Dissociation of the contractile and hypertrophic effects of vasoconstrictor prostanoids in vascular smooth muscle.

G.W Dorn,M.W Becker,M.G Davis

doi:10.1016/s0021-9258(18)35848-4

G.W Dorn, M.W Becker + Show 1 more

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https://doi.org/10.1016/s0021-9258(18)35848-4

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Abstract

To more clearly define the physiologic roles of thromboxane (TX)A2 and primary prostaglandins (PG) in vascular tissue we examined vascular contractility, cell signaling, and growth responses. The growth-promoting effects of (15S)-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid (U46619; TXA2 agonist), PGF2 alpha, and PGE2 consisted of protein synthesis and proto-oncogene expression, but not DNA synthesis or cell proliferation. U46619 contracted rat aortas and increased cultured rat aortic vascular smooth muscle cell intracellular free calcium concentration [Ca2+]i, [3H]inositol monophosphate (IP) accumulation, myosin light chain phosphorylation, and protein synthesis ([3H]leucine incorporation) with EC50 values ranging from 10 to 50 nM. Each of these responses was inhibitable with the TXA2 receptor antagonist [1S]1 alpha,2 beta(5Z),3 beta,4 alpha-7-(3-[2- [(phenylamino)carbonyl]hydrazino]methyl)-7-oxabicyclo[2.2.1]hept-2- yl-5-heptenoic acid (SQ29548). In contrast, PGF2 alpha increased [Ca2+]i, [3H]IP, and protein synthesis with EC50 values of 30-230 nM but contracted rat aortas with an EC50 of 4800 nM. PGE2 increased [Ca2+]i, [3H]IP accumulation, protein synthesis, and contracted rat aortas with EC50 values of 2.5-3.5 microM. TXA2 receptor blockade prevented PGF2 alpha- and PGE2-induced aortic contraction and cell myosin light chain phosphorylation, but not cell signaling or protein synthesis. Binding studies to vascular smooth muscle TXA2 receptors using 1S-[1 alpha,2 beta(5Z),3 alpha(1E,3S),4 alpha]-7-(3-[3-hydroxy-4-(p- [125I]iodophenoxy)-1-butenyl]7-oxabicyclo[2.2.1]hept-2-yl)-5-hepte noic acid ([125I]BOP) showed U46619, SQ29548, PGF2 alpha, and PGE2 competition for TXA2 receptor binding at concentrations similar to their EC50 values for aortic contraction, while binding competition with [3H]PGF2 alpha and [3H]PGE2 demonstrated the specificity of [125I]BOP and SQ29548 for TXA2 receptors. The results suggest that 1) PGF2 alpha- and E2-stimulated vessel contraction is due to cross-agonism at vascular TXA2 receptors; 2) PGF2 alpha stimulates TXA2 receptor-independent vascular smooth muscle protein synthesis at nanomolar concentrations, consistent with an interaction at its primary receptor; and 3) TXA2 is a potent stimulus for vascular smooth muscle contraction and protein synthesis. We suggest that the main physiologic effect of PGF2 alpha may be as a stimulus for vascular smooth muscle cell hypertrophy, not as a contractile agonist.

Highlights

Tomoreclearlydefinethe physiologic roles of Thromboxane A, (TXA,),’ prostaglandin Fz, (PGF,), and thromboxane (TX)A2and primary prostaglandins (PG)prostaglandin E, (PGE,) are powerful vasoconstricting agents in vascular tissue we examined vascular contractility, in a variety of species and vascular bedsand havebeen cell signaling, and growtrhesponses
Thano)prosta-52,13E-dienoicacid (U46619; TXA, ag- through the use of radioligand binding to cultured vascular onist), PGF, and PGE, consisted of protein synthesis and proto-oncogene expression,but not DNA synthesis or cell proliferation
We show that pharmacologic blockade of vascular receptor bindingat concentrations similar to thEeCi6r0 smooth muscle TXA, receptors prevents contraction andmyvalues for aortic contraction, while binding competi- osin light chain phosphorylation induced by prostaglandins tion with [‘HIPGF, and [3H]PGE2demonstrated the FPaand E, without inhibiting increases in intracellular free specificity of [‘261]BOPand SQ29548 forTXA, recep- calcium ([Ca”]i) or hydrolysis of phosphatidylinositol stimtors

Summary

RESULTS

Phorylated and nonphosphorylated myosin light chains were resolved Prostanoid-stimulated Rat Aortic Contraction and Myosin by glycerol-ureaelectrophoresis as described by Persechini et al [16]. We examined the effects of thromboxane AP receptor blockade on prostanoid-stimulated myosin light chain phosphorylation in vascular smooth muscle cells cultured from rat aorta. Binding of Vasoconstrictor Prostanoids to Rat Aortic VascularSmooth MuscleThromboxane A2 andProstaglandin Receptors-Two explanations for prostaglandin-induced, thromboxane Az receptor-mediated vasoconstriction at high concentrations could be: 1) PGF,, and PGEz interact with high affinity at TXA, receptors but act as partialagonists or 2) PGF,, and PGE, are full agonists with very low affinity for TXAz receptors To differentiate between these two possible mechanisms we examined the interactions of primary prostaglandins and thromboxane analogues at rat vascular smooth muscle TXA, receptors in competition binding studies using ['2sI]BOP, [3H]PGF2,,and [3H]PGEP.We have previously demonstrated that the TXA2 mimetic [12sI]BOPbinds to a single site on cultured vascular smooth muscle cells with a Kd of approximately 260 PM and a binding capacity of over 7000 sites/cell [15].

Effects of Vasoconstrictor Prostanoids on Vascular Smooth

Findings

DISCUSSION