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R J Contreras

Publications and source records attributed to R J Contreras.

At least 37 records · Page 2Linked to original sources
PubMed1989

High fat/sucrose feeding attenuates the hypertension of spontaneously hypertensive rats.

To assess the caloric and cardiovascular effects of dietary obesity on an important animal model of hypertension research, 60-day-old male spontaneously hypertensive (SHR) rats were fed either Agway pelleted chow (Pellet), a diet enriched in fat and sucrose (HF/M), or alternated (Cycled) between 2-week periods of HF/M diet and Agway pelleted chow. After 14 weeks, HF/M feeding elevated the body weight of SHR rats by 15% over the body weight of pellet-fed control rats. This relative obesity was accompanied by heavier white (retroperitoneal) and brown (interscapular) fat pads, heavier heart weights, and tachycardia. Paradoxically, the systolic blood pressure levels of SHR rats fed the HF/M diet were reduced. Ruled out as an explanation for the blood pressure reduction was the relative polyunsaturated to saturated fat (P/S) rati of the diet. The hypertension of SHR rats may be due in part to the effects of an underlying metabolic problem that is counteracted by the effects of HF/M feeding; HF/M feeding not only elevated body weight but also reversed the hypoinsulinemia found in pellet-fed SHR rats. The Cycled group evidenced large up-and-down swings in caloric intake that coincided with HF/M and Pellet feeding; this produced modest staircase-like changes in body weight gain. Similar to the HF/M group, the systolic blood pressure level of the Cycled group was also reduced in comparison to the blood pressure level of the Pellet group. However, the Cycled group was found to be more responsive to the pressor effects of intravenous phenylephrine, an alpha-adrenergic agonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Differences in perinatal NaCl exposure alters blood pressure levels of adult rats.

To determine the effect of differences in NaCl intake early in development on adult blood pressure levels, adult Sprague-Dawley female rats were maintained on diets containing either 0.12, 1.0, or 3.0% dietary NaCl throughout pregnancy and lactation. The offspring were continued on these same diets to 30 days postpartum. Thereafter, all offspring were maintained on the same stock diet containing 1% NaCl. Beginning at 60 days, systolic blood pressure and heart rate were measured weekly for the next 6 wk by tail-cuff plethysmography in lightly etherized rats. Mean arterial pressure (MAP) and heart responses to the subcutaneous sequential administration of 100 micrograms/kg angiotensin II and 15 micrograms/kg isoproterenol were then obtained from the catheterized femoral or carotid artery in awake unrestrained rats. Rats raised on 3% NaCl diet had significantly higher base-line MAPS (127.1 mmHg) than rats raised on the 1% (117.4 mmHg) or 0.12% (115.8 mmHg) salt diets. The highest salt group was also significantly more responsive to the pressor effects of angiotensin II (+46.4 mmHg) and the depressor effects of isoproterenol (-41.4 mmHg) than the mid- (+35.6 and -32.2 mmHg) and low- (+26.9 and -32.5 mmHg) salt groups. Thus there is a sensitive period early in ontogenesis of the normotensive Sprague-Dawley rat during which blood pressure and blood pressure responsiveness to angiotensin II and isoproterenol may be influenced permanently by dietary NaCl.

Angiotensin II↗
PubMed1989

Dietary obesity and weight cycling: effects on blood pressure and heart rate in rats.

The overconsumption of rich and palatable foods and "yo-yo" dieting are feeding patterns involved in obesity and possibly hypertension in humans. We therefore examined the effects of diet-induced obesity and weight cycling on the blood pressure and heart rate levels of 60-day-old male normotensive Sprague-Dawley (S-D) and spontaneously hypertensive (SHR) rats. Six months on a high-fat and high-sucrose diet (HF/M) produced a greater obesity in S-D rats than in SHR rats. The caloric intakes of S-D rats fed the HF/M diet were greater than the caloric intakes of pellet-fed controls, whereas those of SHR rats were similar. The obesity of both strains was associated with hyperinsulinemia, heavier white (retroperitoneal) and brown (interscapular) fat pads, heavier heart weights, and tachycardia. Despite these changes, diet-induced obesity failed to increase systolic blood pressure obtained under light ether anesthesia or mean arterial pressure in the conscious state. Paradoxically, the blood pressures of SHR rats fed HF/M diet were reduced perhaps as a result of the high polyunsaturated fat component of the diet. A second S-D dietary obese group was alternated between 2-wk periods of unrestricted HF/M diet and 50% restricted pellet chow. Although their body weights were similar to pellet-fed controls, three cycles of weight loss and weight regain resulted in the consumption of increased dietary fat, increased food efficiency, heavier fat pads, and hyperinsulinemia. Heart rate and to some extent blood pressure fluctuated with diet, being elevated during HF/M feeding and reduced during restricted pellet feeding. Although weight cycling intensified the physiological responses to food ingestion, we found that weight cycling in dietary obese S-D rats did not elevate blood pressure levels.

