cultures incubated for 24 h with 100ZLM phosphoramidon (431 ± 218 PM and 31.1 ± 12.7 fmol mg-'; mean ± s.e.mean, n = 3) or 100 gM pepstatin A (381 ± 169 PM and 19.9 ± 7.8 fmol mg-', n = 3) as compared to controls (355 ± 99 pM and 33.3 ± 9.3 fmol mg-'; n = 3). This observation indicates the absence of an autocrine 'unmasking' effect for ET receptors. 5 HUVSMCs synthesize and secrete immunoreactive ET-1, ET-3 and big ET-1, and possess intracellular levels of immunoreactive mature ET and big ET-1. There is some evidence of common cellular mechanisms between growth factors and vasoconstrictor peptides, suggesting a close relationship between contraction and proliferation. Since the development of various vascular pathologies such as atherosclerosis, hypertension and after vessel injury has been attributed to alterations in the normal growth pattern of VSMCs, the role of ET in these diseases may be of significance.

These organ culture models demonstrate the effects of insulin and PDGF on intimal hyperplasia in IMA and SV representing models for arteriosclerosis and bypass graft stenosis and stressing the role of insulin and growth factors for neointima development.

1 Endothelin (ET) has been implicated in cerebrovasospasm for example, following subarachnoid haemorrhage, and blocking the interaction of ET with its receptors on cerebral vessels, may be of therapeutic benefit. The aim of our study was