Role of sex steroid hormones in relative refractoriness to angiotensin II during pregnancy

Relationships between endogenous sex hormone concentrations and vascular function in postmenopausal women

CONTEXT

Differences in postmenopausal endogenous sex hormone concentrations are associated with varying risks of a growing number of common diseases. The relationships between postmenopausal endogenous sex hormone concentrations and vascular function are not well understood.

OBJECTIVE

We examined in postmenopausal women the relationships between endogenous sex hormone concentrations and both blood pressure (BP) and renal vascular resistance (RVR), at baseline and in response to infused angiotensin II (AngII). SUBJECTS, INTERVENTIONS, AND MAIN OUTCOME MEASURES: A total of 34 hypertensive, postmenopausal women were studied in low-sodium and/or high-sodium balance. Serum estradiol, serum progesterone, BP, and RVR were measured at baseline. BP and RVR were remeasured after AngII infusion.

RESULTS

In low-sodium balance, the increases in systolic and diastolic BP in response to infused AngII were blunted with increased serum progesterone concentrations (P < 0.05). The increase in RVR in response to infused AngII was also blunted with increased serum progesterone concentrations (P < 0.005). The relationships between progesterone concentration and vascular response to AngII were independent of age, body mass index, and estradiol concentration. There were no significant correlations between estradiol concentration and BP or RVR response to AngII. There were no significant correlations between sex hormone concentrations and baseline BP or RVR. In high-sodium balance, there were no significant associations between sex hormone concentrations and vascular measures.

CONCLUSIONS

In postmenopausal women in low-sodium balance, the pressor and renovascular responses to AngII are blunted with increased endogenous progesterone concentrations. Our findings suggest a role for endogenous progesterone in modulating vascular function, even within the low postmenopausal range.

Potentiation of the hypotensive effect of adrenomedullin in pregnant rats

The hypotensive effect of adrenomedullin, a potent vasodilator peptide, was examined in conscious pregnant (6, 13 and 20 days of pregnancy) and non-pregnant rats. The intravenous administration of adrenomedullin (0.01-3.0 nmol/kg) produced a dose-dependent depressor response in pregnant and non-pregnant rats. At low doses (0.01-0.1 nmol/kg), the maximum decrease in blood pressure was significantly higher in pregnant rats (20 days pregnant) than in non-pregnant rats. At high doses, no significant difference was observed between the two groups. Furthermore, the administration of adrenomedullin did not significantly affect the basal mean blood pressure (MBP) at any dose when compared to the non-pregnant group at 6 and 13 days of pregnancy. In the ovariectomized rats, the depressor responses in 17beta-estradiol-treated, progesterone-treated and 17beta-estradiol+progesterone-treated rats were not significantly different from that in the control rats, suggesting that the augmented effect on the depressor response to adrenomedullin in pregnant rats may not be due to hormonal changes during pregnancy. The adrenomedullin receptor mRNA level of the descending thoracic aorta was significantly higher in the late-pregnancy rats (20 days of pregnancy). However, the levels did not show any difference between the early-pregnant rats (6 and 13 days of pregnancy) and the non-pregnant rats. These findings suggested that the changes in the depressor response to adrenomedullin which occur at term in pregnant rats may be mediated by changes of adrenomedullin receptor gene expression rather than by sex hormones.

Vascular smooth muscle reactivity to norepinephrine in ovariectomized rats: relationship to vascular PGE2/PGF2 alpha ratio

1. We have recently demonstrated that, in normal female rats, vascular reactivity (VR) and vascular prostaglandin-E2 (PGE2) and prostacyclin production are influenced by the ovarian cycle. 2. In this study, we investigated the vascular reactivity (VR) of isolated rat thoracic aorta to norepinephrine (NE 10(-12)-10(-6)M) in ovariectomized rats (OVX-rats), 48 hr and 8 days after surgical removal of the ovaries and in normally cycling rats (NR) at the proestrus stage of the estrous cycle, when the level of circulating estrogen was higher. 3. In addition, we determined the vascular synthesis of PGE2 and protaglandin-F2 alpha (PGF2 alpha) in both groups of OVX-rats, and in NR during the proestrous stage. 4. The results showed that VR to NE 10(-12)-10(-10) M was similar between OVX-rats and normal rats. 5. However, aortic rings obtained from both groups of OVX-rats showed a significant increase of the contraction response induced by NE 10(-9)-10(-6) M. 6. Furthermore, the contractile response to NE 10(-7)-10(-6) M was greater in the aortic rings from OVX-rats 8 days after ovariectomy compared to OVX-rats 48 hr (p < 0.001). 7. Vascular PGE2 and PGF2 alpha synthesis (ng/mg protein/hr) was significantly higher in both groups of OVX-rats than NR. But the vascular PGF2 alpha synthesis increased more than PGE2 in these OVX-rats, thus the ratio PGE2/PGF2 alpha was decreased significantly in both groups of OVX-rats (p < 0.01 and p < 0.001 OVX-rats 48 hr and 8 days after surgery, respectively) compared to NR-ratio.

