The relationship between experimentally determined litter size and maternal blood pressure in spontaneously hypertensive rats

Influence of Swimming Program on the Blood Pressure of Pregnant Hypertensive Rats and Their Fetuses

The hypertension incidence and its complication on pregnant women are growing and can lead to adverse consequences on their fetuses. However, it is known that regular exercise practice can be healthful to hypertensive pregnant women but harmful to fetal growth. So, the objective of this study was to evaluate the effects of exercise beginning before pregnancy or during pregnancy on the maternal blood pressure and reproductive outcome and on the fetal development of spontaneously hypertensive rats (SHR). Pregnant SHR were randomly distributed into three experimental groups: (1) SHR-Control, non-exercised; (2) SHR-Ex0, rats submitted to physical exercise (swimming program) from day zero to 20 of pregnancy; (3) and SHR-ExPr, rats submitted to swimming program before and during pregnancy. At end of pregnancy (day 21), the rats were anesthetized, and reproductive parameters and fetal development were assessed. Blood pressure was reduced at the end of pregnancy in all the groups. Regardless of swimming exposure time, there was reduced maternal weight gain. The exercise decreased fetal weight at term pregnancy, with a higher percentage of small for gestational age (SGA) fetuses and lower number ossification sites, indicating intrauterine growth restriction (IUGR). In conclusion, our findings provide insight to support that swimming exercise in pregnant SHR impairs fetal development, causing IUGR and visceral malformations. Therefore, the indication of physical exercise must be defined very carefully, as it can compromise fetal development.

Analysis of maternal and fetal cardiovascular systems during hyperglycemic pregnancy in the nonobese diabetic mouse

Preconception or gestationally induced diabetes increases morbidities and elevates long-term cardiovascular disease risks in women and their children. Spontaneously hyperglycemic (d)-NOD/ShiLtJ female mice, a type 1 diabetes model, develop bradycardia and hypotension after midpregnancy compared with normoglycemic, age- and gestational day (GD)-matched control (c-NOD) females. We hypothesized that onset of the placental circulation at GD 9-10 and rapid fetal growth from GD 14 correlate with aberrant hemodynamic outcomes in d-NOD females. To develop further gestational time-course correlations between maternal cardiac and renal parameters, high-frequency ultrasonography was applied to d- and c-NOD mice (virgin and at GD 8-16). Cardiac output and left ventricular (LV) mass increased in c-NOD but not in d-NOD mice. Ultrasound and postmortem histopathology showed overall greater LV dilation in d-NOD than in c-NOD mice at mid to late gestation. These changes suggest blunted remodeling and altered functional adaptation of d-NOD hearts. Umbilical cord ultrasounds revealed lower fetal heart rates from GD 12 and lower umbilical flow velocities at GD 14 and GD 16 in d-NOD versus c-NOD pregnancies. From GD 14 to GD 16, d-NOD fetal losses exceeded c-NOD fetal losses. Similar aberrant responses in pregnancies of women with diabetes may elevate postpartum maternal and child cardiovascular risk, particularly if mothers lack adequate prenatal care or have poor glycemic control during gestation.

Maternal adaptation in pregnant hypertensive rats: improvement of vascular and inflammatory variables and oxidative damage in the kidney

BACKGROUND

Mechanisms of normalization of blood pressure in spontaneously hypertensive rats (SHR) during pregnancy were investigated. We hypothesized that at the end of pregnancy (20th day), the modified renal renin-angiotensin system (RAS) plays a pivotal role in this effect associated with reduced inflammation and oxidative damage.

METHODS

We measured blood pressure and heart rate (HR) using a noninvasive tail-cuff method in conscious SHR and Wistar Kyoto rats (WKY). Nonpregnant (-NP) or pregnant (-P) SHR and WKY were used to compare the changes of angiotensin II (ANG II) type 1 (AT1) and type 2 (AT2) receptor expression in the kidney. Renal modification of proinflammatory enzyme expression, cyclooxygenase-2 (COX-2), and inducible nitric oxide synthase (iNOS) and their transcription factor nuclear factor-kappaB (NF-kappaB) were also evaluated. Renal malonyldialdehyde (MDA) content and protein nitrotyrosylation, as indicators of oxidative stress, were assessed. Moreover monocyte chemotactic protein-1 (MCP-1) mRNA was determined.

