Participation of angiotensin II and MAP-kinase (Mitogenic-Activated Protein Kinase) in the postnatal renal development of Wistar rats

Author(s)

Ana Paula Coelho Balbi

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2006-08-03

Examining board members

Terezila Machado Coimbra; Emmanuel de Almeida Burdmann; Eduardo Barbosa Coelho; Roberto Silva Costa

• Advisor: Terezila Machado Coimbra

Abstract

Renal development in rats and mice usually begins around the 11st and 12nd day of intrauterine life and continues until postnatal second week. Extracellular matrix (ECM) production has an important role on the glomerular differentiation process. Experimental evidences suggest that angiotensin II (AII) participates on postnatal renal development. Many signals are transmitted from cellular surface to the nucleus through MAPK (Mitogenic-Activated Protein Kinase) cascade. Several effects of AII are related to the activation of these pathways. The aim of this study was evaluate the MAPK expression on the renal cortex during postnatal renal development and the role of AII on the activation of these pathways in rats born from mothers submitted to high salt intake or exposed to losartan during gestation and lactation or during lactation. We also analyzed the effects of those treatments on renal structure and function. Newborn Wistar rats aging 1, 7, 15 and 30 days old were divided into 6 groups for performing of 3 studies: Study 1: Control 1 (C1 ), newborn rats from mothers that received normal salt intake; Experimental 1 (E1), newborn rats from mothers that received increased salt intake; Study 2: Control 2 (C2), newborn rats from mothers exposed to sacarose 2% solution during gestation and lactation; Experimental 2 (E2), newborn rats from mothers exposed to losartan (0,4 g/L) diluted in sacarose 2% solution during gestation and lactation; Study 3: Control 3 (C3), newborn rats from mothers exposed to sacarose 2% solution during lactation; Experimental 3 (E3), newborn rats from mothers exposed to losartan (0,4 g/L) diluted in sacarose 2% solution during lactation. Pups rats were killed and kidneys removed for histological and immunohistochemical studies, evaluation of apoptotic cells by TUNEL and Western blot analysis. The evaluation of α-SMA, fibronectin, p-ERK and p-JNK reactions was performed by scores which reflected mainly the changes in the extent rather than intensity of staining, and number of PCNA, AII and apoptotic positive cells were counted the by glomerulus or grid fields from renal cortex measuring 0.245mm2. Densitometry analysis of bands from Western blot studies for AT 1, AT 2, p-p38 and tubulin was performed using the lmage J computerized program. α-SMA, fibronectin, PCNA, AII and p-ERK expressions in renal cortex were higher on 1 day-old animal and decreased with the renal development. ln study 1, we verified reduced expressions of α-SMA, fibronectin and PCNA on renal cortex of 1 day-old animals from mothers submitted to increased salt intake when compared to the controls of same age. These alterations were associated with the reduction of AII positive cells on renal cortex of these animals. p-ERK expression was lower on renal cortex of 1 day-old animals from E1 group compared to the controls, while p-p38 and p-JNK MAPK expressions were higher on the renal cortex of the 30 day-old animals from E1group when compared to the controls of same age. We also observed higher number of apoptotic cells in renal cortex from these animals. Thirty days-old animals from this group also showed reduction in glomerular filtration rate (GFR) and an increase in blood pressure when compared to the controls of the same age. One and 30 day-old animals from E1 group presented reduction of AT 1 receptor and increase of AT 2 receptor expressions in renal cortex. The treatment with Losartan during gestation and lactation (Study 2) and during lactation (Study 3) provoked increase in fibronectin, PCNA and α-SMA expressions as well in the number of apoptotic cells on renal cortex from 15 and 30 day-old animals compared to the respective contrais. Thirty day-old animals from E2 and E3 groups showed a reduction in AT 1 and an increase in AT 2 expressions, and intense alterations on renal structure characterized by widening of interstitial space of renal cortex, atrophy and tubular lumen dilatation. Moreover, albumin urinary excretion of the 30 days-old animals was noticeably increased. ln conclusion, renal structure and function alterations observed in newborn rats from mothers exposed to treatments that interfere with the activity of RAS was associated with modifications on AT 1 and AT 2 receptors and MAPK expressions during postnatal renal development. (AU)