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(Hypertension. 2001;37:692.)
© 2001 American Heart Association, Inc.

Scientific Contributions

Differentiation of Brain Angiotensin Type 1a and 1b Receptor mRNAs

A Specific Effect of Dehydration

Yanfang Chen; Mariana Morris

From the Department of Pharmacology and Toxicology, Wright State University School of Medicine, Dayton, Ohio.

Correspondence to Mariana Morris, PhD, Wright State University, School of Medicine, Pharmacology/Toxicology, PO Box 927, Dayton, OH 45401-0927. E-mail mariana.morris{at}wright.edu

The objective was to examine the effect of dehydration on the expression of the angiotensin type 1 (AT₁) receptor subtype mRNAs in mice by using an in situ hybridization method. The method used free-floating brain sections with ³⁵S-labeled probes specific for the untranslated 5' (AT_1a) and 3' (AT_1b) regions. AT_1a and AT_1b mRNA levels in the subfornical organ (SFO) and anterior third ventricle (AV3V) were quantified by using a phosphor-imaging system. Emulsion autoradiography with cresyl violet counterstaining was used to show cellular expression. Adult male C57BL mice (25 to 30 g) were given water ad libitum or were deprived of water for 48 hours. Dehydration produced increases in plasma osmolality (349±6 versus 314±4 mOsm/kg) and hematocrit (58±2% versus 47±1%). In situ hybridization showed that there was expression of AT_1a and of AT_1b mRNA in SFO and AV3V. Dehydration produced an increase in AT_1a mRNA in both regions, with no changes noted for AT_1b. AT_1a mRNA was increased in the AV3V region from 0.3±0.2 to 0.7±0.2 µCi/g and in the SFO from 0.6±0.3 to 1.0±0.2 µCi/g. These results provide information regarding the localization and physiological importance of a subset of angiotensin receptors that are important in volume and blood pressure regulation. AT_1a and AT_1b mRNAs showed a similar pattern of expression in rostral forebrain osmosensitive regions. However, osmotic/volume stimulation with dehydration produced specific activation of AT_1a receptors. This verifies the role of AT_1a receptors in volume regulation but raises a question concerning the physiological role of the AT_1b subtype.

Key Words: angiotensin II • brain • hybridization • receptors, angiotensin • renin-angiotensin system

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