Hypertension control in two Canadian communities: evidence for better treatment and overlabelling

Relative contribution of the prenatal versus postnatal period on development of hypertension and growth rate of the spontaneously hypertensive rat

1. To determine the relative roles of the prenatal and postnatal (preweaning) environment on the development of blood pressure and growth rate in the spontaneously hypertensive rat (SHR) of the Okamoto strain, we used combined embryo transfer and cross-fostering techniques between SHR and normotensive Wistar-Kyoto (WKY) rats to produce offspring whose development was examined during the first 20 weeks of life. 2. We measured litter sizes, bodyweights and tail-cuff blood pressures in offspring at 4, 8, 12 and 20 weeks of age. We also recorded heart, kidney and adrenal weights at 20 weeks of age, when the study concluded. 3. We found that both the in utero and postnatal environments provided by the SHR mother could significantly affect WKY rat offspring growth rates, but blood pressure was unaffected in this strain. In SHR offspring, the SHR maternal in utero and suckling period both contributed to the rate of blood pressure development in the SHR, but not the final blood pressure of offspring at 20 weeks of age. This effect was greater for male than female offspring. Organ weights were largely unaffected by the perinatal environment in either strain. 4. We conclude that although the SHR maternal in utero and immediate postnatal environment both contribute to the rate of blood pressure development in the SHR, they do not appear to contribute to the final blood pressure of offspring at maturity. The SHR maternal environment also alters growth rate that may, in turn, underlie these effects on SHR blood pressure development, particularly in males.

Reduced fetal, placental, and amniotic fluid PTHrP in the growth-restricted spontaneously hypertensive rat

Evidence implicates pivotal roles for parathyroid hormone-related protein (PTHrP) in stimulating cell growth and differentiation, placental calcium transport, and placental vasodilatation. As spontaneously hypertensive rat (SHR) fetuses are growth restricted compared with those of its normotensive control, the Wistar Kyoto (WKY) rat, we examined intrauterine PTHrP and total and ionic calcium concentrations in these rats. Fetal plasma PTHrP concentrations, but not total calcium concentrations, were lower in the SHR compared with WKY (P < 0.05). SHR placental concentrations of PTHrP were lower than in WKY (P < 0.03) and failed to show the increase observed in WKY near term (P < 0.05). PTHrP concentrations in amniotic fluid from SHR were not raised near term and were lower compared with WKY (P < 0.0005). The increased ionic calcium concentrations in amniotic fluid in the WKY near term (P < 0.05) were not detected in the SHR. Thus SHR fetal plasma, placental, and amniotic fluid PTHrP concentrations were reduced and associated with fetal growth restriction. We suggest that PTHrP may play a role in the etiology of both growth restriction during pregnancy and hypertension later in life.

Fetal versus maternal determinants of the reduced fetal and placental growth in spontaneously hypertensive rats

OBJECTIVE

Epidemiological studies indicate that a reduced birth weight and enlarged placenta increase the likelihood of human cardiovascular disease later in life. The relative importance of fetal versus maternal factors in these phenomena is not known. To assess the relative role of genotypic versus environmental factors in this effect, we examined whether the altered fetal and placental growth rates and amniotic fluid volume of spontaneously hypertensive rat (SHR) fetuses of the Okamoto strain, are modified by gestation in normotensive Wistar- Kyoto (WKY) rat mothers and vice versa.

DESIGN

One-day-old SHR embryos were gestated for 16 days in either SHR or WKY recipients. Similarly, 1-day-old WKY rat embryos were gestated for 16 days in either SHR or WKY surrogates. At 16 days, fetal and placental weights were recorded. Paternal and maternal donor and recipient blood pressures, maternal body weight and average litter size within the four groups were also studied.

METHODS

One cell SHR and WKY embryos were harvested from timed matings and transferred to psuedopregnant mothers of the same or opposite strain. Timed matings required routine vaginal smears for the detection of proestrus and the presence of sperm following overnight matings. Harvested embryos were temporarily maintained in culture medium in a 37 degrees C incubator until injection into the oviduct of recipients. Blood pressures were meaured using indirect tail-cuff plethysmography and a computerized data acquisition system.

