies of regression of left ventricular hypertrophy in hypertension. Hypertension 9 [Suppl I]: 1655168. GANTEN D, SCHELLING P, FLUGEL RM, GANTEN C (1975) Effect of angiotensin and an angiotensin antagonist on isorenin and cell growth in 3T3 mouse cells. Int Res Commun Med Sci 3: 327. GEISTERFER A, PEACH MJ, OWENS GK (1988) Angiotensin II induces hypertrophy, not hyperplasice of cultured rat aortic smooth muscle cells. Circ Res 62: 749-756. JIN M, WILHELM MJ, LANG RE, UNGER ‘I‘, LINDPAINTNER K, GANTEN D (1988) Endogenous tissue renin-angiotensin systems Am J Med 84 [Suppl. 3A]: 28~36. KAPLAN NM (1973) Low Renin Hypertension. In: Clinical Hypertension, NM Kaplan (Ed. I_ New York, Mederom, pp 272-287. KAWAHARA Y, SUNAKO M, TSUDO T, FUKUYAKI H, FUKUMOTO Y, TAKAI Y (1988) Angiotensin II induces expression of the c-fos gene through protein kinase C activation and calcium ion mobilization in cultured vascular smooth muscle cells. Biochem Biophys Res Commun 150: 52-59. KHAIRALLAH PA, ROBERTSON AL, DAVILA D ( 1972) Effects of angiotensin II on DNA, RNA and protein synthesis. In: Hypertension (72), Genest J and Koiw E (Eds.). New York, Springer-Verlag, pp 212-220. MAJESKY M, REIDY M, BENDITT E, SCHWARTZ S (1987) Expression ofplatelet-derived growth factor (PDGF) A- and Bchain genes in smooth muscle during repair of arterial injury. J Mol Cell Cardiol 19 [Suppl IV]: S3. MILLER DS (1988) Stimulation of RNA and protein synthesis by intracellular insulin. Science 240: 506511. NAFTILAN AJ, PRATT RE, DZAU VJ (1988) Angiotension II induction of C-&s, c-myc and platelet derived growth factor (PDGF) in vascular smooth muscle cells. (Abstr.) Program of 12th Scientific Meeting gfthe International Sociely qf Hypertension 0592. NICHOLSON AC, MCCAFFREY TA, WEKSLER BB, JAJJAR DP (1987) TGF-B increases c-sis mRNA in endothelial cells and stimulates the production of EC-derived mitogens for smooth muscle cells. J Mol Cell Cardiol 19 [Suppl IV]: S2. NISTER M, HAMMACHER A, MELLSTROM K, SIEGBAHN A, RONNSTRAND L, WESTERMARK B, HELDIN CH (1988) A gliomaderived PDGF A chain homodimer has different functional activities from a PDGF AB heterodimer purified from human platelets. Cell 52: 791-799. OREKHOV (1987) Evidence of antiatherosclerotic action of verapamil from direct effect on arterial cells. Am J Cardiol 59: 495496. OWENS GK (1987) Influence of blood pressure on development of aortic medial smooth muscle hypertrophy in spontaneously hypertensive rats. Hypertension 9: 1788187. OWENS GK, SCHWARTZ SM, MCCANNA M (1988) Evaluation of medial hypertrophy in resistance vessels of spontaneously hypertensive rats. Hypertension 11: 198-207. PENN A, GARTE SJ, WARREN L, NESTA D, MINDACH B (1986) Transforming gem in human atherosclerotic plaque DNA. Proc Nat1 Acad Sci USA 83: 7951-55. PFEFFER JM, PFEFFER MA, MERSKY I, BRAUNWALD E (1982) Regression of left ventricular hypertrophy and prevention of left ventricular dysfunction by captopril in the spontaneously hypertensive rat. Proc Nat1 Acad Sri USA 79: 331&3314. RAKOWICZ-SZULZYNSKCE, RODECK U, HERLYN M, KOPROWSKI H (1986) Chromatin-binding of epidermal growth factor, nerve growth factor and platelet-derived growth factor in cells bearing appropriate surface receptors. Proc Nat1 Acad Sci USA 83: 3728-3732. RE RN (1984) Cellular biology of the renin-angiotensin systems. Arch Intern Med 144: 203772047. RE RN (1987a) Cellular mechanisms of growth in cardiovascular tissue. Am J Cardiol60: 1041-1091. RE RN (1987b) The myocardial intracellular renin-angiotensin system. Am J Cardio159: 56A-58A. RE RN (1987c) The reninangiotensin systems. Med Clin No Amer 71: 877-895. RE RN, BRYAN SE (1984) Functional intracellular renin-angiotensin systems may exist in multiple tissues. Hypertension Clinical and Experimental--Theory and Practice A6 (10 & I 1): 17391742. RE RN, BRYAN SE, LCGROS L., BROWN J, BRYNE C (1985) Copper-rich nucleoprotein generated by micrococcal nuclease. Biol Trace Element Res 8: 219-229. RE RN, FALLON TJ, DZAU VS, QUAY S, HABER E (1982) Renin synthesis by cultured arterial smooth muscle cells. Life Sci 30: 99106. RE RN, MACPHEE AA (1987) Left ventricular cardiac myocytes contain a renin-angiotensin system. (Abstr). Clin Res 35: 7A. RE RN, MACPHEE AA, FALLON JT (1981) Specific nuclear binding of angiotensin II. Clin Sci 61: 245s-247s.