Animals↗
PubMed1988

Weight cycling in female rats increases dietary fat selection and adiposity.

The effect of repeated food restriction-refeeding (weight cycling) on macronutrient selection and adiposity was investigated in female Sprague-Dawley rats. Rats were maintained on ad lib macronutrient self-selection and were put on one of two types of restriction. One group was reduced to 75% of their body weight on restricted amounts of chow and a second group was given ad lib chow during the concurrent period and were voluntarily hypophagic. During refeeding on macronutrient self-selection, animals previously restricted selected a higher percentage of dietary fat, had larger adipose depots and plasma insulin values, and had lower heart weights both expressed in grams and as a percentage of body weight than non-restricted groups. This suggests that both severe and moderate periods of restriction may have negative health consequences.

Animals↗
PubMed1987

Maternal dietary NaCl intake influences weanling rats' salt preferences without affecting taste nerve responsiveness.

The present study examined the relationship between maternal dietary NaCl intake during the period from conception through weaning and weanling rats' elective consumption of salt; the study asked whether or not changes in offsprings' salt intake was mediated by altered taste responsiveness. The subjects were the 21-day-old offspring of 24 adult female rats fed diets containing .08% (low), 1% (mid), or 4% (high) NaCl from conception through weaning. Maternal dietary salt levels influenced offsprings' salt intake. In long-term food choice tests, the mid and high salt rats ate more salted food and had higher salt preferences than the low salt animals; in long-term solution choice tests, the mid and high salt rats drank more saline and less water and had higher saline preferences than the low salt rats. Nevertheless, the group differences in salt preference were not due to changes in taste responsiveness. There were no differences between the groups in saline preferences in short-term tests or in the amplitudes of chorda tympani nerve responses to concentration series of several salts. The implications of these data for understanding the physiological basis for group differences in salt preference are discussed.

Animals↗
PubMed1986

Maternal dietary sodium chloride levels affect the sex ratio in rat litters.

Eighty-eight adult female rats were fed diets containing either 0.08, 0.12, 1, 3, or 4% NaCl for at least one week prior to breeding and throughout gestation. Within 24 hours of birth, all pups were sexed based on anogenital distance, and the number of males and females were recorded. The amount of sodium chloride in mother rats' diets was inversely related to the proportion of phenotypic males in the litter. As dietary salt increased, the proportion of males decreased. These alterations in dietary NaCl affected the sex ratio without disrupting litter size or the general health of the offspring. Dietary mineral content may affect the phenotypic sex ratio through changes in the genotypic sex ratio, or alternatively, via changes in the environment in which the genes are expressed. These findings are important for basic research concerning maternal nutrition and development.

Animals↗
PubMed1986

Dietary salt affects fluid intake and output patterns of pregnant rats.

This study was done to determine how differences in dietary NaCl influence water and electrolyte balance during gestation. Eighteen adult female rats were fed diets containing either 0.12 (low), 1.0 (mid, control), or 3.0% (high) NaCl throughout gestation. On gestation days 1-19, body weight, water and food intakes, urine volume and electrolyte levels were measured. On gestation day 20, amniotic fluid electrolyte levels were determined; litter sizes were assessed 24-hr after birth. Because food intakes were similar throughout gestation, the dams of the three groups ingested different amounts of NaCl. Differences in dietary NaCl were accompanied by large differences in the daily patterns of urine sodium, urine sodium/potassium ratios, water intake, and urine volume. Despite these differences in intake and output, water and electrolyte balance (intake minus output) was the same for the three groups. There were no differences in the dams' body weights, amniotic fluid electrolyte levels, or litter sizes. The long-term consequences of perinatal dietary NaCl for the developing pups are discussed.