RESULTS

Our findings indicate that the significant reduction of blood pressure induced by pregnancy in the SHR strain could be related to reduced AT1 and increased AT2 expression. We also saw a significant decline in renal NF-kappaB, COX-2, iNOS, and macrophage infiltration, as well as the fall in oxidative stress indicators.

CONCLUSIONS

The increased proinflammatory and oxidative variables, seen in SHR, are strongly ameliorated by pregnancy. In pregnant SHR animals, the adaptive and compensative changes of RAS and inflammation in the kidney seem to contribute to the reduction of blood pressure near term.

Evaluation of placental protein modifications in normotensive and spontaneously hypertensive rats

Hypertension in pregnancy is often associated to placental deficiency. Therefore several physiopathological modifications occur to sustain fetal well-being through protective mechanisms. Here, we used spontaneously hypertensive rat (SHR) and normotensive Wistar-Kyoto (WKY) counterpart to evaluate in late gestation (d 20) modification of placental proteins involved in adaptation to hypertension. Placenta from WKY and SHR was excised for the evaluation of protein changes by Western blot analysis and zymography. In particular, we showed in SHR placentas an increase in angiotensin receptor type 1 and a decrease in angiotensin converting enzyme. Conversely, inducible nitric oxide synthase expression was increased, while constitutive endothelial nitric oxide synthase was similar in both groups. Placentas from SHR showed a reduced protein expression in both peroxisome proliferators-activated receptors-alpha and -gamma. Pro-metalloproteinase-9 activity was not significantly modified, whereas both pro-metalloproteinase-2 and its active form present a higher activity in SHR placentas. Moreover, at the end of pregnancy, cyclooxygenase-2 expression decreased in SHR placentas. These data may provide new insights into the placental adaptive mechanisms that take place during pregnancy in SHR.

Effects of L-arginine oral supplements in pregnant spontaneously hypertensive rats

PURPOSE: To evaluate the effects of L-arginine oral supplementation in spontaneously hypertensive pregnant rats (SHR). METHODS: Thirty SHR and ten Wistar-EPM-1 virgin female rats were used in the study. Before randomization, females were caged with males of the same strain (3:1). Pregnancy was confirmed by sperm-positive vaginal smear (Day 0). Wistar-EPM-1 rats served as counterpart control (C-1). SHR rats were randomized in 4 groups (n=10): Group Control 2, non-treated rats; Group L-Arginine treated with L-arginine 2%; Group Alpha-methyldopa treated with Alpha-methyldopa 33mg/Kg; Group L-Arginine+Alpha-methyldopa treated with L-arginine 2%+Alpha-methyldopa 33mg/Kg. L-arginine 2% solution was offered ad libitum in drinking water and Alpha-methyldopa was administered by gavage twice a day during the length of pregnancy (20 days). Blood pressure was measured by tailcuff plethysmography on days 0 and 20. Body weight was measured on days 0, 10 and 20. Results were expressed as mean ± SD (Standard Deviation). One-Way ANOVA/Tukey (or Kruskal-Wallis/Dunn, as appropriate) was used for group comparisons. Statistical significance was accepted as p<0.05. RESULTS: There was no significant weight gain in isolated L-arginine treated SHR. Mean blood pressure decreased in L-arginine-treated SLR compared with untreated-SHR rats. CONCLUSION: L-arginine oral supplementation reduces blood pressure in spontaneously hypertensive rats during pregnancy.

Possible involvement of aminopeptidase A in hypertension in spontaneously hypertensive rats (SHRs) and change of refractoriness in response to angiotensin II in pregnant SHRs

BACKGROUND

Hypertension complicated with pregnancy is a major cause of maternal and fetal mortality, but its pathophysiology is unclear.

OBJECTIVE

To investigate the pressor response to angiotensin II (Ang II) and the involvement of the Ang II degrading protease, aminopeptidase A, in spontaneously hypertensive rats (SHRs).

