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Biomedical subjects

T R Houpt

Publications and source records attributed to T R Houpt.

At least 19 recordsLinked to original sources
PubMed2000

Effect of water restriction on equine behaviour and physiology.

Six pregnant mares were used to determine what level of water restriction causes physiological and/or behavioural changes indicative of stress. Nonlegume hay was fed ad libitum. During the first week of restriction, 5 l water/100 kg bwt was available, during the second week 4 l/100 kg bwt and, during the third week, 3 l/100 kg bwt. Ad libitum water intake was 6.9 l/100 kg bwt; at 3 l/100 kg bwt water intake was 42% of this. Daily hay intake fell significantly with increasing water restriction from 12.9 +/- 0.75 kg to 8.3 +/- 0.54 kg; bodyweight fell significantly for a total loss of 48.5 +/- 8.3 kg in 3 weeks. Daily blood samples were analysed; osmolality rose significantly with increasing water restriction from 282 +/- 0.7 mosmols/kg to 293.3 +/- 0.8 mosmols/kg bwt, but plasma protein and PCV did not change significantly. Cortisol concentrations fell from 8.1 ng/ml to 6.4 ng/ml over the 3 week period. Aldosterone fell from 211.3 +/- 74.2 pg/ml to 92.5 +/- 27.5 pg/ml at the end of the first week. The behaviour of 4 of the 6 mares was recorded 24 h/day for the duration of the study. The only significant difference was in time spent eating, which decreased with increasing water restriction from 46 +/- 3% to 30 +/- 3%. It is concluded that water restriction to 4 l/100 kg bwt dehydrates pregnant mares and may diminish their welfare, but is not life- or pregnancy-threatening.

Animals↗
PubMed1999

A rapid feedback signal is not always necessary for termination of a drinking bout.

When a pig is deprived of drinking water, a deficit of body water develops that is corrected when the pig drinks to satiation. If food is available during the deprivation, the stimulus to drinking is plasma hyperosmolality. Because of the delay in correction of plasma hyperosmolality as ingested water is slowly absorbed, it has been thought that a rapid inhibitory signal from the digestive tract is necessary to prevent overdrinking. This concept was tested by measuring changes in plasma osmolality before and during drinking after such deprivation and also after infusion of hypertonic saline. As drinking began, there was a rapid fall of plasma osmolality to levels insufficient to drive drinking by the time drinking ended. This fall of plasma hyperosmolality to subthreshold levels while the pig is drinking seems to make a rapid inhibitory control signal from the digestive tract unnecessary to terminate the drinking bout under these conditions.

Animals↗
PubMed1995

Water deprivation, plasma osmolality, blood volume, and thirst in young pigs.

When deprived of both drinking water and food, pigs failed to develop the hyperosmolality usually expected with dehydration. In further studies 12 pigs were deprived of drinking water and food, and the effects were compared with data from nondeprived pigs, pigs water deprived but with food available, and pigs with water but no food. When food was eaten during water deprivation, plasma osmolality rose to levels sufficient to stimulate drinking. During water and food deprivation, plasma osmolality failed to rise, even over 24 h, and usually fell. Blood volume changes were calculated from packed cell volume and plasma protein data, and it was found that blood volume fell significantly when both food and water were withheld, but not when only water was withheld. It appears that the conditions of deprivation determine the proportions of thirst stimulation that can be attributed to plasma hypertonicity and to hypovolemia.

Animals↗
PubMed1994

Gastric pressures in pigs during eating and drinking.

Pressures were measured with miniature transducers positioned within the gastric lumen of six young pigs, 20-40 kg, eating and drinking operantly. The pigs were free to move about, lie down, sleep, eat, and drink without disturbance. 1) At the end of 4-5-h fasts (with no drinking), mean pressure within the stomach was 12 cm H2O, then rose during 22-min eating bouts to 22 cm H2O. 2) At the end of 16-18-h periods of food and water deprivation, intragastric pressure was 9 cm H2O. When water was drunk, pressures rose only to 13 cm H2O, then fell. When food was then eaten, pressures rose during 29-min meals to 22 cm H2O. 3) During spontaneous eating and drinking, intermeal pressures were maintained at 22-25 cm H2O, fell by 4-5 cm H2O just as eating or drinking began, then rose slowly, but only to the preingestive pressure level by the end of the bout. These results indicate that during spontaneous eating and drinking, gastric distention per se plays a smaller direct role in causing satiety than it does during meals ingested after a period of food deprivation.

