Spontaneously Hypertensive Rats Pups Research Articles

Altering Early Life Gut Microbiota Has Long-Term Effect on Immune System and Hypertension in Spontaneously Hypertensive Rats.

Hypertension is regulated by immunological components. Spontaneously hypertensive rats (SHR) display a large population of proinflammatory CD161 + immune cells. We investigated the effect of early post-natal gut microbiota on the development of the immune system and resulting hypertension in the SHR. We first examined the microbial populations in the fecal samples of SHR and normotensive control WKY using 16S rDNA sequencing. We found that in the newborn SHR (1-week old) the gut microbiota was qualitatively and quantitatively different from the newborns of normotensive WKY. The representation of the predominant bacterial phylum Proteobacteria was significantly less in 1-week old SHR pups than in WKY (94.5% Proteobacteria in WKY vs. 65.2% in SHR neonates). Even within the phylum Proteobacteria, the colonizing genera in WKY and SHR differed dramatically. Whereas WKY microbiota was predominantly comprised of Escherichia-Shigella, SHR microbiota was represented by other taxa of Enterobacteriaceae and Pasteurellaceae. In contrast, the representation of phylum Firmicutes in the neonatal SHR gut was greater than WKY. Cross-fostering newborn SHR pups by lactating WKY dams caused a dramatic shift in 1-week old cross-fostered SHR gut microbiota. The two major bacterial taxa of phylum Proteobacteria, Enterobacteriaceae and Pasteurellaceae as well as Lactobacillus intestinalis, Proteus, Romboustia and Rothia were depleted after cross-fostering and were replaced by the predominant genera of WKY (Escherichia-Shigella). A proinflammatory IL-17F producing CD161 + immune cell population in the spleen and aorta of cross-fostered SHR was also reduced (30.7% in self-fostered SHR vs. 12.6% in cross-fostered SHR at 30 weeks of age) as was the systolic blood pressure in adult cross-fostered SHR at 10 weeks of age. Thus, altered composition of gut microbiota of SHR toward WKY at early neonatal age had a long-lasting effect on immune system by reducing proinflammatory immune cells and lowering systolic blood pressure.

Early Postnatal Gut Microbiota Determines SHR Hypertension

Hypertension is regulated by immunological components. We have shown that spontaneously hypertensive rats (SHR) display a genetic abnormality in a large population of proinflammatory CD161+ immune cells. Although early postnatal gut microbiota is important for development of the immune system, this relationship has not been studied in hypertension. Cross‐fostering SHR pups by normotensive Wistar‐Kyoto (WKY) dams lowers the blood pressure in adulthood when cross‐fostering is initiated at a very young age. In this study, we tested whether early alteration in postnatal gut microbiota affect s the immune system and blood pressure of SHR. We first examined the microbial populations in the fecal samples of SHR and normotensive control WKY using 16s rDNA sequencing. We found that the newborn SHR (1‐week old) have abnormal gut microbiota that is qualitatively and quantitatively different from the newborns of normotensive WKY. The representation of the predominant bacterial phylum Proteobacteria was significantly less in 1‐week old SHR pups than in WKY (94% Proteobacteria in WKY vs. 65% in SHR neonates). Even within the phylum Proteobacteria, the colonizing genera in WKY and SHR differed dramatically. Whereas WKY microbiota was predominantly comprised of Escherichia‐Shigella (92.5%), SHR microbiota was represented by Klebsiella (34.7%) and Haemophilus (27.8%). In contrast, the representation of phylum Fermicutes in the neonatal SHR gut was greater than WKY (5% Fermicutes in WKY vs. 31% in SHR). We cross‐fostered newborn SHR pups by lactating WKY dams and measured the resulting changes in the gut microbiota, immune system and blood pressure. Cross‐fostering caused a dramatic shift in 1‐week old cross‐fostered SHR gut microbiota. The two major bacterial genera of phylum Proteobacteria, Klebsiella and Haemophilus, present in self‐fostered SHR pups, were depleted after cross‐fostering, and were replaced by the predominant genera of WKY (Escherichia‐Shigella). A proinflammatory CD161+ immune cell population in the spleen of cross‐fostered SHR was also reduced (30.7% in self‐fostered SHR vs. 12.6% in cross‐fostered SHR at 30 weeks of age) as was the systolic blood pressure in adult cross‐fostered SHR (SHR 204 mmHg vs. cross‐fostered SHR 177 mmHg, p= 0.02, n= 4 each group). Thus, cross‐fostering of SHR pups by WKY dams shifted the composition of their gut microbiota toward WKY within one week. Additionally, reduction in proinflammatory immune cells and lowering of systolic blood pressure were observed in cross‐fostered SHR. In summary, SHR have a congenital defect in their immune system that results in greater proinflammatory response associated with hypertension. Gut microbiota of the SHR is remarkably different from that of normotensive WKY, and likely contributes to SHR blood pressure by modulating early development of the immune system.Support or Funding InformationNational Institutes of Health Program Project Grant to FMA (HL 14388) VA Merit Review Award to MWC (1 I01BX001414), American Heart Association Innovative Research Grant to MVS (16IRG27260323).