DESIGN

Pregnant SHRs and Wistar-Kyoto (WKY) rats were studied. Angiotensin II (200 ng/kg per min) or saline was infused by osmotic pump from day of 15 gestation, and caesarean section was performed at day 20 of gestation. Blood pressure during pregnancy, weight of placentas and pups at caesarean section, and aminopeptidase A activity in placenta and renal cortex were measured.

RESULTS

Ang II treatment induced increases in blood pressure that were greater in non-pregnant WKY rats than those in pregnant WKY rats, pregnant SHRs, and non-pregnant SHRs. Renal aminopeptidase A activity in SHRs was significantly lower than that in WKY rats. Renal aminopeptidase A activity in pregnant SHRs was significantly greater than that in non-pregnant SHRs, but there was no significant increase in pregnant WKY rats. Placental aminopeptidase A activity in SHRs was greater than that in WKY rats. Placental aminopeptidase A activity in WKY rats was increased by Ang II, but was not increased in SHRs. Weights of placentas and pups were significantly lower in SHRs than in WKY rats.

CONCLUSIONS

Renal aminopeptidase A may be involved in the development of hypertension and the regulation of blood pressure in SHRs. Placental aminopeptidase A may be upregulated in response to fetal stress in pregnant SHRs.

Effects of hypertension on maternal adaptations to pregnancy: experimental study on spontaneously hypertensive rats

CONTEXT

Animal models for essential hypertension have been used for understanding the human pathological conditions observed in pregnant hypertensive women.

OBJECTIVE

To study the possible effects of pregnancy on hypertension and of hypertension on pregnancy in spontaneously hypertensive rats (SHR), and in their normotensive Wistar-Kyoto (WKY) counterparts.

TYPE OF STUDY

Comparative study using laboratory animals.

SETTING

Animal Research Laboratory of Clinical Medicine at the Medical School of Botucatu, São Paulo State University, Brazil.

SAMPLE

Ten to twelve-week-old virgin female normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). The animals were separated into four groups: 15 pregnant spontaneously hypertensive rats (SHR-P), 10 non-pregnant spontaneously hypertensive rats (SHR-NP), 15 pregnant normotensive rats (WKY-P), and 10 non-pregnant normotensive rats (WKY-NP).

MAIN MEASUREMENTS

The blood pressure was evaluated by the tail cuff method, in rats either with or without prior training for the handling necessary for tail cuff measurements. The maternal volume expansion was indirectly evaluated by weight gain, and by systemic parameters as hematocrit, hemoglobin, total protein, albumin and sodium retention. The perinatal outcome of pregnancy was evaluated by analysis of resorptions, litter size, rate of low weight and number of stillbirths.

RESULTS

The late fall in blood pressure in the pregnant SHR strain and in the normotensive WKY strain can only be detected in rats previously trained to accept the handling necessary for the tail cuff measurement. During pregnancy the body weight gain was significantly higher in WKY than in SHR rats. Systemic parameters were significantly lower in pregnant WKY rats than in non-pregnant WKY rats, while no differences were observed between pregnant and non-pregnant SHR groups. In pregnant WKY rats the sodium retention was higher from the 13th day onwards, while in SHR rats this occurred only on the 21st day. The characteristics of reproductive function such as number and weight of fetus, perinatal mortality and the resorption rate were significantly affected in the SHR strain.

CONCLUSION

The SHR strain may be considered as a model for chronic hypovolemic maternal hypertension, with the fetal growth retardation being determined by this hypovolemic state.

Effect of cardiac receptor stimulation on renal vascular resistance in the pregnant rat

Stimulation of cardiac receptors (CR) evokes blunted reflex reductions in mean arterial pressure (MAP) in pregnant compared with virgin rats. Because CR-mediated sympathoinhibition has preferential effects on the kidney, we tested whether, during pregnancy, renal vascular resistance (RVR) changes less in response to CR stimulation and investigated possible mechanisms. MAP, right atrial pressure, renal sympathetic nerve activity (RSNA), renal blood flow (RBF), and RVR were measured in anesthetized animals in response to CR stimulation by graded atrial injections of saline. Baseline MAP and RVR and reflex changes in these variables during CR stimulation were reduced in late-pregnant vs. virgin rats (P<0.05). Reflex changes in RSNA were attenuated in pregnant rats, but changes in RBF as a function of RSNA were similar in both groups. ANG II AT(1)-receptor blockade increased basal RBF more in virgin rats (P<0.05), but between-group differences in reflex changes in MAP, RSNA, and RVR were maintained after AT(1) blockade. Thus during CR simulation, reflex changes in RVR were reduced in pregnant versus virgin rats. This difference does not appear to involve differential effects of ANG II.

