Tissue-specific changes in angiotensin II receptors in streptozotocin-diabetic rats

While there have been reports on changes in the renin-angiotensin system and angiotensin II (AT) receptors in diabetes, there is no agreement on the nature of these changes. This study has characterised specific AT receptors in the heart, kidney, liver and adrenal glands of the streptozotocin (STZ)-diabetic rat using radioligand binding studies with the radioligand I-125-[Sar(1),Ile(8)]-angitoensin II. Left Ventricular AT receptor density increased by 135% 4 weeks after treatment and by 206% 12 weeks after treatment; in the liver, AT receptor density increased by 476% (4 weeks) and 263% (12 weeks) and in the adrenal gland by 236% (4 weeks) and 109% (12 weeks). In contrast, renal AT receptor density decreased by 49% (4 weeks) and 36% (12 weeks). Competition-displacement assays with losartan, an AT1-selective ligand, showed that the proportion of AT receptor subtypes remained unchanged. STZ treatment decreased plasma angiotensinogen by 72% (4 weeks) and 67% (12 weeks) and increased plasma renin concentration after 12 weeks; plasma renin activity and aldosterone concentrations remained unchanged. Treatment with human insulin (5 U/day) attenuated changes in plasma angiotensinogen and AT receptor density except in the left Ventricle. We conclude that there are major changes in AT receptors in the STZ-diabetic rat that are tissue-specific and time-dependent. Plasma angiotensinogen and renin secretion change in directions that result in the maintenance of plasma renin activity and aldosterone concentration.