Expression of Angiotensin II Receptor Subtypes AT1A and AT1B in Enriched Fractions of Dispersed Rat Pituitary Cells

Differential evaluation of angiotensin II (Ang II) receptors (AT 1A, AT 1B and AT2) expression was performed in dispersed adenohypophyseal cells fractionated by unit gravity sedimentation. Binding of [125I-Sar1-Ile8]-Ang II and its displacement by specific nonpeptidic AT1 (DUP753) and AT2 (PD123319) antagonists was monitored throughout the gradient. Quantification of mRNA levels corresponding to both ATi receptor subtypes (AT 1A and AT1B) was achieved by reverse transcriptase polymerase chain reaction (RT-PCR) amplification in the presence of an AT1 receptor mutant cRNA as internal standard. Fractions were characterised by radioimmunoassay for the five major anterior pituitary hormones and by counting immunocytochemically labelled cells. Quantification of AT1 receptor subtype mRNA levels was also performed in four hypophyseal cell lines secreting prolactin, growth hormone, corticotropin and a gonadotropin subunit. As already described for the whole pituitary, AT1B receptor mRNA is predominantly expressed (80% of total ,AT 1A + ,AT 1B receptor mRNA content), whereas ,AT 1A is expressed at lower level (20%) in dispersed pituitary cells. Most AT1 receptor mRNA and binding co-elute with fractions enriched in lactotropes and corticotropes. In contrast to ,AT 1B, ATtA receptor mRNA is not present in heavier populations of lactotropes or in somatomammotropes. Low ,AT 1B mRNA levels are detected in GH4C1 and in GC cells, two clones which secrete respectively prolactin and growth hormone. In contrast, no AT1 receptor mRNA expression was found in two other cell lines, AtT20 and (XT3.1, which produce pro-opiomelanocortin and gonadotropin. It is concluded that expression of AT1 receptor subtypes is heterogeneous in different populations of lactotropes and corticotropes.