Renin knockout rat: control of adrenal aldosterone and corticosterone synthesis in vitro and adrenal gene expression

Abstract

The classic renin-angiotensin system is partly responsible for controlling aldosterone secretion from the adrenal cortex via the peptide angiotensin II (ANG II). In addition, there is a local adrenocortical reninangiotensin system that may be involved in the control of aldosterone synthesis in the zona glomerulosa (ZG). To characterize the long-term control of adrenal steroidogenesis, we utilized adrenal glands from renin knockout (KO) rats and compared steroidogenesis in vitro and steroidogenic enzyme expression to wild-type (WT) controls (Dahl S rat). Adrenal capsules (ZG; aldosterone production) and subcapsules [zona reticularis/fasciculata (ZFR); corticosterone production] were separately dispersed and studied in vitro. Plasma renin activity and ANG II concentrations were extremely low in the KO rats. Basal and cAMP-stimulated aldosterone production was significantly reduced in renin KO ZG cells, whereas corticosterone production was not different between WT and KO ZFR cells. As expected, adrenal renin mRNA expression was lower in the renin KO compared with the WT rat. Real-time PCR and immunohistochemical analysis showed a significant decrease in P450aldo (Cyp11b2) mRNA and protein expression in the ZG from the renin KO rat. The reduction in aldosterone synthesis in the ZG of the renin KO adrenal seems to be accounted for by a specific decrease in P450aldo and may be due to the absence of chronic stimulation of the ZG by circulating ANG II or to a reduction in locally released ANG II within the adrenal gland. aldosterone; corticosterone; adrenal cortex; renin; knockout rat ALDOSTERONE IS SYNTHESIZED in the zona glomerulosa (ZG) of the adrenal gland and is stimulated by angiotensin II (ANG II), ACTH, and potassium (5,8,25). Aldosterone is critical in the control of renal sodium and potassium excretion. The classic renal renin-angiotensin-aldosterone system (RAAS) is well known as a major regulator of sodium and potassium balance. However, it has been known for decades that the adrenal cortex also expresses a local RAAS that operates independently of the renal RAAS (2,7,9,14,16,26,28). One theory is that adrenal renin-generated ANG II mediates the ZG response to increases in plasma potassium, and this is mediated by expression of the angiotensin AT 1 receptor (5,9,14,26,29).The development of the renin knockout (KO) rat provides a unique opportunity to begin to evaluate these phenomena (13).In the current study, we have begun this process by evaluating the aldosterone and corticosterone response to cAMP in vitro by the measurement of adrenal steroidogenic gene expression and by morphological examination of adrenal zonation by immunohistochemical analysis of the two major late-pathway steroidogenic enzymes: P450aldo (CYP11B2) that mediates the conversion of corticosterone to aldosterone in the ZG and P45011␤ (CYP11B1) that mediates corticosterone production in the zona fasciculata/reticularis (ZFR) (8). MATERIALS AND METHODS Generation of the renin KO rat. All experiments were approved by the Medical College o...

Renal sodium transport in renin-deficient Dahl salt-sensitive rats

“…18 This mechanism may be important in the Ren −/− rats since it was previously shown that serum potassium was significantly increased in Ren −/− rats. 41 The authors also demonstrated in vitro that the corticosterone basal levels and production by zona reticularis/fasciculata cells in response to cyclic adenosine monophosphate (cAMP) was unaffected in the Ren −/− rat compared with the Ren +/+ controls. Our in vivo experiments accordingly revealed equal plasma levels of corticosterone in Ren −/− and Ren +/+ littermates.…”

“…For instance, recent studies using this model defined basal and cAMP-stimulated aldosterone production in the zona glomerulosa cells. 41 Further characterization of sodium balance in these animals is required as we hypothesize that low systemic RAAS activity is the cause of very low blood pressure (~60 mmHg) in these animals. 11 …”

Pathophysiology and genetics of salt-sensitive hypertension

“…It was observed that Ren −/− rats experienced a reduction of about 50 mmHg in their blood pressure in comparison to Ren +/- littermates, when on low-salt diet (0.4% NaCl) ( Moreno et al, 2011b ). In their pivotal work, Moreno and colleges suggested that the decrease in basal blood pressure of renin knockout rats was due to an attenuation in the steroidogenesis process occurring in the zona glomerulosa of the adrenal cortex ( Raff et al, 2015 ). Furthermore, the expression and activity of renal sodium channels and transporters were significantly dysregulated in renin-deficient salt-sensitive rats ( Pavlov et al, 2016 ).…”