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renergic receptors and f a t cells: differential recruitment by physiological amines and homologous regulations. Obes Res. 1995;3(Suppl4):507S-514S. The control of fat cell lipolysis by the catecholamines involves at least four different adrenoceptor subtypes; three p (p 1-, p2-, and P3-ARs) and one a2-adrenoceptor(aZ-AR). The physiologicalimportanceof the p-and a2A-ARs varies according to the species, the sex, the age, the anatomical locationof fat deposits and the degree of obesity in humans and animals. The physiological amines operate through differential recruitment of these sites on the basis of their relative affinities. This point has been assessed by in vitro studies andhas partly beenconfimedininvivoexperiments using selecteddp-AR antagonists and in situ microdialysis.The affinity of the P3-ARfor catecholamines is less than that of the classical pl-and (32-ARs in the various species investigated. Conversely,it is the a2-AR which exhibit the highest affinity for thephysiologicalamines in all fat cells. The relative order of affinity of the various fat cell ARs for the physiologicalamines defined in binding studies and in vitro assaysisa2>pll j32>j33fornorepinephrineanda2 > fl2 > p l > p3 for epinephrine. When considering differential p-AR recruitment by catecholamines, it is the p1-AR which is always activated at the lowest norepinephrine levels,whateverthe species,while the activationof the p3-AR requires higher norepinephrinelevels. In additionto the differential recruitment, differential regulation by hormones could also occur for eachfat cell AR subtype. The a2-and P3-ARs are less prone to desensitization and down-

Aggregating human platelets induce VEGF mRNA expression in cultured SMC and the subsequent release of VEGF protein. This effect can be attributed to a supra-additive action of PDGF(AB) and TGF-beta(1) and may represent a novel mechanism by which platelets contribute to the recovery of the endothelial lining at sites of balloon-injured arteries.

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