Afferent Pathways↗
PubMed1992

The mechanism and significance of pentagastrin-stimulated water intake in the pig.

The role of gastric secretion in drinking was investigated. Treatment of pigs with cimetidine (300 mg IV), which inhibits gastric secretion, did not change the level of feed or water intake, or alter the temporal relationship between eating and drinking. Gastric infusions of 0.15 M HCl (5 ml.kg-1.h-1) did not increase drinking. Pentagastrin infusion (0.05 microgram.kg-1.min-1) increased water intake in some, but not all pigs during a 1-hour infusion. Plasma protein levels increased significantly during 1-hour pentagastrin infusions (0.05 microgram.kg-1.min-1), indicating an estimated fall in blood volume of 2.5%. Captopril (1.75 mg/kg IV), which blocks the renin-angiotensin system, abolished pentagastrin-stimulated drinking. It was concluded that gastric secretion does not play a direct role in normal, periprandial drinking but that in pigs the renin-angiotensin system is involved in pentagastrin-stimulated drinking.

Animals↗
PubMed1991

Patterns of duodenal osmolality in young pigs fed solid food.

Duodenal hypertonicity can induce satiety, but whether duodenal osmolality varies during eating enough to influence meal size is not clear. To find out more about this, duodenal samples were taken via implanted catheters from 10 young pigs under three feeding conditions. 1) The pigs were fasted 4-5 h and then given a meal with drinking water available. Duodenal osmolality rose from a premeal level of 297 mosmol/kgH2O to a peak of 430 mosmol/kgH2O at 35 min after the meal began and then returned to the premeal level after 2.2 h. 2) When pigs were similarly fasted and then given a meal, but with no drinking water available during and after the meal, osmolality rose to 418 mosmol/kgH2O after 35 min and only returned to premeal levels after 4.2 h. 3) Finally, when pigs were allowed to eat and drink spontaneously, osmolality rose from a mean of 281 to only 308 mosmol/kgH2O after meals, in part because of water drinking in association with meals and in part because the spontaneous meals were smaller. The results demonstrate that duodenal osmolality can rise significantly after meals but that hyperosmolality is moderated by water drinking.

Animals↗
PubMed1991

Thirst and salt appetite in horses treated with furosemide.

When a preliminary experiment in sodium-replete ponies revealed an increase, but not a significant increase, in salt consumption after furosemide treatment, the experiment was repeated using sodium-deficient horses in which aldosterone levels might be expected to be elevated to test the hypothesis that a background of aldosterone is necessary for salt appetite. Ten Standardbred mares were injected intravenously with furosemide or an equivalent volume of 0.9% sodium chloride as a control to test the effect of furosemide on their salt appetite and blood constituents. Sodium intake and sodium loss in urine, as well as water intake and urine output, were measured and compared to determine accuracy of compensation for natriuresis and diuresis. Plasma protein and packed cell volume showed significant increases in response to furosemide treatment (F = 29.31, P less than 0.001 and F = 11.20, P less than 0.001, respectively). There were no significant changes in plasma sodium concentration or osmolality in response to the treatment (P greater than 0.05). The furosemide-treated horses consumed 126 +/- 14.8 g salt, significantly more than when they were given the control injection (94.5 +/- 9.8 g; t = 2.22, P = 0.05). In response to furosemide, horses lost 962 +/- 79.7 and consumed 2,170 +/- 5 meq sodium; however, compared with control, they lost 955 meq more sodium and ingested only 570 meq more sodium, so they were undercompensating for natriuresis. The furosemide-treated horses drank 9.6 +/- 0.8 kg of water, significantly more than when they received the control injection (6.4 +/- 0.8 kg; t = 6.9, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Spontaneous drinking: is it stimulated by hypertonicity or hypovolemia?

