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D C Hatton

Publications and source records attributed to D C Hatton.

At least 55 records · Page 3Linked to original sources
PubMed1991

The interactive effects of dietary sodium chloride and calcium on cardiovascular stress responses.

Blood pressure increases associated with salt loading in the spontaneously hypertensive rat (SHR) are attenuated with increased dietary calcium. To assess the cardiovascular effects of these nutrients during stress, blood pressure and sympathoadrenal responses to stress were compared in salt-sensitive SHRs fed diets containing normal (0.73%) or high (8.0%) NaCl combined with either low (0.2%) or high (2.0%) calcium. NaCl-loaded rats showed increased blood pressure and exaggerated plasma epinephrine changes during restraint stress. Elevated blood pressure responses to exogenous NE were also observed with high salt intake. Supplementary calcium reduced blood pressure and attenuated the hypertensive effect of NaCl during restraint stress. Animals fed the high calcium diets had lower plasma epinephrine levels while vascular reactivity was not affected. The results indicate that increased sympathoadrenal activity and vascular reactivity contribute to elevated blood pressure and exaggerated pressor responses produced by NaCl loading in the salt-sensitive SHR. However, the hypotensive effects of dietary calcium appear to be related to sympathoadrenal activity but not vascular reactivity.

Analysis of Variance↗
PubMed1991

Role of anteroventral third ventricle and vasopressin in renal response to stress in borderline hypertensive rats.

The borderline hypertensive rat is the first filial offspring of the spontaneously hypertensive rat and the Wistar-Kyoto rat. In response to acute environmental stress (air jet), the borderline hypertensive rat exhibits a diuretic response, whereas the parental strains exhibit an antidiuretic response (spontaneously hypertensive rat) or no change in urine flow rate (Wistar-Kyoto rat). This study sought to investigate the role of the periventricular tissue surrounding the anteroventral third ventricle and vasopressin release in the diuretic response of the borderline hypertensive rat to acute environmental stress. Sixteen-week-old borderline hypertensive rats who had consumed a 1% NaCl diet for 10-12 weeks were given either electrolytic lesions of the anteroventral portion of the third ventricle or sham lesions. When exposed to acute environmental stress 4 weeks later, the increase in volume of dilute urine seen in the sham-lesion rats was not observed in the lesion rats. Plasma vasopressin concentration was decreased by acute environmental stress in the sham-lesion rats (15.2 +/- 4.0 to 10.9 +/- 1.7 pg/ml, p less than 0.05) but was unchanged in the lesion rats (12.3 +/- 2.0 to 13.4 +/- 4.0 pg/ml). In a separate group of intact borderline hypertensive rats, a constant intravenous infusion of vasopressin prevented the diuretic response to acute environmental stress. The results suggest that acute environmental stress produces a diuresis in the borderline hypertensive rats via a decrease in plasma vasopressin concentration that is dependent on the integrity of the periventricular tissue of the anteroventral portion of the third ventricle.

Animals↗
PubMed1991

Effects of dietary sodium and calcium on blood pressure reactivity in the SHR and WKY.

Salt-sensitive spontaneously hypertensive rats (SHR) and their normotensive control strain, Wistar-Kyoto rats (WKY) were fed four diets varying in sodium chloride and calcium content in order to assess the effects of diet on learned blood pressure responses. The animals were exposed to a classical conditioning paradigm in which one tone was always followed by a brief electric shock and a second tone was never followed by shock. Sodium chloride loading raised baseline blood pressure in both strains, while supplemental calcium attenuated blood pressure. Sodium chloride potentiated blood pressure orienting responses to initial presentations of the tones among calcium deficient, but not calcium replete SHR. Increased sodium chloride intake also potentiated the learned pressor responses to the tone paired with shock in the SHR, but not the WKY. Calcium intake had no apparent effect on the learned blood pressure responses to the two tones.

Animals↗
PubMed1989

Psychophysiological factors in ventricular arrhythmias and sudden cardiac death.