Animals↗
PubMed1985

Behavioral and neural gustatory responses in rabbit.

To provide more information on a potentially valuable preparation for studies in taste and appetite, we have examined the taste preferences (and aversions) and chorda tympani sensitivity of the rabbit. Adult male New Zealand rabbits were given a two-bottle preference test between water and various molar concentrations of NaCl, KCl, sucrose, sodium saccharin, quinine hydrochloride and HCl. The rabbits exhibited the expected preferences for sucrose and aversions for quinine and HCl. Unexpectedly, however, the rabbits exhibited only a mild preference for NaCl, a stronger preference for KCl, and an aversion to sodium saccharin. Multiunit discharges of the chorda tympani nerve to the same taste stimuli indicated that the anterior tongue receptors are acutely sensitive to KCl, NaCl and quinine, but not to sucrose, HCl and saccharin. The chorda tympani was more responsive to KCl than to NaCl. Dilute concentrations of both NaCl and sodium saccharin elicited a two-component response consisting of an immediate excitatory phase followed by a tonic inhibitory phase. This complex response pattern of the whole nerve to NaCl and sodium saccharin is discussed in relation to the impulse frequencies in hypothesized water-sensitive and salt-sensitive fibers. Both the behavioral and neural data are discussed in relation to similar data obtained in rat and hamster.

Animals↗
PubMed1985

Adrenalectomy reduces peripheral neural responses to gustatory stimuli in the rat.

In the rat, sodium need leads to an increase in sodium intake, which depends on salt taste sensitivity. The adrenalectomized rat, because of excessive body sodium loss, has been an important animal model for studying the physiological mechanisms underlying salt ingestion. In order to investigate the mediation by peripheral taste responsivity of changes in salt intake, multiunit responses of the chorda tympani nerve to various concentrations of sodium chloride, potassium chloride, lithium chloride, hydrochloric acid, and quinine hydrochloride were recorded from adrenalectomized and control rats. In order to control for a generalized decrease in sensory sensitivity, recordings from the auriculotemporal nerve to tactile stimulation of the pinna were also performed. There were no group differences in amplitude of the integrated neural responses to tactile stimulation. The largest decrease in gustatory responsivity occurred for suprathreshold concentrations of sodium chloride and lithium chloride. The data are discussed with reference to possible mechanisms underlying this neural alteration and to the role that reductions in salt taste responsivity play in mediating increases in salt intake.

Adrenal Glands↗
PubMed1984

Area postrema: part of the autonomic circuitry of caloric homeostasis.

Investigations in which lesion techniques are used suggest a role for the area postrema (AP) in caloric homeostasis. Ablations of the AP in rat are associated with temporary hypophagia, hypodipsia, and rapid body weight loss. This is followed by a steady period of relatively normal eating and drinking and body weight gain. This steady period is characterized specifically by lowered body weight maintenance levels, overingestion of palatable foods, and attenuated taste aversion learning and glucoprivic feeding. These effects cannot be attributed simply to lesions of central terminations of gustatory and visceral afferents. The AP may be involved in feeding behaviors that are triggered by chemical signals in the blood or cerebrospinal fluid. In addition, the AP along with the adjacent nucleus tractus solitarii (NTS) seems to be part of the central autonomic system subserving caloric homeostasis; this system includes the lateral hypothalamus, which has a well-documented role in energy balance. The contribution of the AP along with the NTS must be considered with respect to their relationship to other structures within this system.

Animals↗
PubMed1983

Area postrema lesions disrupt food intake induced by cerebroventricular infusions of 5-thioglucose in the rat.

The present experiment assesses the contribution of the area postrema (AP) to glucoprivic feeding in the rat. Lateral ventricular infusions of 5-thioglucose increased pelleted food intake in sham animals but not in animals with AP lesions. Drinking in response to infusion of angiotensin II into the lateral ventricle was not reduced by AP lesions. The data suggest that the AP is part of the brainstem circuitry underlying glucoprivic feeding.