Pregnancy and steroid hormones enhance the vasodilation responses to CGRP in rats

We recently reported that calcitonin gene-related peptide (CGRP) reversed the hypertension induced by nitric oxide inhibition in pregnant rats and that this effect appeared to be progesterone dependent. In the present study, we examined whether the vasodilator responses to CGRP are increased during pregnancy and whether these responses are steroid hormone dependent. Three groups of ovariectomized (Ovx) rats (n = 4-8 rats/group) were studied 3 days after daily treatment (subcutaneous injection) with progesterone (P; 2 mg/injection, twice daily for 3 days, in 0.2 ml of sesame oil), 17beta-estradiol (E; 2.5 microgram/injection, twice daily for 3 days, in 0.2 ml of sesame oil), or vehicle (sesame oil). A fourth group (n = 6 rats) of pregnant rats was studied on day 19 of gestation. A fifth group of adult, nonpregnant rats (n = 6 rats), regardless of stage of estrous cycle, was also used in this study. Mean arterial blood pressure (MAP) was continuously monitored in fully awake and free-moving instrumented rats. MAP was measured before and after administration of either saline or varying bolus doses of CGRP (9-360 pmol/kg body wt). CGRP produced a dose-dependent decrease in MAP in all rats with a significant (P < 0.05) reduction in MAP beginning with a CGRP dose of 90 pmol/kg and with maximal effects observed at 360 pmol/kg. Decreases in MAP in response to CGRP were significantly (P < 0.05) greater in pregnant compared with nonpregnant rats. Similarly to pregnant rats, Ovx rats given both E and P treatments produced greater decreases in MAP in response to CGRP at 90, 180, and 360 pmol/kg doses compared with both ovary-intact and Ovx nonpregnant rats, which were not different from each other. In summary, these data show that 1) the hypotensive effects of CGRP are dose dependent and 2) the hypotensive effects of CGRP are enhanced during pregnancy and in Ovx rats treated with either E or P. Therefore, we suggest that the decrease in vascular tone that is seen during pregnancy may be mediated, at least in part, by a sex steroid hormone-induced increase in the vascular sensitivity to the vasodilator effects of CGRP.

Perinatal growth disturbance in the spontaneously hypertensive rat

Disproportionate fetal and placental growth are associated with the development of hypertension in the rat and human. Here we report differences in fetal, neonatal, and placental growth, and in metabolism and endocrinology, between the spontaneously hypertensive rat (SHR), a genetic model for human essential hypertension, and the control Wistar-Kyoto (WKY) strain. Gestation in SHR (23 d) was longer than in WKY by 20 h. Body weights were lower in the SHR from fetal d 16 to 20 and on postnatal d 15. However, on fetal d 22 and postnatal d 1, there was no significant difference in body weight between SHR and WKY. SHR placentas were larger than those of WKY at d 20, and by term there was a difference of 30% (p < 0.01). Other indices of disproportionate growth were hypertrophy of the fetal heart and kidney and decreased ponderal index in the SHR neonate. Blood glucose in SHR fetuses was lower than in WKY fetuses (p < 0.05), whereas blood lactate was higher (p < 0.05) and fetal hematocrit was reduced (p < 0.001). These findings suggest undernutrition and placental insufficiency may occur in SHR fetuses. Plasma IGF-II was increased on the last day of gestation in both strains, whereas IGF-I was unaltered. Fetal liver IGFBP-2 mRNA and plasma IGFBP-2 levels were reduced in SHR on fetal d 20 and 22 (p < 0.01). Differences in growth and endocrine and metabolic parameters suggest abnormal perinatal physiology in the SHR, which may influence the later development of hypertension.