Angiotmsin

Biology

RE RN, PARAB M (1984) Effect of angiotensin II on RNA synthesis by Zola;ed RE RN, VIZARD DL, BROWN J, BRYAN SE (1984a) Angiotensin II receptors

69 nuclei. Life Sci 34: 647-651. in chromatin fragments generated

h> nuclease. Biochem Biophys Res Commun 119: 220. RE RN, VIZARD DL, BROWN J, LEGROS L, BRYAN SE (1984b) Angiotensin II receptors in chromatin. J Hypertension 2 [Suppl3]: 271-273. RICHARDSON WD, I’RINGLE N, MOSLEY MJ, WESTERMARK B, DUBOIS-DALCQ M (1988) A role for platelet-derived growth factor in normal gliogenesis in the central nervous system. Cell 53: 309-319. ROVICATTI U, RE RN (1987) The role of proto-oncogenes in the development of the sequelae of hypertension. Hypertension IO: 358. SCHMIEDER RE, MESSERLI FH, GARAVAGLIA GE, NUNEZ B, MACPHEE AA, RE RN (1988) Does thr renin-angiotensin-aldosterone systems modify cardiac structure and function in essential hypertension? Am J Med 84 [Suppl 3A]: 136-139. SIMONEAN MH, GILL GN (1979) Regulation ofdesoxyribonuclea acid synthesis in bovine adrenocortical cells in culture. Endocrinology 104: 588-595. SPORN MB, ROEERTS AB (1988) Peptide growth factors are multi-functional. Nature 332: 217-219. STARKSEN NF, SIMPSON PC, BISHOPRICK M, COUGHLIN SR, LEE WMF, ESCOBEDO JA, WILLIAMS LT (1986) Cardiac myocyte hypertrophy is associated with c-myc proto-oncogene expression. Proc Nat1 Acad Sci USA 83: 834g-8350. TAUBMAN MB, BERK BC, IZUMO S, ALEXANDER RW, NADAL-GENARD B (1987) Angiotensin II induction oft-fos mRNA in cultured rat aortic smooth muscle cells is independent of stimulation of Na+/H+ exchange. J Mol Cell Cardiol 19 [Suppl IV]: S6. WEISS RJ (1987) Diltiazem-induced left ventricular man regression in hypertensive patients. J Clin Hypertension 3: 135-143. WILLIAMS LT (1988: Stimulation of paracrine and autorrine pathways of cell proliferation by platelet-derived growth factor. Clin Res 36: 5-10.

micrococcal