Ten young female pigs were allowed to eat and drink whenever they wanted, and blood samples were taken without disturbance to the pig. Samples were divided into four categories: 1) base line, i.e., taken when not drinking and not eating; 2) preprandial, i.e., taken when starting to drink just before eating; 3) postcibal, i.e., taken when starting to drink after any eating; and 4) nonprandial, i.e., taken when starting to drink but not in association with eating. Osmolality (mosmol/kgH2O), plasma protein (g/dl), and packed cell volume (%) were, respectively, as follows (mean +/- SE): base line 294.9 +/- 1.8, 6.2 +/- 0.1, and 30.0 +/- 1.2; preprandial 295.1 +/- 1.7, 6.1 +/- 0.2, and 29.7 +/- 1.4; postcibal 295.0 +/- 3.3, 6.5 +/- 0.2, and 31.7 +/- 1.3; and nonprandial 295.2 +/- 1.4, 6.3 +/- 0.1, and 30.0 +/- 1.3. None of the parameters associated with drinking were significantly different from base-line parameters, except for the postcibal rise of packed cell volume. Calculated blood volume differences from base line were as follows: preprandial 0.7 +/- 1.2% fall; postcibal 0.2 +/- 1.7% increase; and nonprandial 0.8 +/- 0.9% fall. It is unlikely that either plasma hypertonicity or hypovolemia stimulates drinking under spontaneous conditions.

Animals↗
PubMed1990

Hypertonic and hypovolemic stimulation of thirst in pigs.

Young female pigs weighing from 15 to 45 kg were used. Plasma osmolality was slowly raised by an intravenous infusion of 15% NaCl. The behavioral threshold was when the pigs began to drink water, and the rise of osmolality was the stimulus. In 23 measurements on 8 pigs the rise of osmolality to initiate drinking was 10.4 +/- 1.4 mosmol/kg (mean +/- SE). There was also an estimated 3.8 +/- 1.4% rise of blood volume. Control infusions of 0.9% NaCl for 1 h usually resulted in no drinking, and plasma osmolality fell by 6.7 +/- 2.1 mosmol/kg, while blood volume did not change. Hypovolemia was effected using furosemide (1 mg/kg body wt) to cause excretion of nearly isotonic urine. Blood volume changes were estimated from plasma protein and packed cell volume data. In 28 measurements on 6 pigs, drinking occurred when blood volume had decreased by 6.7 +/- 1.8%. During 2-h control periods, blood volume did not change appreciably. Plasma osmolality decreased during both the furosemide treatment (by 3.5 +/- 0.7 mosmol/kg) and the controls (by 4.1 +/- 0.8 mosmol/kg).

Animals↗
PubMed1989

Stimuli of thirst in donkeys (Equus asinus).

A study of the stimuli of thirst was conducted on six feral donkeys. Donkeys were found to be stimulated to drink by overnight water deprivation, by the diuretic furosemide, and by hypertonic saline infusion, all in the absence of heat stress or work. Donkeys compensate accurately for the fluid deficit caused by overnight water deprivation. After 19 hr without water, they drank 8.8 +/- 2.4 (mean +/- SE) liters within 60 min. Their undeprived overnight intake was 8.4 +/- 1.5 liters. However, latency was longer and water intake was less than that of ponies with the same changes in blood parameters, suggesting that donkeys have a higher thirst threshold than ponies. Further, plasma volume fell less in donkeys, but osmotic changes were similar to those reported in ponies exposed to the same deprivation. Donkeys infused with 250 ml of 15% NaCl drank 0.7 +/- 0.6 liters of water within 45 min, and osmolality increased from 287 to 297 mosmol/kg water; they drank no water in the same time period when infused with 250 ml 0.9% NaCl (p less than 0.05). Donkeys injected IV with 2 mg/kg furosemide drank 3.8 +/- 1.1 liters within 3 hr. Plasma protein increased from 6.9 to 7.8 g/dl. When injected with 0.9% NaCl they drank 1.0 +/- 0.5 liters (p less than 0.05). In sum, the positive thirst responses of these donkeys to cellular and extracellular dehydration were similar to those earlier demonstrated in ponies, but the results suggest a less sensitive response, albeit combined with a better internal defense of blood volume.

Animals↗
PubMed1988

Feeding and drinking patterns in young pigs.

