Plasma Concentrations of Atrial Natriuretic Factor and Hemodynamics in Pregnancy-Induced Hypertension

Abstract

Plasma values of atrial natriuretic factor (ANF) were evaluated in 31 women with pregnancy-induced hypertension (PIH) and 31 normal pregnant women at the same age of gestation. In 27 women with PIH and 27 normal pregnant women forearm venous tone (FVT) was evaluated by Strain Gauge Plethysmography. Forearm vascular resistance (FVR) was measured as the ratio of mean blood pressure (MBP) to forearm blood flow. In addition Cardiac Index (CI) by means of transthoracic electrical bioimpedance and total peripheral vascular resistance (TPR) (with the Frank Equation) were also measured. In comparison with the normal pregnant women, the women with PIH had similar values of hematocrit (as an index of plasma volume) and significantly higher levels of FVR and TPR, while ANF plasma values did not differ significantly. Subdividing the women with PIH in relation to the presence of proteinuria (greater than or equal to 0.3 g/l), those with proteinuria, in addition to significantly higher levels of FVR and TPR, had significantly higher levels of FVT than normal pregnant women, while ANF plasma values were higher even though the difference was only near the level of significance. Hypertensive women with proteinuria also had higher values of FVT than hypertensive women without proteinuria. By means of multiple regression ANF did not show any significant correlations with hematocrit or sodium excretion. Hypertension with proteinuria seems to represent a more severe form of the disease in which, in addition to the probable influence of other factors such as the renin-angiotensin and prostaglandin systems, a greater increase in peripheral sympathetic tone than in hypertension alone appears to be present, causing a reduction in venous compliance in addition to the elevation in FVR and TPR, with increase in central blood volume and atrial stretch. This may explain the higher ANF plasma levels in these patients in comparison with normal pregnant women, even though the absence of a significant correlation of ANF with hematocrit and the fact that ANF increase was only near the level of significance may suggest a change in the relation between ANF secretion and atrial volume receptors in pregnancy either normal or complicated by hypertension. ANF does not seem to play an important role in water and sodium excretion in PIH probably because of the presence of very high plasma levels of hormones such as aldosterone, progesterone and oestriol which, together with renal prostaglandins, seem to be involved in diuresis and natriuresis in pregnancy.

Peripartal Temporal Course of Endothelin 1, Angiotensin II, and Atrial Natriuretic Peptide in Pre-Eclampsia and Normotensive Pregnancy

“…In the hypertensive pregnant women elevated ANP-levels were found over the whole observation period. This is in accordance with previous studies [13][14][15][16]. The increased ANP levels are most probably due to an increased secretion, since metabolic clearance is normal [1].…”

“…It is synthesized in the myocardiocytes of the mammalian heart, and there are findings suggesting that it is also produced in astrocytes and neurons of the human brain [23,24]. In patients with pre-eclampsia ANP levels are commonly elevated [13][14][15][16]. However, its pathophysiological role is still not fully understood.…”

Hypertension in pregnancy

“…147 Their forearm vascular resistance and tone are higher than those recorded in women with GH. 150 What factors might be driving these changes? Ambulatory blood pressure monitoring shows that in normal pregnant women, as in the non-pregnant state, the blood pressure falls at night, but in women with PE, this fall is blunted, 151 and even reversed in ෂ20%.…”