Influence of Early Postnatal Gut Microbiota on Immune System in SHR Hypertension

Hypertension exhibits a prominent immunological component. We have recently shown that spontaneously hypertensive rats (SHR) have a genetic abnormality whereby they are born with a large population of proinflammatory CD161+ immune cells. Although early postnatal maternal environment is important for development of hypertension, its impact on the immune system is not known. Cross‐fostering SHR pups by normotensive Wistar‐Kyoto (WKY) dams lowers the blood pressure in adulthood only if the cross‐fostering is initiated at a very young age. In this study, we used SHR as a genetic model of hypertension to test whether early postnatal gut microbiota affect the immune system and blood pressure of SHR. Since cross‐fostering permanently changes the gut microbiota of the fostered offspring, we first examined the microbial populations in the fecal samples of SHR and normotensive control WKY using 16s rDNA sequencing. We found that the newborn SHR (1‐week old) have abnormal gut microbiota that is qualitatively and quantitatively different from the newborns of normotensive WKY. The representation of predominant bacterial phylum Proteobacteria was less in 1‐week old SHR pups (94% Proteobacteria in WKY vs. 65% in SHR neonates). Even within the phylum Proteobacteria, the colonizing genera in WKY and SHR differed dramatically. In contrast, the representation of phylum Fermicutes in the neonatal SHR gut was greater than WKY (5% Fermicutes in WKY vs. 31% in SHR). We also observed a dramatic shift in 1‐week old SHR gut microbiota when we cross‐fostered WKY and SHR pups beginning at 1‐day of age. Two major bacterial genera of phylum Proteobacteria present in self‐fostered SHR pups, but absent in WKY, were depleted after cross‐fostering, and were replaced by other bacteria predominant in WKY gut. Investigation of immune cells in the spleen of cross‐fostered SHR using cell surface markers and flow cytometry showed that there was a clear reduction in CD161+ cells (30.7% in self‐fostered SHR vs. 12.6% in cross‐fostered SHR at 30 weeks of age), a marker associated with inflammation. Thus, cross‐fostering of SHR pups by WKY dams shifted the composition of their gut microbiota toward WKY within one week. Additionally, preliminary results suggest lower systolic blood pressure (tail cuff pressure) in cross‐fostered SHR. In summary, SHR are born with a defect in their immune system that results in greater proinflammatory response associated with hypertension. Moreover, the gut microbiota of the SHR is remarkably different from that of normotensive WKY, and cross‐fostering of SHR by WKY dams favorably changes the gut microbiome and immune regulation.Support or Funding InformationNational Institutes of Health Program Project Grant to FMA (HL 14388) VA Merit Review Award to MWC (1 I01 BX001414), American Heart Association Innovative Research Grant to MVS (16IRG27260323).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Circadian alignment in a foster mother improves the offspring's pathological phenotype.