Feeding and drinking patterns of six immature female pigs, weighing from 10 to 130 kg, operantly obtaining feed and water at a fixed ratio of 10, were determined. It was found by log survivorship analysis that 10 min was the minimum interbout interval defining separate eating bouts. As the pigs grew through this weight range, daily feed intake increased nearly threefold, while eating bout frequency fell from 14 to 7 per day; consequently both eating bout size and interbout interval increased. However, bout size was increased primarily by an increased rate of eating during bouts without any consistent increase in bout duration. Neither premeal nor postmeal intervals were correlated with meal size. Of the pigs' daily water intake, 75% was closely associated with eating bouts and over 1/3 of this (25%) was preprandial. Sixty-four percent of daily food intake and 68% of water intake was during the 12-hr light period. Nocturnal eating bouts were less frequent, but larger.

Animals↗
PubMed1988

Effect of meal frequency on fluid balance and behavior of ponies.

Twelve ponies were fed their total daily ration either as one large meal or divided into six small meals. Pre- and post-feeding behavior was recorded six times a day. Blood samples were taken for 30 min before and two hr after the meal. Plasma protein increased from 7.0 to a peak of 7.3 g/dl with small meals and from 7.3 to 8.1 g/dl with large meals, and returned to pre-feeding levels by 90 min post-feeding. Hematocrit rose from 33.3 to 34.1% with small meals and from 33.0 to 36.0% with large meals. These rapid and short-lived increases indicate a decrease in plasma volume. Plasma osmolality rose with feeding from 283 to 285 mosmoles/kg with small meals and from 281 to 288 mosmoles/kg with large meals. Water availability had no significant effect on blood changes. Digestibility and rate of passage were measured with chromic oxide, but there were no differences. Vocalizing (neighing) and walking occurred more often before than after feeding, while eating bedding and engaging in other oral behaviors were more frequent after feeding.

Animals↗
PubMed1986

Water drinking induced by gastric secretagogues in pigs.

Eleven young pigs, feeding and drinking operantly, were tested for drinking responses to three gastric secretagogues. First, feed was removed for 1 h before the test period, then a continuous intravenous infusion of saline or a secretagogue was begun at a priming rate of 0.6 ml/min for the first 10 min, then at 0.3 ml/min for 50 min. Dose rates were the smallest that would still cause a vigorous gastric secretion. When 0.9% NaCl was infused, the pigs drank a mean of 54 +/- 11 (SE) ml. The comparable volumes for the secretagogues were histamine 174 +/- 41 ml (1 microgram . kg-1 . min-1); pentagastrin 231 +/- 38 ml (0.5 microgram . kg-1 . min-1); and bethanechol 231 +/- 35 ml (1.0-1.5 microgram . kg-1 . min-1). Pretreatment with cimetidine (300 mg iv) depressed the drinking response to histamine to 30 +/- 10 ml and to pentagastrin to 58 +/- 24 ml. Atropine (2 mg iv) depressed the response to bethanechol to 28 +/- 16 ml. Differences between responses to the secretagogues and either control drinking or antagonist-blocked responses were all significant (P less than 0.001). The results indicate that gastric secretion could play a role in stimulation of preprandial water drinking.

Analysis of Variance↗
PubMed1985

The effects of caloric dilution on meal patterns and food intake of ponies.

In order to determine if horses will increase their intake in response to caloric dilution, four pony geldings were fed ad lib a mixed grain diet either undiluted (3.4 Mcal/kg of digestible energy) or diluted (wt/wt) with 25% sawdust (2.6 Mcal/kg) or with 50% sawdust (1.7 Mcal/kg). The mean daily caloric intake was 17,457 kcal (3.4 Mcal diet), 17,546 kcal (2.6 Mcal diet) and 12,844 kcal (1.7 Mcal). The mean time spent eating was 246 (3.4 Mcal), 351 (2.6 Mcal), and 408 (1.7 Mcal) minutes/day. Meal size increased and meal frequency decreased with increasing dilution. The median long survivorships of intermeal intervals were 6.4 min (3.4 Mcal), 3.95 min (2.6 Mcal) and 4.91 min (1.7 Mcal). Ponies responded to caloric dilution by increasing the volume of intake to maintain caloric intake when the diet had 25% diluent. When the diet was diluted by 50%, intake was increased, but not at a rate adequate to maintain caloric intake. However, the ponies were able to maintain body weight.