RESULTS

SHR fetal and placental weights at 16 days gestation were significantly lower than WKY fetal and placental weights, irrespective of maternal strain. At 16 days of gestation, the fetal and placental weights of SHR fetuses gestated in WKY rat surrogate mothers (0.21 +/- 0.01 g and 0.19 +/- 0.01 g, respectively) were not significantly different from those of SHR gestated in a surrogate SHR mother (0.21 +/- 0.01 g and 0.18 +/- 0.01 g, respectively). Similarly, the fetal and placental weights of WKY fetuses gestated in a WKY rat (0.27 +/- 0.01 g and 0.25 +/- 0.01 g, respectively) were unaltered by gestation in a SHR recipient (0.25 +/- 0.01 g and 0.23 +/- 0.01 g, respectively). The amniotic fluid volumes of SHR gestated in WKY rats and those of WKY fetuses gestated in SHR were not significantly different to each other (0.37 +/- 0.01 ml versus 0.38 +/- 0.01 ml, respectively) and were intermediate between the values for SHR and WKY fetuses gestated in a mother of the same strain (0.34 +/- 0.01 ml versus 0.44 +/- 0.02 ml, respectively).

CONCLUSION

The SHR fetus exhibited reduced growth rate and placental size irrespective of maternal surrogate strain, suggesting that these measures are likely to be determined by the fetus or the placenta and, presumably, are independent of maternal blood pressure or altered electrolyte and hormonal milieu.

Adrenocortical activity in fetal SHR and WKY rats

There is increasing evidence that the intrauterine milieu and corticosteroid exposure play a role in the etiology of hypertension. We examined adrenocortical gene expression and circulating corticosteroids in the d 21 fetal spontaneously hypertensive rat (SHR) and its normotensive genetic control, the Wistar-Kyoto (WKY) rat. By RNase protection assays, we found no differences in the relative abundances of mRNAs for P450scc and P450c11beta, and barely detectable P450c11AS mRNA in the adrenals of fetal SHR and WKY rats. P450c11B3 RNA was undetectable by reverse transcription polymerase chain reaction in both SHR and WKY fetuses. The zonal expression of P450c11 mRNA was comparable in SHR and WKY fetuses by in situ hybridization histochemistry. There were no significant differences in peripheral levels of aldosterone and corticosterone by radioimmunoassay in fetal SHR and WKY rats. Based upon the absence of distinct differences in the aspects of adrenocortical activity examined, it is unlikely that they are integral in the programming of hypertension in this model.

Ontogenetic aspects of hypertension development: analysis in the rat

In this review, we attempt to outline the age-dependent interactions of principal systems controlling the structure and function of the cardiovascular system in immature rats developing hypertension. We focus our attention on the cardiovascular effects of various pharmacological, nutritional, and behavioral interventions applied at different stages of ontogeny. Several distinct critical periods (developmental windows), in which particular stimuli affect the further development of the cardiovascular phenotype, are specified in the rat. It is evident that short-term transient treatment of genetically hypertensive rats with certain antihypertensive drugs in prepuberty and puberty (at the age of 4-10 wk) has long-term beneficial effects on further development of their cardiovascular apparatus. This juvenile critical period coincides with the period of high susceptibility to the hypertensive effects of increased salt intake. If the hypertensive process develops after this critical period (due to early antihypertensive treatment or late administration of certain hypertensive stimuli, e.g., high salt intake), blood pressure elevation, cardiovascular hypertrophy, connective tissue accumulation, and end-organ damage are considerably attenuated compared with rats developing hypertension during the juvenile critical period. As far as the role of various electrolytes in blood pressure modulation is concerned, prohypertensive effects of dietary Na+ and antihypertensive effects of dietary Ca2+ are enhanced in immature animals, whereas vascular protective and antihypertensive effects of dietary K+ are almost independent of age. At a given level of dietary electrolyte intake, the balance between dietary carbohydrate and fat intake can modify blood pressure even in rats with established hypertension, but dietary protein intake affects the blood pressure development in immature animals only. Dietary protein restriction during gestation, as well as altered mother-offspring interactions in the suckling period, might have important long-term hypertensive consequences. The critical periods (developmental windows) should be respected in the future pharmacological or gene therapy of human hypertension.