In mammals, the mother-offspring interaction is essential for health later in adulthood. The impact of altered timing and quality of maternal care on the offspring's circadian system was assessed using a cross-strain fostering approach. Better maternal care facilitated the development of amplitudes of Bmal1 clock gene expression in the central clock, as well as the clock-driven activity/rest rhythm, and also its entrainment to the external light/dark cycle. Worse maternal care impaired entrainment of the central clock parameters in the Wistar rat during the early developmental stages. Better maternal care remedied the dampened amplitudes of the colonic clock, as well as cardiovascular functions. The results provide compelling evidence that the circadian phenotype of a foster mother may affect the pathological symptoms of the offspring, even if they are genetically programmed. In mammals, the mother-offspring interaction is essential for health later in adulthood. Maternal care is determined by the circadian phenotype of the mother. The impact of altered timing and quality of maternal care on the circadian system was assessed using a cross-strain fostering approach, with 'abnormal' (i.e. circadian misaligned) care being represented by spontaneously hypertensive rats (SHR) and 'normal' care by Wistar rats. The SHR mothers worsened synchrony of the central clock in the suprachiasmatic nuclei with the light/dark cycle in Wistar rat pups, although this effect disappeared after weaning. The maternal care provided by Wistar rat mothers to SHR pups facilitated the development of amplitudes of the Bmal1 expression rhythm in the suprachiasmatic nuclei of the hypothalamus, as well as the clock-driven activity/rest rhythm and its entrainment to the external light/dark cycle. The peripheral clocks in the liver and colon responded robustly to cross-strain fostering; the circadian phenotype of the Wistar rat foster mother remedied the dampened amplitudes of the colonic clock in SHR pups and improved their cardiovascular functions. In general, the more intensive maternal care of the Wistar rat mothers improved most of the parameters of the abnormal SHR circadian phenotype in adulthood; conversely, the less frequent maternal care of the SHR mothers worsened these parameters in the Wistar rat during the early developmental stages. Altogether, our data provide compelling evidence that the circadian phenotype of a foster mother may positively and negatively affect the regulatory mechanisms of various physiological parameters, even if the pathological symptoms are genetically programmed.

Impact of Gestational Chronic Intermittent Hypoxia and Hypertension on the Serotonergic System and Autoresuscitation in the Developmental Rat

Sudden infant death syndrome (SIDS) is characterized by the sudden death of a seemingly healthy infant during a sleep period under the age of 12 months. Abnormalities in the medullary serotonin (5HT) system, e.g. decreased tissue levels of 5HT and 5HTT, and increased immature 5HT neurons, have been identified in approximately 70% of infants that died of SIDS. Failed autoresuscitation (inability to recover breathing and heart rate following hypoxic apnea) is considered a possible mechanism of SIDS deaths, and animal studies have shown that 5HT neurons are critical for neonatal mice and rats to survive repeated episodes of severe hypoxia/asphyxia. Gestational chronic intermittent hypoxia (CIH) and preeclampsia both are risk factors for SIDS. In this study we asked whether the stressors, e.g. gestational/prenatal chronic intermittent hypoxia (CIH) and/or hypertension, would increase stress hormone levels, impair the maturity and integrity of medullary 5HT neurons and the ability to autoresuscitate from repetitive asphyxia in developing rat pups. The pregnant dams of normotensive Sprague Dawley (SD) rats and spontaneously hypertensive rats (SHR) were exposed to CIH or room air (RA) from gestation E4‐21, and then the serum corticosterone level (ELISA), the number and integrity of the medullary serotonin neurons (immunostainings), and in vivo autoresuscitation were assessed in the offspring pups at Postnatal (P) days 5–15.We found 1) SHR‐CIH pups have significantly higher serum corticosterone levels than SHR‐RA and SD‐RA pups at P7 (11,485 vs. 8078 & 8970 pg/mL respectively, P<0.05) and P10 (11,708 vs. 9040 & 6,529 pg/mL respectively, P<0.05). At P15 SD‐CIH, SHR‐CIH and SHR‐RA pups all have significantly higher corticosterone levels than SD‐RA pups; 2) Relative to the SD‐RA pups, SD‐CIH pups have a significantly higher total number of 5HT neurons and primarily due to increased number of Ki67/5HT‐ir positive neurons in the medulla. When compared to SD rats, we noticed that SHR pups appear to have more Ki67/5HT‐ir neurons which contribute to an increase in total number of 5HT neurons in the medulla than SD‐CIH & SD‐RA (P<0.01); and 3) the offspring pups of SHRs have the highest mortality rate during repetitive exposure of anoxia at all ages tested. Our data suggest that both gestational CIH and uncontrolled hypertension may lead to an impaired 5HT system in the offspring pups. The uncontrolled high blood pressure during pregnancy may cause placental insufficiency and contribute to failed autoresuscitation in response to repetitive anoxia in early postnatal life.Support or Funding InformationDartmouth UGAR, NIH HD036379, NIH HL28066