Immunocytochemical detection of progesterone receptors. A study in a patient with primary pulmonary hypertension

Primary pulmonary plexogenic arteriopathy (PPPA) is one of the principal conditions in which pulmonary hypertension may be clinically unexpected. It occurs in the lung vessels in the absence of any demonstrable cause. Its high incidence in women of childbearing age combined with reports of disease following delivery of a child or assumption of oral contraceptives suggest that hormonal factors may play a role in the pathogenesis of PPPA. The suspicion that the pulmonary vascular lesions occurring in PPPA could represent the effect of a hormonal mediated vascular hyperreactivity prompted the evaluation of the steroid hormone receptor status on lung tissue obtained from a women suffering from this disease who had a double-lung transplantation. By the immunocytochemical method performed on formalin fixed, paraffin-embedded lung tissue, we showed the presence of progesterone receptors (PR) in the nuclei of the myofibroblasts forming the arterial obstructive intimal proliferations and of the spindle cells present in the walls of the plexiform lesions. To enhance the staining and to facilitate the observation, we used a microwave-based antigen unmasking technique. The lack of estrogen receptors and the presence of PR could have increased, in the case, the sensitivity of the pulmonary muscular arteries to vasoconstrictory compounds. We hypothesize that on this substrate of a presumptive steroid-mediated vasoconstriction the sequence of the histologic lesions characteristic of pulmonary vascular hypertensive disease could have developed.

Systemic and uterine responses to chronic infusion of estradiol-17 beta

Human and ovine pregnancies are associated with increases in plasma levels of estrogens and angiotensin II (ANG II), cardiac output (CO), blood volume (BV), and uterine blood flow (UBF), as well as attenuated ANG II pressor responses. We hypothesized that, in nonpregnant animals, prolonged estradiol-17 beta (E2 beta) treatment would reproduce these endocrine and hemodynamic alterations. Nonpregnant ovariectomized ewes (n = 5) received 5 microgram E2 beta/kg iv followed by 220 micrograms/day for 14 days. Plasma E2 beta increased from 36 +/- 6 to 269 +/- 79 (SE) pg/ml (P < 0.05) during E2 beta treatment, returning to control values 4 days posttreatment. By 3 days of E2 beta, mean arterial pressure (MAP) and systemic vascular resistance (SVR) fell 9 +/- 1 and 29 +/- 1%, whereas heart rate (HR) and CO increased 20 +/- 5 and 26 +/- 1% (P < 0.05). Stroke volume (SV), BV, and plasma volume were unchanged until 7 days of E2 beta, with values rising 17 +/- 5, 13 +/- 3, and 14 +/- 4, respectively (P < 0.05). Although MAP remained similarly depressed (-11 +/- 1%) during week 2 of E2 beta, SVR decreased further (-37 +/- 3%) and was associated with additional increases (P < 0.05) in CO to 44 +/- 5%, reflecting rises in SV (21 +/- 2%) but not HR. Increases in BV correlated with rises in CO (r = 0.55) and SV (r = 0.64) but not HR (r = -0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Lactation affects pressor, volumetric and natriuretic responses to angiotensin II in goats

