Impaired paracrine effect of endothelin-1 on vascular smooth muscle in streptozotocin-diabetic rats.
OBJECTIVE
This study was to examine the effect of streptozotocin-induced diabetes on endothelin-1 and its receptors in the mesenteric artery and in the thoracic aorta.


METHODS
Diabetes was induced in SD rats by streptozotocin. Insulin was given subcutaneously. Endothelin-1 levels in the plasma, thoracic aorta and mesenteric artery were measured using radioimmunoassay. The Bmax and Kd values of endothelin-1 receptors in the mesenteric artery and in the thoracic aorta were analyzed using Scatchard plot analysis. Preproendothelin mRNA levels were examined using RT-PCR.


RESULTS
Endothelin-1 levels in the mesenteric artery (83.6 +/- 6.9 pg/mg protein) and in the thoracic aorta (73.9 +/- 8.2 pg/mg protein) increased in 2 week diabetic rats compared with both control (51.8 +/- 5.3, 46.3 +/- 5.9 pg/mg protein) and insulin treated rats (65.6 +/- 8.1, 48.1 +/- 4.2 pg/mg protein) but not in 4 week diabetic rats. There was no change in plasma endothelin-1 levels in these diabetic rats. The RT-PCR results indicated that preproendothelin mRNA levels in the mesenteric artery (0.38 +/- 0.02 vs 0.52 +/- 0.05 units) and in the thoracic aorta (0.45 +/- 0.06 vs 0.62 +/- 0.03 units) decreased in 4 week diabetic rats but not in 2 week diabetic rats. A significant increase in Kd and Bmax of endothelin receptors in the mesenteric artery and in the thoracic aorta was observed in both 2 week (about 70%) and 4 week (80-85%) diabetic rats. Insulin replacement reversed the effects of diabetes on endothelin-1 peptide contents, preproendothelin mRNA levels and the binding activity in the blood vessels.


CONCLUSIONS
Increased endothelin peptide content with no change in mRNA or decreased mRNA levels with no change in peptide content together with increased receptor binding sites and affinities might imply a decrease in endothelin release and therefore an impaired paracrine effect of endothelin on vascular smooth muscles in these STZ-diabetic rats.
Wu
S Q
SQ
Department of Physiology, Faculty of Medicine, University of Hong Kong, China.
Tang
F
F
D000704:Analysis of Variance; D000818:Animals; D001013:Aorta, Thoracic / Q000737:chemistry / Q000378:metabolism; D015139:Blotting, Southern; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D019332:Endothelin-1 / Q000097:blood / Q000378:metabolism*; D016232:Endothelins / Q000235:genetics; D008297:Male; D008638:Mesenteric Arteries / Q000737:chemistry / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000737:chemistry / Q000378:metabolism*; D019899:Paracrine Communication; D011485:Protein Binding; D011498:Protein Precursors / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D017466:Receptors, Endothelin / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D019332:Endothelin-1; D016232:Endothelins; D011498:Protein Precursors; D012333:RNA, Messenger; D017466:Receptors, Endothelin