ABSTRACT
The aim of the present study was to determine the involvement of atrial natriuretic peptide (ANP) in blood pressure (BP) alterations induced by estradiol treatment. Spontaneously hypertensive rats (SHR) and Wistar rats (WR) were ovariectomized and, after 3 weeks, were injected daily for 4 days with estradiol benzoate (E2; 5 microg/100 g/day) or a vehicle. One day after the last injection, the animals were decapitated, blood was collected, and both right and left atrial appendages were quickly removed for determination of ANP by radioimmunoassay (RIA), or used for ANP mRNA determination. Estradiol treatment induced a significant reduction of blood pressure in SHR, but not in WR. This reduction was correlated with the increase of plasma ANP levels that were significantly increased in E2-treated, compared with vehicle-treated, SHR. E2-treated SHR showed significant increases in ANP concentration in the right and left atria compared to the vehicle-treated animals. These observations were confirmed by ANP mRNA. In summary, the present study shows that short-term estradiol treatment reduces the blood pressure of ovariectomized SHR, but not of WR. This reduction was highly correlated with increased plasma estradiol and ANP levels. These results suggest that ANP is involved in mediating the effect of estradiol on blood pressure reduction.
Subject(s)
Atrial Natriuretic Factor/physiology , Blood Pressure/drug effects , Estradiol/analogs & derivatives , Estradiol/pharmacology , Animals , Antihypertensive Agents/pharmacology , Atrial Natriuretic Factor/genetics , Blood Pressure/physiology , Female , Natriuretic Peptide, Brain/physiology , RNA, Messenger/genetics , RNA, Messenger/metabolism , Radioimmunoassay , Rats , Rats, Inbred SHR , Rats, WistarABSTRACT
The olfactory system plays an important role in the mobilization of animal behaviour, along with the sense of taste. These functions are mediated by a complex olfactory structure composed of peripheral (olfactory epithelium) and central (olfactory bulb) components. Several neuropeptides are synthesized in the olfactory system and are believed to be involved in olfactive processing. Recently, another bioactive substance, atrial natriuretic peptide (ANP), has been demonstrated in the olfactory system. ANP is a potent diuretic, natriuretic and vasorelaxant hormone which, originally, was isolated from mammalian atria, but its gene is expressed in many loci. ANP is only one member of the natriuretic peptide (NP) family, which includes two other peptides, BNP (brain natriuretic peptide) and CNP (C-type natriuretic peptide) derived from different genes. All three peptides show many common features. A high concentration of ANP-immunoreactive varicose fibers has been detected in the rat olfactory nerve layer and glomerular layer of the olfactory bulb (OB). An important group of perykarya and thin varicose fibers has been observed in the olfactory tubercle. We have demonstrated the presence of both ANP precursor and ANP gene transcript in the rat olfactory bulb. In addition to synthesizing ANP, the OB contains ANP transducing receptors coupled to guanylyl-cyclase system. The immunoreactive ANP has also been detected in the rat olfactory mucosa (OM), where ANP has been localized in secretory cells of Bowman's gland and in the cells of the epithelial layer. The relatively low concentration of ANP in OM (2.5 ng/mg protein) suggests a local role for ANP, a hypothesis which is strengthened by the presence of ANP high affinity receptors in this tissue. Although the role of ANP in the olfactory system is not yet clear, ANP has been shown to modulate olfactory bulb mitochondrial membrane activity and to be involved in the olfactive function.