Effect of melatonin supplementation and cross-fostering on renal glutathione system and development of hypertension in spontaneously hypertensive rats

Antenatal and postnatal environments are hypothesised to influence the development of hypertension. This study investigates the synergistic effect of cross-fostering and melatonin supplementation on the development of hypertension and renal glutathione system in spontaneously hypertensive rats (SHR). In one experiment, 1-day-old male SHR pups were fostered to either SHR (shr-SHR) or Wistar-Kyoto rats, (shr-WKY). In a concurrent experiment, SHR dams were given melatonin in drinking water (10 mg/kg body weight) from day 1 of pregnancy. Immediately following delivery, 1-day-old male pups were fostered either to SHR (Mel-shr-SHR) or WKY (Mel-shr-WKY) dams receiving melatonin supplementation until weaning on day 21. Upon weaning, melatonin supplementation was continued to these pups until the age of 16 weeks. Systolic blood pressures (SBP) were recorded at the age of 4, 6, 8, 12 and 16 weeks. Renal antioxidant activities were measured. Mean SBP of shr-WKY, Mel-shr-SHR and Mel-shr-WKY was significantly lower than that in shr-SHR until the age of 8 weeks. At 12 and 16 weeks of age, mean SBP of Mel-shr-WKY was lower than those in non-treated shr-SHR and shr-WKY pups but was not significantly different from that in Mel-shr-SHR. Renal glutathione peroxidase (GPx) and glutathione S-transferase (GST) activities were significantly higher in Mel-shr-SHR and Mel-shr-WKY at 16 weeks of age. It appears that combination of cross-fostering and melatonin supplementation exerts no synergistic effect on delaying the rise in blood pressure in SHR. The elevated GPx and GST activities are likely to be due to the effect of melatonin supplementation.

Effects of antenatal, postpartum and post-weaning melatonin supplementation on blood pressure and renal antioxidant enzyme activities in spontaneously hypertensive rats

Although melatonin lowers blood pressure in spontaneously hypertensive rats (SHR), its effect following antenatal and postpartum supplementation on the subsequent development of hypertension in SHR pups remains unknown. To investigate this, SHR dams were given melatonin in drinking water (10mg/kg body weight/day) from day1 of pregnancy until day21 postpartum. After weaning, a group of male pups continued to receive melatonin till the age of 16weeks (Mel-SHR), while no further melatonin was given to another group of male pups (Maternal-Mel-SHR). Controls received plain drinking water. Systolic blood pressure (SBP) was measured at 4, 6, 8, 12 and 16weeks of age, after which the kidneys were collected for analysis of antioxidant enzyme profiles. SBP was significantly lower till the age of 8weeks in Maternal-Mel-SHR and Mel-SHR than that in the controls, after which no significant difference was evident in SBP between the controls and Maternal-Mel-SHR. SBP in Mel-SHR was lower than that in controls and Maternal-Mel-SHR at 12 and 16weeks of age. Renal glutathione peroxidase (GPx) and glutathione s-transferase (GST) activities, levels of total glutathione and relative GPx-1 protein were significantly higher in Mel-SHR. GPx protein was however significantly higher in Mel-SHR. No significant differences were evident between the three groups in the activities of superoxide dismutase, catalase and glutathione reductase. In conclusion, it appears that while antenatal and postpartum melatonin supplementation decreases the rate of rise in blood pressure in SHR offspring, it however does not alter the tendency of offspring of SHR to develop hypertension.

