1. Metabolic Consequences of Deoxycorticosterone Acetate (DOCA)-Salt in Mice Beth A. Buehrer, Justin L. Grobe, Aline M. Hilzendeger, and Curt D. Sigmund Department of Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, IA FIGURE 1: The Renin-Angiotensin System (RAS) The RAS is most recognized for its role in regulating blood pressure and fluid balance. The system is present in blood circulation as well as in the brain. FIGURE 2: The DOCA-salt model of Low-Renin Hypertension (A) Despite a large contribution of low-renin hypertension to the human primary hypertensive population, few animal models of this state exist. One of the few models of low-renin hypertension is the DOCA-salt model, where excess DOCA (a steroid precursor of aldosterone-B) is delivered to an animal, and the animal is supplied with a high sodium diet. This treatment results in hypertension that is mediated through the brain RAS (C), vasopressin, and the sympathetic nervous system, and correlates with a decrease of renal renin production. From Laragh, Circulation, 1971 From Itaya et al., Am, J. Physiol. 1986; 251: H261-H268. DOCA Corticosterone 18-OH Corticosterone Aldosterone 11β-hydroxylase 18-hydroxylase 18-Oxidase A BC FIGURE 3: DOCA-salt causes elevated metabolic rate DOCA-salt treatment in male C57BL/6J mice results in an elevation in metabolic rate when compared to baselines of the mice or sham-treated control mice. This effect holds true whether data are expressed as raw oxygen consumed (A), oxygen consumption normalized to body mass (B), or as heat produced, which takes into consideration the source of calories burned, as determined by simultaneous carbon dioxide production (C). * P<0.05 vs. sham. † P<0.05 vs. baseline. FIGURE 4: Food intake is unchanged, but fluid balance is greatly altered by DOCA-salt treatment Over three weeks of treatment, sham animals gain weight, but DOCA-treated animals fail to gain weight (A). Food, and thereby energy intake, is unchanged by DOCA treatment (B-D). Fluid intake is greatly elevated by DOCA treatment (E), as is sodium intake (F) when 0.15 M NaCl is offered as a drink choice. Large volumes (G) of dilute urine (H) are produced in response to DOCA. Urinary sodium concentration is depressed by DOCA (I), but because of the large urine volume, total daily urinary sodium loss is elevated (J). Urinary potassium concentration is greatly depressed with DOCA (K), but total daily potassium loss is normal (L). Serum sodium concentrations are elevated (M) and serum potassium concentrations are depressed (N), as is expected with stimulation of renal mineralocorticoid receptors. * P<0.05 vs. sham. † P<0.05 vs. baseline. FIGURE 5: Hypertension contributes to hydromineral, but not metabolic, consequences of DOCA-salt treatment Chronic treatment with hydralazine (500 mg/L in drink solutions), a direct vasodilator, normalized the mild hypertension (A; 2-way RM ANOVA, Group P=0.284, Time P<0.001, Interaction P=0.022) and bradycardia (B; 2-way RM ANOVA, Group P<0.001, Time P<0.001, Interaction P<0.001) caused by DOCA-salt treatment, but had no effect on the elevated metabolic rate (C), nor the body mass or food intake behavior (D) in these mice. In contrast, hydralazine attenuated the fluid turnover consequences of DOCA treatment (E). * P<0.05 vs. sham, † P<0.05 vs. baseline. ABC ED FIGURE 6: Metabolic consequences of DOCA-salt treatment are dependent upon RAS signaling within the brain Compared to chronic intracerebroventricular (i.c.v.) infusion of artificial cerebrospinal fluid (aCSF), chronic i.c.v. delivery of Losartan (5 ug/hr), an AT1 receptor antagonist, attenuated metabolic rate during DOCA-salt treatment regardless of normalization method (A-B, D-E), but had no effect on respiratory quotient, and thus energy source (C). * P<0.05 vs. Sham+aCSF. † P<0.05 vs. DOCA+aCSF Chronic i.c.v. drug FIGURE 7: Proposed model DOCA-salt treatment results in elevations in metabolic rate and hypertension. Inhibition of RAS activity within the brain through central delivery of the AT1 receptor antagonist, Losartan, is known to block DOCA-salt increases in blood pressure (Kubo 2000, Park 2001), and here we show that it also blocks the metabolic effects of DOCA-salt treatment. In contrast, treatment with a direct vasodilator, hydralazine, attenuates the blood pressure but not the metabolic effects of DOCA treatment. Losartan Funding: BAB was supported through a fellowship from the University of Iowa Research Center for Undergraduates. JLG was supported through an Institutional Training Grant to the Iowa Cardiovascular Center (DK007690, PI: John B. Stokes), and through a K99/R00 Pathway to Independence Award from the NIH (HL098276). DX was supported through a Predoctoral Fellowship from the American Heart Association. This work was supported through research grants from the NIH: HL084207, NS24621, HL048058, and HL076421 to CDS.