Demands on cardiovascular function and fluid turnover increase during lactation and pregnancy in the goat, but the hormonal status is different. This study is aimed at investigating the effects of hypertensive angiotensin II (ANGII) in lactating goats. The results were compared with those of pregnancy and control conditions. ANGII (0.5 microgram min-1) was infused intravenously for 60 min (n = 6). The rise in blood pressure in response to ANGII was attenuated during lactation as in pregnancy (P < 0.001 vs control period). ANGII caused reflex bradycardia. Plasma protein concentration decreased by 7.5% during infusions in lactating goats (pregnancy: 9%; control period: 4.5%). Renal Na excretion increased by 260% (lactation), by 400% (pregnancy; n.s. vs. lactation), and by 800% (control period; P < 0.01 vs. lactation). The glomerular filtration rate was unchanged during ANGII infusions in lactating animals, but increased in the other periods. Effective renal plasma flow decreased. ANGII raised aldosterone from < 34.5 pmol l-1 to 539 +/- 80 pmol l-1 (lactation) and to 428 +/- 41 pmol l-1 (control; P < 0.05 vs. lactation), and from 72 +/- 9 to 651 +/- 103 pmol l-1 (pregnancy; P < 0.01 vs. lactation). Plasma progesterone was undetectable during lactation, but varied from 0 to 17 nmol l-1 during control conditions and was 16 +/- 1 nmol l-1 during pregnancy. Oestradiol 17 beta was 181 +/- 22 pmol l-1 in pregnant goats, and undetectable in lactating animals. In conclusion, lactation affects ANGII-induced changes in cardiovascular and fluid regulation, but in this period the effects were not related to progesterone or oestradiol 17 beta.

Neurovascular function during pregnancy in the spontaneously hypertensive rat

1. Blood pressure (BP) declines dramatically in the final week of gestation in the pregnant spontaneously hypertensive rat (SHR). This study investigated the hypothesis that alterations of vascular neuroeffector function in the pregnant SHR and normotensive Wistar-Kyoto (WKY) rat are responsible for this decline. 2. Pregnancy in SHR and WKY rats was associated with a significant drop in BP in the last week of gestation. 3. Responses of the perfused mesenteric vasculature to bolus doses of noradrenaline (NA) and potassium chloride (KCl) were decreased in preparations from SHR rats 4 days before delivery. This decreased responsiveness was absent in preparations from SHR rats 1 day before delivery. Responses of the perfused mesenteric vasculature to sympathetic nerve stimulation were not influenced by pregnancy in the SHR. 4. It is concluded that while there are dynamic changes occurring in neurovascular function just prior to delivery, it is unlikely that they are wholly responsible for the dramatic decline in blood pressure in the SHR rat.

Lack of evidence of a vasodepressor role for relaxin in spontaneously hypertensive and normotensive pregnant rats

To test the possibility that the ovarian polypeptide hormone relaxin mediates the vasodepressor effect of pregnancy, we measured changes in blood pressure in three groups of spontaneously hypertensive and Wistar-Kyoto normotensive rats: (1) pregnant, bilaterally oophorectomized rats on postmating day 13, (2) pregnant, sham-oophorectomized rats on postmating day 13, and (3) nonpregnant, sham-oophorectomized rats after 13 days. The day before parturition we also measured the pressor responsiveness to angiotensin II and norepinephrine. Systolic blood pressure fell significantly during the last week of gestation in both strains, reaching normotensive levels in the hypertensive rats by term. The pressor responsiveness to angiotensin II, but not norepinephrine, of the pregnant rats was reduced compared with that of the nonpregnant rats in both strains. Oophorectomy did not prevent the fall in blood pressure or the decrease in vascular reactivity to angiotensin II. Therefore, although ovarian relaxin secretion increases during pregnancy, it apparently does not decrease vascular sensitivity to angiotensin II or cause vasodilation.

Blood pressure response to angiotensin II in pregnant and lactating goats maintained on high or low sodium intake

Goats were kept on either high (274 mmol day-1) or low (68 mmol day-1) sodium intake during pregnancy, lactation, and anoestrus. High salt (HS) animals had about three times greater renal Na excretion than low salt (LS) animals, but the differences in plasma volume, protein concentration, and haematocrit were generally not significant. Angiotensin II (AII) was infused intravenously for 28-min periods in doses of 0.30, 0.75, or 1.00 nmol min-1. The increase in mean arterial blood pressure (MAP) during AII infusions was greater in HS than in LS goats, but became attenuated in all animals during the course of the pregnancy. In LS goats the MAP rise was smaller in late pregnancy than during lactation and anoestrus. In HS goats the rise in MAP was exaggerated in early pregnancy and was similar to lactation and anoestrus values in late pregnancy. During lactation and anoestrus the goats showed similar MAP increase in response to AII infusions. The pulse pressure was greater during AII infusions performed in early pregnancy, lactation and anoestrus than in late pregnancy. Cardiac arrhythmias were noted during AII infusions, most frequently during lactation and in HS goats in early pregnancy. The results show that a moderately elevated sodium intake causes a significantly higher MAP increase in response to AII infusions during pregnancy. This abolishes the reduction of the MAP increase to AII infusions during late pregnancy as compared to anoestrus; a phenomenon which is observed in goats on a low sodium intake.