Atenolol Reduces Salivary Activity in Pups of Spontaneously Hypertensive and Normotensive Rats Treated during Pregnancy and Lactation

The salivary activity in pups of spontaneously hypertensive rats (SHR) and Wistar (W) rats treated with atenolol during pregnancy, and lactation was evaluated. Atenolol's anti-hypertensive effect on the SHR rats was noticed from the beginning of treatment. Atenolol-treated SHR and Wistar rat pups showed a decrease in salivary gland weight, salivary flow, and protein concentration, with no alteration in salivary amylase activity. Atenolol's effect on salivary glands can interfere with oral health maintenance.

The Pregnant Spontaneously Hypertensive Rat as a Model of Asymmetric Intrauterine Growth Retardation and Neurodevelopmental Delay

Introduction. Hypertension in pregnancy and vascular placental insufficiency are considered common pathogenic factors in human intrauterine growth retardation (IUGR). IUGR neonates experience higher mortality, and the surviving infants have a higher incidence of neurological and intellectual impairment. Methods. To mimic this condition, we used pregnant spontaneously hypertensive rats (SHR) and performed biometric measurements on Embryonic Day 20, postnatal developmental reflexes, and locomotor activity evaluations. Results. SHR fetuses had significant decreased body weight compared to the Wistar-Kyoto control fetuses (1.51 ± 0.02 g vs. 2.05 ± 0.01 g, respectively; p < 0.0001), and were relatively microcephalic (2.86 ± 0.04 cm vs. 3.3 ± 0.03 cm, respectively; p < 0.0001). Their cephalization index (head circumference/body weight) was increased (1.88 ± 0.03 vs. 1.62 ± 0.02, respectively; p < 0.0001), indicating a “brain-sparing” process. The disproportional ratio indicated that the IUGR type in this model is asymmetric. The SHR pups exhibited a significant (p < 0.04) neurodevelopmental delay in the acquisition of neonatal reflexes (righting, negative geotaxis, placing), but they spontaneously caught up with the control pups after approximately 10 days. On Day 30, the SHR pups exhibited significantly increased walking speed and distance and spent less time in quadrant than the controls (p < 0.002). Conclusion. We speculate that the model of pregnant SHR closely simulate human IUGR caused by hypertension in pregnancy and should enable investigation of mechanisms of hypertension-mediated placenta-vascular injury as well as provide a system for preclinical evaluations of future preventive neuroprotective treatments.

Renal renin-angiotensin system activity in naturally reared and cross-fostered spontaneously hypertensive rats

BackgroundYoung (4 week) spontaneously hypertensive rats (SHR) exhibit greater renal responses to angiotensin II (Ang II) than normotensive Wistar Kyoto (WKY) rats. SHR pups cross-fostering to a WKY dam at birth (SHRX) are less sensitive to Ang II and have lower adult blood pressure. The aim of this study was to compare renal renin-angiotensin system activity in young naturally reared and cross-fostered SHR pups. MethodsSHR and WKY rats were reared either by their natural mothers or by a foster mother of the opposite strain. At 5, 10, and 15 days of age, renal tissue renin activity and Ang II concentration were measured by radioimmunoassay. Renin-secreting cells were identified by in situ hybridization and AT1 receptor expression was compared using Western blots. Ang II-mediated cAMP generation was measured in isolated proximal tubules. ResultsTissue renin activity and numbers of renin-secreting cells did not differ, but Ang II was higher in SHRX. The AT1 receptor expression was significantly lower in SHRX compared with SHR. Basal and Ang II-stimulated cAMP was lower in SHR tubules compared with WKY and SHRX tubules. ConclusionsCross-fostering reversed the increased renal sensitivity of the SHR to Ang II. These data suggest that renal AT1 receptor expression can be manipulated during the postnatal period and that this may affect adult blood pressure.