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.

Patient education for the millennium: beyond control and emancipation?

This paper reports on a study carried out in Nottinghamshire, UK, which focused upon patient education for low back pain in general (family) practice. This study found that patient education could not be viewed simply as either a repressive social control mechanism or as a vehicle for patient empowerment and social change. The paper suggests that a new theoretical and practical orientation to patient education is required which transcends binary categorizations. The existing control/empowerment dichotomy offers a persuasive, yet restrictive conceptualization of patient education which has created rival camps of theoreticians and practitioners intent on demonizing each other. In the light of presented findings, the study suggests a new trajectory for patient education focusing on local possibilities for change.

Altered uterine environment in the spontaneously hypertensive rat

1. In order to determine the role of the uterine environment in the development of hypertension in the spontaneously hypertensive rat (SHR) we examined the patterns of fetal and placental growth and the composition of amniotic fluid of SHR and normotensive Wistar-Kyoto (WKY) rats during the final trimester of pregnancy. 2. SHR and WKY embryos and amniotic fluid were collected at days 15 and 20 of pregnancy, and fetal and placental weight and amniotic fluid volume were recorded. The sodium and potassium concentration of amniotic fluid was also measured. 3. Fetal and placental weights were significantly lower in SHR compared to WKY at 15 and 20 days of gestation. Amniotic fluid volume was significantly lower in SHR at 15 days, but significantly higher at 20 days. Amniotic fluid sodium concentration was significantly lower in SHR at 15 days but not different at 20 days when compared to WKY. Potassium concentration was lower in SHR at both ages. 4. Thus the reduced placental weight early in the gestational period of the SHR may play a role in its underdevelopment in utero and hence its reduced birthweight. The SHR foetus is also bathed in a hypokalaemic amniotic fluid of increased volume. How this might influence fetal development and later blood pressure is unclear. Also whether these changes are of maternal or fetal origin remain to be determined.

Role of uterine factors in the development of hypertension in SHR

1. To examine whether the uterine environment plays a role in the development of hypertension in the spontaneously hypertensive rats (SHR), we have compared fetal weight, placental weight, and amniotic fluid composition of SHR and Wistar-Kyoto (WKY) rats after 20 days of gestation. 2. Pregnant SHR and WKY were anaesthetized at 20 days of gestation and the uterus and embryonic sacs removed. Fetal and placental weights were recorded and amniotic fluid collected for measurement of volume, osmolality and electrolyte composition. 3. No significant difference was found in litter size and placental weight between SHR and WKY. Total embryonic sac weight and fetal weight of SHR were significantly lower than WKY. Amniotic fluid volume, sodium concentration and osmolality of SHR were significantly higher than WKY, while amniotic fluid potassium concentration of SHR was significantly lower than WKY. 4. Thus, the SHR foetus was significantly underweight compared to the WKY and was bathed in amniotic fluid with a significantly higher osmolality and sodium concentration. As the mature foetus is known to drink amniotic fluid, it is hypothesized that the elevated Na/K ratio in SHR amniotic fluid may instigate or accelerate the hypertensive process.

Some problems in applying evidence in clinical practice

There is a considerable gap between sound evidence concerning health care interventions and the services that patients actually receive as health care. Practitioners and the health care system must overcome a number of barriers to narrow the gap. Viewed simplistically, there are three steps from evidence to practice: getting the evidence straight; developing clinical practice guidelines that are faithful to both the evidence and the clinical and personal situations of patients; and applying these guidelines to the right patient at the right time in the right way. Special problems in getting the evidence straight stem from difficulties in finding sound evidence. Lack of agreement on evidence standards undermine the effectiveness of authoritative practice guidelines. Applying evidence and practice guidelines effectively and efficiently is often thwarted by mismatches between evidence and usual practice circumstances. Time pressures undermine interpretation and application of evidence at every step. Understanding these problems may permit development of more effective strategies to bridge the gap between evidence and practice.