Effects of Tomatine on Aldosterone Release from Zona Glomerulosa Cells in 5/6 Nephrectomized Male Rats

Abstract

Chronic kidney disease (CKD) is a common risk. Tomatine (Tt) is a glycoalkaloid extracted from tomato plants. To study the CKD, the 5/6 nephrectomy (5/6 NX) in rats was performed. The purpose of this study was to clarify the actions of Tt on the function of zona glomerulosa (ZG) cells. Rat ZG cells were prepared and treated with Tt in the presence or absence of angiotensin II (Ang II). The release of aldosterone was dose-dependently decreased by the administration of Tt. Then, male rats were divided into six groups including [1] sham+ oil, [2] sham+Tt (0.4 mg/kg), [3] sham+Tt (2 mg/kg), [4] 5/6 NX+oil, [5] 5/6 NX +Tt (0.4 mg/kg), and [6] 5/6 NX +Tt (2 mg/kg). Six weeks after 5/6 NX and sham-operation, Tt and oil were injected subcutaneously once per day for 7 days. In nephropathy rats, both blood creatinine and urine nitrogen increased as the markers of renal dysfunction. With metabolic cage housing, the water consumption and urine output declined after treatment of Tt in rats. After injection of Tt, the mean arterial pressure was slightly declined. The circulating levels of Na^+, K^+, and Cl^- were not altered but the osmolality was significantly raised in 5/6 NX rats. The plasma and medium levels of aldosterone were measured by radioimmunoassay. The levels of plasma aldosterone in intact groups were not altered, but markedly raised in 5/6 NX groups after Tt treatment. Immunoblotting was performed to analyze the protein expressions of angiotensin II Type 1 receptor (AT1R), steroidogenic acute regulatory protein (StAR), and cholesterol side-chain cleavage (P450scc) enzyme in rat adrenocortex tissue. These results indicated that the expression of AT1R was up-regulated in 5/6 NX rats but decreased by the administration of Tt. These results suggested that Tt may act directly on ZG cells to reduce the release of aldosterone in response to angiotensin II via attenuating the cyclic adenosine monophosphate (cAMP) pathway. The reduction of Tt on aldosterone release in CKD rats induced by 5/6 NX were at least in part due to the inhibition of Tt on the elevated protein expression of AT1R in CKD rats.