The concept that the gastrointestinal system plays an important role in the regulation of renal Na excretion has been hypothesized for over 30 years. While there is evidence for both neural and endocrine mechanisms participating in this signaling pathway, the nature of this critical gastrointestinal-renal communication axis for regulating Na+ balance is not well understood. Recently, the GI peptide uroguanylin has received attention as a putative """"""""intestinal natriuretic hormone"""""""", that serves to match salt excretion to salt intake. In support of an important role for uroguanylin, data from our lab using knockout mice have demonstrated that uroguanylin-deficiency results in a blunted natriuretic response to enteral NaCl load and a modest degree of hypertension. Studies have also shown that uroguanylin-deficiency dramatically exacerbates the hypertension induced by chronic angiotensin II infusion, suggesting that derangements in uroguanylin-dependent signaling mechanisms may result in a predisposition for the development of hypertension. Although a role for uroguanylin as a circulating humoral factor has been postulated, available evidence indicates that this may not be the case. Indeed, our preliminary experiments provide compelling evidence that uroguanylin interacts with renal nerve activity to regulate renal Na+ excretion in response to alterations in salt intake. In addition, our data clearly demonstrate that at least one major target of uroguanylin-dependent signaling is the proximal tubule. Our guiding hypothesis for this proposal is that the natriuretic response to increased NaCl intake involves the paracrine or autocrine action of uroguanylin, interacting with a hepatorenal neural reflex. Specifically, we postulate two possible roles for uroguanylin: 1) that it participates in the effector limb of a neural signal to the kidney and such changes in efferent renal sympathetic nerve activity result in changes in the local renal production of uroguanylin; a likely target for this effect is the proximal tubule Na/H exchanger; and/or 2) that uroguanylin produced in the Gl-tract participates in the initiation of the afferent component of the hepatorenal reflex; a likely target for this effect is the Na-K-2Cl cotransporter. The studies described herein will take advantage of several different gene knockout mice to address our specific aims: 1) to determine to what extent a natriuretic signal originating in the GI tract is transmitted to the kidney through a neural reflex, and whether uroguanylin is a necessary effector component in the kidney; 2) to determine to what extent proximal tubule Na/H exchange is involved as a target of uroguanylin-mediated inhibition of sodium transport; 3) to determine to what extent the Na-K-2Cl cotransporter is required for initiation of a hepatorenal neural reflex mediating renal Na+ excretion; and 4) to determine to what extent uroguanylin-deficiency exacerbates experimentally induced hypertension. These studies, which combine unique animal models with state-of-the-art techniques, will provide important insights regarding Gl-renal signaling mechanisms that help to maintain Na+ balance, and will help to elucidate the relative importance of uroguanylin in regulating normal Na+ balance and blood pressure, as well as in the pathogenesis of hypertension.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK057552-08
Application #
7455171
Study Section
Hypertension and Microcirculation Study Section (HM)
Program Officer
Ketchum, Christian J
Project Start
2000-04-01
Project End
2010-06-30
Budget Start
2008-07-01
Budget End
2010-06-30
Support Year
8
Fiscal Year
2008
Total Cost
$213,951
Indirect Cost
Name
University of Cincinnati
Department
Physiology
Type
Schools of Medicine
DUNS #
041064767
City
Cincinnati
State
OH
Country
United States
Zip Code
45221
Lorenz, John N; Oshiro, Naomi; Loreaux, Elizabeth L et al. (2012) DOCA-salt hypertension does not require the ouabain-sensitive binding site of the ?2 Na,K-ATPase. Am J Hypertens 25:421-9
Lorenz, John N; Lasko, Valerie M; Nieman, Michelle L et al. (2011) Renovascular hypertension using a modified two-kidney, one-clip approach in mice is not dependent on the *1 or *2 Na-K-ATPase ouabain-binding site. Am J Physiol Renal Physiol 301:F615-21
Wansapura, Arshani N; Lasko, Valerie M; Lingrel, Jerry B et al. (2011) Mice expressing ouabain-sensitive ?1-Na,K-ATPase have increased susceptibility to pressure overload-induced cardiac hypertrophy. Am J Physiol Heart Circ Physiol 300:H347-55
Lorenz, John N (2010) Chymase: the other ACE? Am J Physiol Renal Physiol 298:F35-6
Jagatheesan, Ganapathy; Rajan, Sudarsan; Schulz, Emily M et al. (2009) An internal domain of beta-tropomyosin increases myofilament Ca(2+) sensitivity. Am J Physiol Heart Circ Physiol 297:H181-90
Wansapura, Arshani N; Lasko, Valerie; Xie, Zijian et al. (2009) Marinobufagenin enhances cardiac contractility in mice with ouabain-sensitive alpha1 Na+-K+-ATPase. Am J Physiol Heart Circ Physiol 296:H1833-9
Prasad, Vikram; Bodi, Ilona; Meyer, Jamie W et al. (2008) Impaired cardiac contractility in mice lacking both the AE3 Cl-/HCO3- exchanger and the NKCC1 Na+-K+-2Cl- cotransporter: effects on Ca2+ handling and protein phosphatases. J Biol Chem 283:31303-14
Lorenz, John N; Loreaux, Elizabeth L; Dostanic-Larson, Iva et al. (2008) ACTH-induced hypertension is dependent on the ouabain-binding site of the alpha2-Na+-K+-ATPase subunit. Am J Physiol Heart Circ Physiol 295:H273-80
Loreaux, Elizabeth L; Kaul, Baksho; Lorenz, John N et al. (2008) Ouabain-Sensitive alpha1 Na,K-ATPase enhances natriuretic response to saline load. J Am Soc Nephrol 19:1947-54
Gawenis, Lara R; Bradford, Emily M; Prasad, Vikram et al. (2007) Colonic anion secretory defects and metabolic acidosis in mice lacking the NBC1 Na+/HCO3- cotransporter. J Biol Chem 282:9042-52

Showing the most recent 10 out of 32 publications