Composition en acides gras des hémisphères cérébraux de rats spontanément hypertendus allaités par des femelles Wistar

Total lipid fatty acid composition was investigated in brain hemispheres of male Spontaneously Hypertensive Rats (SHR), compared with normotensive Wistar Kyoto rats (WKY) used as controls. Both strains were suckled by adoptive Wistar mothers, and then fed a standard diet after weaning. No difference was observed between the two hemispheres of WKY killed either at 10 or 30 days. In SHR killed at 10 days, the two hemispheres showed differences, SHR left hemispheres exhibiting greater fatty acid composition changes than those of WKY, phenomenon that toned down at 30 days. Hence, SHR pups showed a different total lipid fatty acid composition of their brain hemispheres when compared with their WKY controls, though the two strains received the same diet. Genetically programmed hypertension might be, directly or not, involved in these changes. To cite this article: J.-L. Savelli et al., C. R. Biologies 326 (2003).

Effect of cross-fostering on neonatal sodium balance and adult blood pressure in the spontaneously hypertensive rat.

1. The aim of the present study was to compare electrolyte handling in naturally reared neonatal spontaneously hypertensive rats (SHR) with those reared by a Wistar-Kyoto (WKY) rat foster mother (denoted SHRX), as cross-fostering SHR pups to a WKY rat dam lowers adult blood pressure in the SHR. 2. The electrolyte content of WKY rat and SHR dams' milk was determined and electrolyte intake and urinary excretion rates were calculated in both naturally reared and cross-fostered WKY rat and SHR pups. 3. The milk sodium concentration fell in both strains (WKY rat: 31.8 +/- 2.0 to 15.2 +/- 1.2 mmol/L; SHR 31.9 +/- 2.5 to 18.2 +/- 1.6 mmol/L; P < 0.001), as did potassium (P < 0.001), over lactation, but there were no differences between strains. Calcium and magnesium concentrations increased (P < 0.001), although SHR dam's milk contained less calcium (P < 0.001) than that of WKY rat dams during the third week of lactation. 4. Spontaneously hypertensive rat pups ingested less milk (P < 0.05) than WKY rat pups; therefore, their cumulative sodium intake over postnatal days 4-15 was significantly lower than that of WKY rat pups (WKY rat vs SHR: 84.4 +/- 3.6 vs 59.7 +/- 2.6 mumol/g bodyweight, respectively; P < 0.05) and fostered SHRX pups (77.7 +/- 7.0 mumol/g bodyweight; P < 0.05). Potassium and magnesium intakes were comparable between SHR, WKY rat and SHRX pups, but SHR pups ingested significantly less calcium than either WKY rat pups (136.1 +/- 6.4 vs 200.1 +/- 9.5 mumol/g bodyweight, respectively; P < 0.05) or SHRX pups (200.0 +/- 18.0 mumol/g bodyweight; P < 0.05). 5. These data show that the neonatal SHR experiences a period of sodium deficiency during the developmental stage when cross-fostering is effective in lowering blood pressure. This is consistent with the reported up-regulation of the renin-angiotensin system observed in SHR at this time and may have a long-term influence on blood pressure.

Early postnatal changes in sarcoplasmic reticulum calcium transport function in spontaneously hypertensive rats.

This comparative study investigates the relationship between sarcoplasmic reticulum (SR) calcium(Ca2+)-ATPase transport activity and phospholamban (PLB) phosphorylation in whole cardiac homogenates of spontaneously hypertensive rats (SHR) and their parent, normotensive Wistar Kyoto (WKY) strain during early postnatal development at days 1, 3, 6, 12 and at day 40 to ascertain any difference in SR Ca2+ handling before the onset of hypertension. At day 1, the rate of homogenate oxalate-supported Ca2+ uptake was significantly higher in SHR than in WKY (0.25 +/- 0.02 vs 0.12 +/- 0.01 nmoles Ca2+/mg wet ventricular weight/min, respectively; p < 0.001). This interstrain difference disappeared with further developmental increase in SR Ca2+ transport. Western Blot analysis and a semiquantitative ELISA did not reveal any difference in the amount of immunoreactive PLB (per mg of total tissue protein) between strains at any of the ages studied. In addition, levels of phosphorylated PLB formed in vitro in the presence of radiolabelled ATP and catalytic (C) subunit of protein kinase A did not differ between SHR and WKY at days 1, 3, 6 and 12. At day 40, C subunit-catalyzed formation of 32P-PLB was reduced by 66% (p < 0.001) in SHR when compared to age-matched WKY. In the early postnatal period between day 1 and 12 SR Ca(2+)-transport values were linearly related to the respective 32P-PLB levels of both SHR and WKY rats. The results indicate that cardiac SR of SHR can sequester Ca2+ at a much higher rate immediately after birth compared to WKY rats. The disappearance of this interstrain difference with further development suggests that some endogenous neuroendocrine or nutritional factor(s) from the hypertensive mother may exert an influence upon the developing heart in utero resulting in a transiently advanced maturation of the SR Ca2+ transport function in SHR pups at the time of birth.

