Heparin inhibits mesenteric vascular hypertrophy in angiotensin II-infusion hypertension in rats.
OBJECTIVE
Chronic infusion with angiotensin II increases blood pressure and activates growth mechanisms to produce hypertrophy of the heart and vessels. In order to better understand mechanisms of angiotensin II induced vascular hypertrophy, this study aimed to determine whether heparin, a potent inhibitor of smooth muscle proliferation mechanisms, was able to inhibit vascular hypertrophy.


METHODS
Angiotensin II (100, 200 or 300 ng/min/kg s.c.) or a saline vehicle control were infused into rats for 14 days. A separate group of animals were co-infused with heparin (0.3 mg/h/kg i.v.) and angiotensin II (200 ng/min/kg s.c.) to test whether hypertension or hypertrophy were antagonized. Blood pressure was measured by tail cuff method and vessel media cross sectional area was measured by morphometry in aorta and mesenteric arteries.


RESULTS
Blood pressure elevation and cardiovascular hypertrophy produced by angiotensin II were strongly dose-dependent. Hypertrophy responses at 14 days of treatment also appeared to be influenced partly by local factors as medial cross sectional area was increased more in mesenteric arteries than in thoracic aorta, and left ventricle weight was least affected. Heparin treatment did not influence the increase of blood pressure in angiotensin II infused animals, but the mesenteric vascular hypertrophy response due to angiotensin II was inhibited by approximately 50%. Inhibition of a modest cardiac hypertrophy and aortic medial hypertrophy did not reach significance.


CONCLUSIONS
Angiotensin II infusion produced vascular medial hypertrophy and increased blood pressure, however the inhibitory effect of heparin on hypertrophy in mesenteric arteries was not mediated through angiotensin II induced vasoconstriction or blood pressure elevation. These data suggest that heparin interferes directly with the hypertrophy mechanism in mesenteric arteries, and that heparin-sensitive growth mechanisms are important in mediating angiotensin induced mesenteric vascular hypertrophy.
Morphology Laboratory, Baker Medical Research Institute, Victoria, Australia. rod.dilley@baker.edu.au
R J
RJ
Dilley
M I
MI
Nataatmadja
D000804:Angiotensin II; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000473:pathology; D001794:Blood Pressure / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005343:Fibrinolytic Agents / Q000627:therapeutic use*; D006493:Heparin / Q000627:therapeutic use*; D006973:Hypertension / Q000139:chemically induced / Q000473:pathology* / Q000517:prevention & control; D006984:Hypertrophy / Q000139:chemically induced / Q000517:prevention & control; D008297:Male; D008642:Mesenteric Veins / Q000187:drug effects / Q000473:pathology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D051381:Rats; D011921:Rats, Inbred WKY; D014662:Vasoconstrictor Agents
D005343:Fibrinolytic Agents; D014662:Vasoconstrictor Agents; D000804:Angiotensin II; D006493:Heparin