Plasma catecholamine levels were measured preceding programmed electrophysiological studies of patients who had survived a ventricular tachyarrhythmia episode. Psychological assessments of desire for control, locus of control and behavior pattern were obtained. Psychophysiological variables were analysed with respect to the severity of arrhythmias induced by the electrophysiological procedure. Analysis of data from 17 subjects showed desire for control was significantly higher in those with induced sustained arrhythmias than in those in which nonsustained arrhythmias were induced. No relationship was found between behavior pattern and arrhythmia severity or plasma catecholamine levels. There was a significant interaction between desire for control and behavior pattern with respect to epinephrine level. The findings indicate that psychological factors such as desire for control may be associated with potentially lethal arrhythmias and implicated in sudden cardiac death.

Adult↗
PubMed1989

Dietary calcium alters blood pressure in neonatal spontaneously hypertensive rats.

Dietary alterations in young genetically hypertensive rats have been shown to have a substantial impact on subsequent blood pressure (BP) development. In the present study, spontaneously hypertensive rat (SHR) pups fostered at birth to high calcium (2%) SHR dams developed significantly lower mean arterial pressures by 28 days of age than pups fostered to low calcium (0.1%) dams (93.7 v 107.7 mm Hg, P less than .01). To determine whether BP differences were due to milk ingestion or to late lactational solid diet consumption, a second experiment was performed. Pups were fostered at birth to medium calcium (1.0%) dams and weaned at 21 days to one of three calcium diets. Blood pressures were determined at 28 days after birth. Pups weaned to the high diet at 21 days had lower pressures at 28 days than pups weaned to the low diet (94.2 v 108.3, P less than .01), suggesting that the pressure variations in the first experiment were due primarily to solid food consumption by the pups late in the suckling period. This rapid BP alteration suggests that neonatal SHR have an enhanced susceptibility to the pressure effects of dietary calcium.

Aging↗
PubMed1989

Dietary calcium alters blood pressure reactivity in spontaneously hypertensive rats.

Plasma catecholamines and blood pressure reactivity were investigated in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats maintained on three levels of dietary calcium: low (0.1%), intermediate (1.0%), or high (2.0%). In the SHR, restricted dietary calcium resulted in elevations of mean arterial pressure that were most pronounced during handling and restraint stress (p less than 0.05). There was no difference between SHR on intermediate and high calcium diets and no dietary effects in the WKY rats. Resting and stressed levels of circulating catecholamines did not differ across diet conditions in either strain. The SHR on low calcium diets had significantly larger pressor responses to infused norepinephrine (p less than 0.05). There were no differences between the rats on intermediate and high calcium diets. The results indicate that differences observed in blood pressure reactivity across diets in this study may have been a consequence of altered postsynaptic sensitivity rather than an increase in norepinephrine release.

Animals↗
PubMed1987

Genetic variability in response to dietary calcium.

Supplemental dietary calcium has been shown to reduce blood pressure in spontaneously hypertensive rats while restricted calcium diets cause an elevation in blood pressure. This latter nutrient effect has been enhanced by modest sodium restriction and is associated with a reduction in serum ionized calcium concentration. To determine whether alterations of dietary calcium and sodium have a similar influence on blood pressure in genetically normotensive rats, Fisher 344, Wistar Furth, and ACI rats were fed either a low (0.1%) calcium, low (0.25%) sodium diet or normal (1.0%) calcium, normal sodium (0.45%) diet from 4 weeks of age through 29 weeks of age. Indirect measurements of systolic blood pressure showed that only the Fisher 344 rats consistently responded to the low calcium/low sodium diets with an elevation of blood pressure. There was considerable variation in serum electrolytes across strains in the normal diets but all three strains experienced a reduction in ionized calcium and an elevation in phosphorus and magnesium on the restricted diets. In the Fisher 344 rats there were significant (p less than .05) inverse correlations among systolic blood pressure and serum ionized and total calcium concentrations and positive correlations among systolic blood pressure, phosphorus, and magnesium. There was no significant correlation between serum electrolytes and blood pressure in the other two strains. The data indicate that there is genetic variability in the blood pressure response to alterations in dietary calcium and sodium. The pattern of change in serum electrolytes across strains suggests that diet-induced alterations of serum electrolytes, specifically calcium, are not necessarily predictive of a pressor response. It would appear that some other calcium-sensitive physiological process involved in blood pressure regulation must respond differentially to calcium availability across strains.