Enduring effects of infant feeding experiences on adult blood pressure.

Vulnerability to psychosomatic diseases is influenced by events early in life. The objective of this article is to discuss animal research that demonstrates relationships between feeding experiences and growth in infancy and risk of hypertension in adulthood. Subjects were spontaneously hypertensive rats (SHR) and their normotensive Wistar Kyoto progenitors. Initial experiments involved observations of the behaviors of rat mothers and their infants and follow-up measurements of blood pressures. Further studies focused on measurements of infant blood pressure during feeding, and recent investigations manipulated weight gain and sex hormones early in life. Infant rats whose mothers were seen nursing more often had increased blood pressure as adults. Each time rat mothers delivered milk to their young, the nursing pups' blood pressures rose dramatically. These feeding-induced increases in blood pressure have been observed in the young of many species including humans. They are mediated by autonomic nervous system activity and are larger in SHR pups. Finally, animals that gain weight rapidly as infants as a consequence of being reared in small litters had higher adult blood pressure; but, this effect is seen only in intact males. Adult physiologic traits can be influenced by the joint actions of genetic predisposition and essential psychosocial interactions during early development. Animal models can stimulate new ideas, provide important confirmations and elaborations of hypotheses from human investigations, and afford experimental approaches for identifying mechanisms underlying the transduction of behavioral experience to disease susceptibility.

Pharmacological blockade of blood pressure and heart rate increases following milk ingestion in 15-day-old SHR and WKY rat pups

The effects of hexamethonium, a ganglionic blocker, on blood pressure (BP) and heart rate (HR) responses to milk ingestion were assessed in awake, 15-day-old spontaneously hypertensive rats (SHR) and their normotensive progenitor strain, Wistar-Kyoto rats (WKY) using two methods of milk delivery. SHRs had larger increases in BP compared to WKYs, but WKYs exhibited larger increases in HR following milk ingestion from an anesthetized dam. BP responses to milk ingestion from a tongue cannula were also larger in SHRs. Administration of hexamethonium prior to milk delivery resulted in a drop in BP following milk ingestion in both milk delivery situations for each strain. The results suggest that SHRs exhibit exaggerated sympathetic activation to milk ingestion compared to WKYs, and that in both strains, cardiovascular responses to feeding are modulated by the presence of the dam.

The Influence of Prenatal Salt on the Development of Hypertension by Spontaneously Hypertensive Rats (SHR)

SummarySpontaneously hypertensive rat (SHR) pups whose mothers receive a high salt diet during pregnancy and who continue on the high salt diet in postnatal life develop exceedingly high blood pressures (230 mm Hg before 4 months of age). This does not occur in SHR on high salt only prenatally or only postnatally nor does it occur in Wistar Kyoto (WKY) or Sprague Dawley (CD) rats. Among SHR pups on the high salt regimen both pre- and postnatally there is a greatly accelerated incidence of stroke as well as a markedly shortened life-span (36% mortality before 4 months of age). Maternal effects of the high salt diet include reduced gestational weight gain, and reduced successful pregnancies in SHR and WKY. However, in successful pregnancies maternal blood pressures in all three strains were not significantly altered by the high salt diet. The high salt diet did not affect the life span of the mothers, and the SHR mothers of pups on high salt both pre- and postnatally outlived their offspring.