Animals↗
PubMed1983

Enhanced saline intake and decreased heart rate after area postrema ablations in rat.

The area postrema (AP) is a circumventricular organ located in the dorsal medulla. Previous studies found that AP lesions lead to increased saline ingestion in the rat. The salt appetite was thought to be a result of primary disruptions in sodium regulation or in cardiovascular regulation. To assess this we measured food and fluid intakes, urinary electrolyte and aldosterone concentration, and blood pressure and heart rates in AP lesioned and control animals during a period of normal sodium intake and during a period of excessive sodium intake. Rats with AP lesions exhibited sodium appetite but not natriuresis. In fact, sodium intake greatly exceeded output. Their urinary aldosterone levels were similar to those of control animals during both periods. The lesioned rats also had lowered heart rates, yet, their blood pressures were similar to control animals. These results are discussed with reference to a possible role of the AP in satiety and in maintaining homeostasis.

Aldosterone↗
PubMed1983

Prenatal and early postnatal sodium chloride intake modifies the solution preferences of adult rats.

To determine whether the concentration of sodium chloride (NaCl) consumed early in life influences the degree of NaCl preference later in life, adult female rats were maintained on diets containing either 0.12, 1.0, or 3.0% NaCl throughout pregnancy; their offspring were continued on these same diets to day 30 of life. Thereafter, all offspring were maintained on a diet containing 1.0% NaCl. At 90 days of age the animals were given a two-bottle preference test between water and various concentrations of NaCl, glucose, and KCl solutions. After preference testing the livers and adrenal glands were removed and weighed. Both male and female offspring raised on the high salt diet showed an elevated preference for NaCl solutions as adults. The effect was nonspecific as the males also exhibited an enhanced preference for glucose solutions. Furthermore, the elevated preferences could be accounted for not by increases in absolute NaCl or glucose intake, but by decreases in water intake. The adrenal gland weights were significantly lower for males in the highest salt group. There is an early period in development during which fluid regulation may be influenced permanently by dietary sodium levels.

Animals↗
PubMed1983

Nerve fibers sensitive to ionic taste stimuli in chorda tympani of the rat.

Hypotheses about the peripheral basis for the sense of taste in mammals have been based to a considerable degree on the determined sensibilities of the nerve fibers in the chorda tympani of the rat to chemical stimulation of the anterior tongue. Yet, whether neuron types exist in this nerve, the nature of the basic mechanisms of taste reception that are tapped by this nerve and the form in which information about stimulus quality and intensity is transmitted to the central nervous system by this nerve are, at present, unresolved issues. These issues are addressed in the present study, which is a detailed analysis of the responses of rat chorda tympani nerve fibers that are sensitive to ionic stimuli; solutions applied to the anterior tongue included a range of concentrations of four chemical compounds (sucrose, sodium chloride, hydrochloric acid, and quinine hydrochloride) that represent widely different taste qualities to man or rat. Of the 44 nerve fibers sampled, 40 were stimulated most by one of the two ionic stimuli at test concentrations reported to be equally effective: 21 fibers were most responsive to 0.1 M NaCl and named N units; 19 fibers were most responsive to 0.01 M HCl and named H units. Although many N and H units responded to both HCl and NaCl, the distribution of NaCl-HCl response ratios was bimodal, indicating there are two varieties of units sensitive to ionic taste stimuli in the rat chorda tympani. Sucrose (0.5 M) affected 4 of the nerve fibers and was the most effective stimulus for 3 of them; 0.02 M quinine affected 13 of the fibers but 10 of these were H units. H units were less "specifically tuned" than N units; they were more likely to respond to several of the chemicals. Although the absolute sensitivity to NaCl in N units or to HCl in H units varied more than 10-fold, the relative effects of the four stimuli (response profiles) were generally similar for units of a given type. Exceptions occurred when H unit responses to NaCl or quinine were suppressed by prolonged effects of preceding HCl stimulation. The similarity in response profiles is reflected in high and significant correlations between responses to each pair of effective stimuli across either H or N units.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1982

Area postrema lesions produce feeding deficits in the rat: effects of preoperative dieting and 2-deoxy-D-glucose.