Animals↗
PubMed1985

Humoral, hormonal and behavioral correlates of feeding in ponies: the effects of meal frequency.

The effect of meal frequency on body fluid, glucose, triiodothyronine (T3), heart rate and behavior was measured in 10 ponies. A simple reversal design was used in which each pony received one meal/day (1X) for 2 wk and six meals/day (6X) for 2 wk. The total intake/day was held constant. Feeding was followed by a rise in plasma levels of glucose, T3, protein and osmolality. One large meal was followed by significantly greater changes in all of the variables than was a meal one-sixth the size. Plasma T3 rose from 41 +/- 5 (SE) ng/liter before feeding to 43 +/- 5 ng/liter following a small meal, but rose significantly higher, from 39 +/- 4 to 60 +/- 10 ng/liter, following a large meal. Glucose rose from 84 +/- 3 to 109 +/- 7 mg/dl following a small meal and rose significantly higher, from 83 +/- 3 to 154 +/- 11 mg/dl, after a large meal. Plasma protein rose from 6.55 +/- .14 to 6.62 +/- .16 g/dl following a small meal and from 6.45 +/- .14 to 6.99 +/- .11 g/dl following a large meal. Osmolality rose from 227 +/- 1 mosmol/liter before to 279 +/- 1 mosmol/liter following a small meal and significantly higher from 278 +/- 2 to 285 +/- 1 mosnol/liter following a large meal. Heart rate rose from 42 beats/min in the absence of feed to 50 beats/min when food was visible to the ponies and did not rise higher when eating began. There were no significant differences in the cardiac response to one large meal and that to a small meal.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Controls of feeding in pigs.

The physiological controls of feeding behavior in pigs are reviewed. Feeding patterns, central nervous system integration of the control systems and the influence of taste and olfaction are briefly considered, but the emphasis of the review is on the specific control systems that determine meal size. The glucostatic mechanism of stimulation of eating operates in the pig, but is probably an emergency control in response to a severe deficiency of glucose available to the central nervous system. The effective controls determining meal size are predominantly inhibitory signals initiated within or near the gastrointestinal tract by the presence of food. There is evidence that a rise in osmoconcentration caused by the arrival of foodstuffs in the duodenum during a meal can inhibit feeding behavior to a degree proportional to the hypertonicity of the duodenal content. Arrival of chyme in the duodenum will also trigger the release of cholecystokinin (CCK). Exogenous CCK injected by various routes inhibits feeding, suggesting that endogenous CCK acts as a satiety or inhibitory signal during meals. Gastrointestinal distention during meals probably also acts as an inhibitory signal, but only preliminary studies have been made to delineate the role of this factor in feeding behavior. It is concluded that although considerable research has been conducted to reveal what control mechanisms operate in pigs, even the mechanisms already investigated are not firmly established as operating in normal meals. The osmoreceptive, CCK and gastrointestinal distention control systems are promising hypotheses worthy of further study, and the search for other control systems that may also participate continues.

Animals↗
PubMed1983

Effects of duodenal osmotic loads on spontaneous meals in pigs.

Fourteen young Large White pigs were trained to press a panel switch to obtain reinforcements of food (FR 10-15). Duodenal injections (5 ml/kg) were made automatically via implanted catheters shortly after the beginning of every other meal 24 hours a day. Solutions of varying osmoconcentration and nutrient content were injected. Isosmotic solutions of glucose (5, 20 and 40%) and NaCl (0.9, 3.25 and 6.5%) equally depressed the size of ongoing meals in proportion to their hypertonicity. For example, 20% glucose and 3.25% NaCl depressed meal size to 62% of control, and 40% glucose and 6.5% NaCl to 34%. Xylose (33%) was less effective than its glucose osmotic equivalent. Tetracaine (0.5%) blocked most of the reduction of meal size. The reduced meal size was due to a decrease in meal duration. Neither rate of eating during the meal nor intermeal interval changed. The results support the hypothesis that a duodenal osmoreceptive system participates normally in the control of meal size.

Animals↗