Animals↗
PubMed1987

Psychosocial stress, dietary calcium and hypertension in the spontaneously hypertensive rat.

The interactive effects of psychosocial stress and diet on the development of hypertension were investigated in spontaneously hypertensive rats. Psychosocial stress, produced through manipulation of group housing conditions, was evaluated at three levels of dietary calcium and sodium: Low (0.1% Ca2+, 0.25% Na+), Intermediate (1.0% Ca2+, 0.45% Na+), and High (2.0% Ca2+, 1.0% Na+). After 13 weeks of exposure, stressed animals had higher blood pressure and lower serum ionized calcium than nonstressed animals across all diets. Likewise, animals on the low diet had higher blood pressures and lower ionized calcium values than animals on normal or high diets regardless of stress condition. The combination of stress and low diet produced the highest blood pressure and lowest serum ionized calcium values. The results suggest that stress both independently and in combination with dietary Ca2+ altered calcium metabolism. The interaction between psychosocial stress and dietary factors appears to contribute to reductions in serum ionized calcium and elevations in blood pressure in this experimental model of genetic hypertension.

Animals↗
PubMed1987

Stress-induced blood pressure responses in SHR: effect of dietary calcium.

To assess the influence of dietary calcium on stress-induced blood pressure responses, spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were placed on low Ca2+ (0.1%) and Na+ (0.25%), intermediate Ca2+ (1.0%) and Na+ (0.45%), or high Ca2+ (2.0%) and Na+ (1.0%) diets for 13 wk prior to measuring blood pressure (BP) responses in an aversive classical conditioning paradigm. Forty-eight hours prior to testing, catheters were placed in a femoral artery under halothane anesthesia for recording direct pressure. On recovery the rats were classically conditioned to a 10-s tone followed by a brief electric shock using a discrimination paradigm. After 24 reinforced trials, SHRs on a low diet had significantly larger pressor responses to the conditioned tones than rats in the high diet condition. SHRs on the intermediate diet exhibited pressor responses midway between the low and high diet groups. In the WKY strain there was no significant dietary effect on conditioned BP response. In both strains the low diets resulted in significantly elevated base-line blood pressure levels. The data confirm earlier reports of elevated BP in SHRs and WKYs following dietary calcium restriction and provide suggestive evidence that the elevation in base-line BP may be related to diet-induced changes in BP reactivity in the SHR.

Animals↗
PubMed1986

Blood pressure development and serum calcium in suckling spontaneously hypertensive rat pups: effects of maternal dietary calcium.

Since perinatal factors and dietary calcium intake have been implicated in the early pathogenesis of hypertension in the spontaneously hypertensive rat (SHR), the effect of maternal dietary calcium intake on blood pressure development in the 3-4-week-old suckling SHR was assessed. Twenty-four 6-week-old female SHR were randomized to either a calcium- (0.1%) and sodium- (0.25%) restricted or calcium- (2.0%) and sodium- (1.0%) supplemented diet. After 19 weeks on the diet they were bred. Immediately following birth, half of the pups were cross-fostered to a dam on the alternative diet and half were fostered to a dam on the same diet as that to which they were exposed in utero. Between the 25th and 28th post-natal day each pup had an intra-arterial catheter placed in a femoral artery. Mean arterial pressure (MAP), serum ionized calcium and total calcium were measured. Pups fostered to dams on restricted-Ca2+ diets had higher MAP (P less than 0.01) and lower serum ionized (P less than 0.01) and total (P less than 0.01) calcium levels. There was a significant inverse correlation between serum ionized Ca2+ and MAP in the pups (r = -0.61, P greater than 0.001). We conclude that maternal dietary calcium intake may be an important perinatal factor in the blood pressure development of the suckling SHR.

