Effect of pregnancy on activation of central pathways following atrial distension

Abstract

Stimulation of the atrial volume receptors increases neural traffic to the ventrolateral medulla, which in turn sends output to, and receives input from, the lateral hypothalamic area. An integrated reflex and hormonal response is thus initiated. We wished to investigate first whether atrial distension results in activation of selected nuclei in the forebrain and, second, whether pregnancy modifies this response. Rats were implanted with indwelling intracardiac balloons positioned at the superior vena caval/right atrial junction. One week later, the balloons were inflated. The animals were then anesthetized, their brains fixed by perfusion, and the tissue prepared for visualization of c-fos activity. Atrial distension caused a significant increase in c-fos expression in the paraventricular nucleus, the medial preoptic area, and the lateral septum. This response was markedly attenuated in the pregnant animals. In conclusion, during pregnancy central pathways that are normally activated in responses to volume expansion, fail to respond to atrial distension. We propose that this allows blood volume to increase in the pregnant animal, without triggering homeostatic mechanisms.

Effect of pregnancy and 5α-pregnan-3α-ol-20-one on atrial receptor afferent discharge in rats

“…Previous work has shown that activation of neurons in the hypothalamus in response to atrial receptor activation is reduced in pregnant rats compared with virgin rats (2). Thus the homeostatic mechanism that keeps fluid volume in check is suppressed during pregnancy.…”

“…We have shown that reflex control of renal function by the atrial volume receptors is attenuated during pregnancy such that the increase in sodium excretion and urine volume normally seen in response to atrial distension does not occur (8). In addition, there is a loss of activation of central components of the reflex pathway in response to atrial receptor stimulation in pregnant animals (2). These observations have led us to suggest that the homeostatic mechanisms that operate to maintain fluid balance are attenuated in the pregnant animal, thus allowing blood volume to increase.…”

“…We propose that, during pregnancy, pregnan alters the transducer properties of the atrial volume receptors, thus allowing blood volume to increase. pregnancy; progesterone; cardiopulmonary receptors; baroreceptors; blood volume PLASMA VOLUME INCREASES PROGRESSIVELY throughout pregnancy, reaching a plateau of 40 -50% above prepregnancy levels by the onset of the third trimester (1,2,4). This increase in circulating volume is one of the earliest and most striking cardiovascular changes observed during pregnancy (12).…”

Pregnancy and the endocrine regulation of the baroreceptor reflex

“…Since then, arterial baroreflex impairment has been documented in several species studied in the conscious state, including dogs (23), rats (24,124), rabbits (21,97,162), goats (152), sheep (104,123), and humans (16,79,122,164,175,193). Reflex responses to atrial stretch are also blunted (51,94,95,103), which may contribute to retention of the expanded blood volume. The depressed baroreflex function observed during normal pregnancy appears to worsen in pregnancy-associated diseases such as preeclampsia (69,129,137,175,195).…”

Paraventricular Neurones Elicit a Volume Expansion‐Like Change of Activity in Sympathetic Nerves to the Heart and Kidney in the Rabbit

“…Thus lesions of the PVN attenuate the renal response to volume load (Lovick et al 1993;Haselton et al 1994). PVN parvocellular neurones exhibit early gene activation following plasma volume expansion (Narvaez et al 1993;Badoer et al 1997) or to stretch of the right atrium (Deng & Kaufman, 1995) and their activity is altered by stimulation of cardiac afferents (Lovick & Coote, 1988a,b, 1989. Activation of PVN neurones alters renal function via the renal nerves (Haselton & Vari, 1998).…”