Glomerular hemodynamic responses to pregnancy in rats with severe reduction of renal mass

These studies investigate glomerular hemodynamic responses to pregnancy in rats with 5/6th reduction of renal mass of four weeks duration. Both preglomerular and efferent arteriolar resistances (RA and RE) fell significantly at midterm although single nephron glomerular filtration rate (SNGFR) and glomerular plasma flow (QA) were unchanged versus virgins. In late pregnant rats with reduction of renal mass, the gestational fall in RA and RE was maintained and GFR, RPF, SNGFR and QA were higher compared to virgins. The gestational renal vasodilation was prolonged in this model of hypertension versus normals and a peripheral vasodilation is also indicated by the late fall in blood pressure. In virgins with 5/6th reduction of renal mass, PGC is elevated but in pregnant rats PGC fell towards term. The value of Kf was doubled in late pregnancy compared to virgins. All three groups of rats with reduction of renal mass showed similar proteinuria and similar levels of focal glomerular sclerosis, suggesting that pregnancy did not exacerbate the glomerular damage in this model of hypertension and renal disease. A decrease in hematocrit in late pregnancy compared with both virgin and midterm pregnancy indicated a plasma volume expansion. We conclude that when superimposed on hypertension with glomerular damage due to 5/6th reduction of renal mass, pregnancy induced gestational renal and peripheral vasodilation and plasma volume expansion. Since pregnancy was antihypertensive and lowered PGC, there was no hemodynamic basis for pregnancy-associated exacerbation of damage in this model of glomerular injury.

Endothelium-derived relaxing factor inhibition augments vascular angiotensin II reactivity in the pregnant rat hind limb

OBJECTIVE

The purpose of our study was to determine whether endothelium-derived relaxing factor plays a role in the blunting of maternal vascular reactivity in pregnancy.

STUDY DESIGN

We measured the concentration-pressor responses to norepinephrine (10(-8) to 10(-4) mol/L and angiotensin II (10(-10) to 10(-6) mol/L) in isolated, perfused hind limbs of nonpregnant and pregnant (postmating day 20 to 21) normotensive Wistar-Kyoto and spontaneously hypertensive rats. The hind limbs were perfused at 4 ml/min with Krebs-Ringer solution containing indomethacin (10(-5) mol/L to inhibit prostaglandin production and were either infused with N omega-monomethyl-L-arginine (10(-4) mol/L), a specific inhibitor of endothelium-derived relaxing factor synthesis, or 0.9% saline solution (untreated).

RESULTS

Baseline perfusion pressure was similar in the nonpregnant and pregnant hind limbs of both strains, and N omega-monomethyl-L-arginine had no effect on perfusion pressure. Norepinephrine induced similar pressor responses in the nonpregnant and pregnant hind limbs of both strains, and N omega-monomethyl-L-arginine did not alter these responses. Angiotensin II pressor responses were significantly attenuated in the pregnant rat hind limbs compared with the nonpregnant rat hind limbs. N omega-monomethyl-L-arginine enhanced the angiotensin II responses in the pregnant, but not in the nonpregnant, rat hind limbs.

CONCLUSION

The results suggest that rat pregnancy is not associated with generalized refractoriness to all vasoconstrictors and that endothelium-derived relaxing factor plays a role in attenuating vascular reactivity to angiotensin II.