Animals↗
PubMed1984

Baroreceptor involvement in classically conditioned heart rate responses of restrained rats.

A group (N = 8) of restrained, baroreceptor denervated rats and a sham-operated-control group (n = 8) received discriminated classical conditioning consisting of 30 reinforced trials in which a CS+ was paired with an electric shock US and 30 non-reinforced trials in which a different CS (CS-) was presented alone. The control group displayed a decelerative heart rate CR and a biphasic pressor-depressor blood pressure CR. The denervated group failed to show a heart rate CR but did show a pressor-only blood pressure CR. The URs of the denervated group consisted of a major depressor change in blood pressure and a slight tachycardia whereas the URs of the control group consisted of a slight pressor response and tachycardia. The results indicated that centrally initiated activity in the efferent vagal pathways mediating the decelerative HR CR in rats may be blocked by the absence of normal afferent baroreceptor neural discharge. An integrating role of baroreceptor input was also suggested for the URs.

Animals↗
PubMed1984

Effects of drug-induced changes in resting blood pressure on classically conditioned heart rate and blood pressure in restrained rats.

Subsequent to receiving aversive classical conditioning, which led to a decelerative heart rate (HR) conditioned response (CR) and a pressor-depressor blood pressure (BP) CR, three separate groups of restrained rats received intravenous infusion of sodium nitroprusside (40 micrograms/mg/min) to lower baseline BP, phenylephrine (17 micrograms/mg/min) to raise baseline BP, or an equivalent volume of saline. Conditioning test trials during infusion revealed that hypotension produced by sodium nitroprusside eliminated the HR CR and transformed the BP CR into a pressor-only reaction. Hypertension produced by phenylephrine facilitated the HR CR and changed the BP CR to a pressor-only response on selected trials in which baseline BP increases and baseline HR decreases were within restricted limits. Following drug withdrawal, the HR CRs of both drug groups and the BP CR of the phenylephrine group were attenuated. The unconditioned responses to the shock unconditioned stimulus under phenylephrine were exaggerated and consisted of tachycardias and depressor BP changes, whereas under sodium nitroprusside reduced tachycardias and depressor activity occurred. The results suggested that the loss of the vagally mediated HR CR under sodium nitroprusside was due to baroreceptor-controlled inhibition of vagal discharge and that the enhancement of the HR CR under phenylephrine was due to baroreceptor-influenced facilitation of vagal discharge.

Animals↗
PubMed1981

Autonomic control of heart rate and blood pressure in spontaneously hypertensive rats during aversive classical conditioning.

An examination was made of the heart rate (HR) and blood pressure (BP) responses of 7-9-wk-old spontaneously hypertensive rats (SHR) and genetical control Wistar/Kyoto (WKY) rats during aversive classical conditioning. Subsequent to the development of conditioned responding (CRs), assessments were made of the effects of selective autonomic blockade by methyl atropine (10 mg/kg), phentolamine (2 mg/kg), and propranolol (2 mg/kg). The CR complex in the two strains consisted of pressor BP CRs in conjunction with vagally mediated decelerative HR CRs in the SHR strain and sympathetically mediated accelerative HR CRs in the WKY strain. The decelerative SHR HR CR did not appear to be secondary to baroreceptor reflex activity, although such activity did appear to be involved in the pressor BP and decelerative HR orienting response (OR) and unconditioned response (UR) complex of the SHRs on the initial application of the CS and the US, respectively. Augmented pressor BP ORs, CRs, and URs in the SHRs relative to the WKYs and differential drug effects on BP and HR baselines of the two strains suggested the presence of enhanced sympathetic activity in the SHRs that was not reflected in the SHR decelerative HR CR. Phentolamine unmasked evidence of reflex beta 2-vasodilation deficiency in the SHRs that could have contributed to the enhancement of their BP OR and CR.

Animals↗