To investigate the possible role of the area postrema (AP) in the control of food intake and body weight, male albino rats were divided into four groups: (a) animals dieted to 80% of their original body weights prior to receiving AP lesions, (b) nondieted animals with AP lesions, (c) animals dieted to 80% prior to receiving sham lesions, and (d) nondieted animals with sham lesions. Lesions of the AP in nondieted rats resulted in hypophagia, hypodipsia and body weight loss followed by recovery of normal intake and maintenance of body weight at a fixed percentage of the sham operated animals' weight. Reducing body weight prior to surgery led to body weight maintenance levels equivalent to those of the nondieted groups. We also tested the animals for sensitivity to glucoprivation caused by intraperitoneal injections of 2-deoxy-D-glucose (2-DG). Injections of 2-DG produced hyperphagia in sham lesioned rats, but not in rats with AP lesions. Our data suggest that the effects of AP lesions on intake and body weight are similar, in several important respects, to the lateral hypothalamic feeding syndrome and to the effects of subdiaphragmatic vagotomy. We discuss the results with respect to hierarchical levels of neural circuitry involved in controlling feeding behavior.

Animals↗
PubMed1982

The central projections of the trigeminal, facial, glossopharyngeal and vagus nerves: an autoradiographic study in the rat.

The central distributions of primary afferent axons in the facial, trigeminal (mandibular branch), glossopharyngeal, and vagal nerves of the rat have been re-examined using the autoradiographic tracing technique after injections of [3H]proline or [3H]leucine into their peripheral ganglia. Within the nucleus of the solitary tract (NST), the labeled terminals from VII, V, IX and X form a continuous distribution that spans the length of this nucleus. Sensory axons in VII terminate mainly within the lateral division of the rostral NST, although some of the terminals extend further caudally within the nucleus. Immediately caudal to the rostral NST, the distribution continues with major contributions from V and IX. Both are confined mainly to the lateral division of the NST, although some of the fibers in IX terminate within the medial division. Injections into the inferior ganglion of X confirm the extensive distribution of vagal axons as they ramify significantly within the lateral division, and virtually monopolize the medial division of the NST. Thus, the major zone of convergency for these 4 cranial nerves is the lateral division of the nucleus from the level of the entering fascicles of IX caudally to the level of the area postrema. Furthermore, only X has a crossed projection as vagal axons invade the commissural nucleus and the medial division of the contralateral NST. Vagal fibers also enter the area postrema bilaterally. Finally, some afferent fibers from VII, IX and X descend in the dorsal part of the spinal trigeminal tract and terminate within the marginal subdivision of the spinal trigeminal nucleus pars caudalis, as well as the dorsal horn of the cervical spinal cord.

Animals↗
PubMed1981

Changes in salt intake lesions of the area postrema and the nucleus of the solitary tract in rats.

Several reports have linked the area postrema (AP), a circumventricular organ in the dorsal medulla, to the control of sodium regulation. To clarify its role further we examined the effects of AP ablations in rats on sodium intake as well as on sodium output. Eighteen experimental rats received lesions to the AP while 6 control rats received sham lesions. After the lesions we gave the animals a two-bottle preference test between water and various molar concentrations of NaCl (0.03, 0.1, 0.3, 0.5), glucose (0.1, 0.3) or KCl (0.1, 0.3) solutions. Rats with AP lesions consumed supranormal amounts of NaCl solutions, but their intakes of glucose and KCl solutions were not significantly different from those of control rats. These changes in intake were apparently not secondary to changes in sodium output. Urinary sodium and potassium levels were the same for both groups of rats while on a normal, sodium-replete diet or on a sodium-free diet. Anatomical analyses revealed a significant correlation between the size of the lesion and the animals' salt intake (NaCl, KCl). Only when the lesions destroyed the AP without appreciable damage to the adjacent nucleus of the solitary tract (NST), a sensory relay for gustatory and visceral afferents, was there a significant tendency for rats to consume more salt solution. These changes in intake cannot be accounted for by lesioned produced deficits in gustatory function. The data were discussed with regard to possible hemodynamic effects of the lesions.

Animals↗