DIFFERENTIAL-EFFECTS OF RAT PREGNANCY ON UTERINE AND LUNG ATRIAL-NATRIURETIC-FACTOR RECEPTORS

We investigated if the refractoriness to the tocolytic effects of atri al natriuretic factor (ANF) during rat pregnancy is due to a downregul ation of one or both guanylyl cyclase (GC)-coupled GC-A and GC-B ANF r eceptors; lungs were used as controls. Uteri and lungs of virgin, preg nant (days 7, 16, and 21), and day 2 postpartum rats expressed mRNAs f or GC-A and GC-B as well as GC-uncoupled ANF-C receptors. GC-B recepto r protein was more abundant than GC-A in uteri; the reverse was the ca se in lungs. Pregnancy decreased uterine mRNAs and proteins for GC-A a nd GC-B receptors as well as the effects of ANF and C-type natriuretic peptide (CNP) on uterine GC activity; lung ANF receptors and effects of ANF and CNP on lung GC activity were not modulated by pregnancy. It is concluded that pregnancy induces organ-specific modulation of ANF receptors and a downregulation of ANF-GC receptors would minimize inte rference with uterine motility during pregnancy.