Nature/nurture and the nature of nurture in the etiology of hypertension

Four reviews on the the role of developmental factors in hypertension are introduced and set in historical context. Recent research in the laboratory rat has shown that the preweaning environment makes an important contribution to the level of blood-pressure reached in adult life in genetic models of hypertension. Both of the most commonly used models of hypertension, the SHR and SS/Jr rat strains, exhibit lower BP in adult life, if they are fostered shortly after birth to mothers from their normotensive control strains. It has been suggested that it is the idiosyncratic maternal behavior of the hypertensive mothers which contributes to the elevated BP of their offspring, and it has been amply demonstrated that there is an association between a constellation of behaviors emitted by rat mothers and the adult BP of their offspring in a wide variety of genetic groups (inbred hypertensive animals, F1's and F2's). In addition to the above, maternal environment has been demonstrated to have a significant impact on the pathophysiological response of hypertensive animals to a high salt diet. Being raised by an SHR mother, versus an SS/Jr mother, increases the magnitude of BP increases to a high salt diet, susceptibility to hemorrhagic stroke, body weight loss and the risk of mortality. A variety of physiological systems are undergoing rapid change during the preweaning period and may mediate the effects of differences in the maternal environment. These include the renin-angiotensin system and the peripheral sympathetic nervous system. Nutritional factors may be involved in all of the phenomena referred to above. Thus, any physiological mechanisms that are proposed to link maternal behavior to its effects on the physiology of adult animals should recognize the involvement of nutritional factors. Research on the role of developmental factors such as maternal behavior in genetic models of hypertension is at the interface of two growing disciplines: behavior genetics and developmental psychobiology. The methodological and conceptual contributions of these fields to advancing our understanding of these phenomena is emphasized.

Enhanced endothelium-derived relaxing factor activity in pregnant, spontaneously hypertensive rats

Pregnancy is normally associated with vasodilation that, in hypertensive animals such as the spontaneously hypertensive rat, causes a profound decrease in blood pressure. To test the possibility that enhanced basal endothelium-derived relaxing factor activity has a role in the vasodilation of pregnancy, we measured the changes in mean arterial pressure and heart rate induced by NG-monomethyl-L-arginine, a specific inhibitor of endothelium-derived relaxing factor synthesis, in conscious nonpregnant and pregnant (postmating day 20 to 21) normotensive Wistar-Kyoto and spontaneously hypertensive rats. NG-monomethyl-L-arginine caused similar dose-dependent increases in mean arterial pressure in nonpregnant and pregnant Wistar-Kyoto rats, but the accompanying decrease in heart rate was significantly greater in nonpregnant rats than in pregnant ones. In the spontaneously hypertensive rats, NG-monomethyl-L-arginine caused significantly greater dose-dependent increases in mean arterial pressure in pregnant compared with nonpregnant rats; there were no differences in the decreases in heart rate. These pressor responses were partially reversed by excess L-arginine but not D-arginine. Indomethacin had no effect on the pressor response to NG-monomethyl-L-arginine or the depressor response to L-arginine after NG-monomethyl-L-arginine. Therefore basal endothelium-derived relaxing factor plays a role in vascular tone and blood pressure regulation in vivo, and pregnancy may be associated with enhanced basal endothelium-derived relaxing factor activity in the hypertensive spontaneously hypertensive rats.

Circadian rhythms of heart rate and mean arterial pressure in chronically instrumented pregnant rats

With the use of a chronic preparation to directly monitor blood pressure and heart rate in pregnant rats, continuous data were obtained over the last half of gestation in normotensive rats. Over this time span, the animals showed significant decreases in blood pressure and increases in heart rate. Heart rate exhibited marked and consistent circadian rhythmicity with peaks occurring near the midportion of the dark phase of the 24-hour cycle. Blood pressure rhythms were less prominent and peaked later. The trends observed in blood pressure and heart rate over gestation suggest that the pregnant rat is a useful model for studying the cardiovascular effects of pregnancy.

Maternal and uteroplacental hemodynamic effects of chronic captopril in the hypertensive, term-pregnant rat

The chronic effects of captopril on maternal hemodynamics and organ perfusion were investigated in 10 untreated and 10 captopril-treated pregnant spontaneously hypertensive rats by means of the radioactive-labeled microsphere technique. The normal decrease in blood pressure during gestation was prevented by reduction of litter size to two conceptuses on day 7 of gestation. Captopril (approximately 10 mg/kg/day) or drug vehicle (50% ethyl alcohol) was administered intraperitoneally by an osmotic pump from day 7 to 21. At term mean arterial pressure was 23% lower in the captopril-treated group as the result of a 29% decrease in total peripheral resistance without a significant change in cardiac output. The decrease in total peripheral resistance was primarily caused by a decline in splanchnic and skin resistances. Maternal organ and uteroplacental perfusion were not significantly altered. We conclude that administration of captopril during the last 2 weeks of pregnancy in the hypertensive rat effectively lowers maternal blood pressure without adverse effects on organ and uteroplacental perfusion.