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Unlabelled: Correlations between meal size and inter-meal intervals as a characteristic of ingestive behavior are generally calculated utilizing Pearson's correlation coefficient. However, this commonly used method may exhibit disadvantages and methodological problems when dealing with dependent time series. Alternatively, a modified version of Pearson's r (r(diff)) or a nonparametric procedure, Pfanzagl's T combined with an expanded sampling theorem offer a statistical alternative for correlational analysis, robust to stochastic interdependencies between time series. In two studies, porcine self-initiated feeding behavior was observed in a closed economy setup, and a comparison of all three correlation coefficients was performed. STUDY 1: Twelve Munich mini-pigs were observed for 2 weeks. The rate of food ingestion was a stable characteristic of each individual pig, feeding and defecation behavior were temporally associated and light/dark cycle differences were seen for feeding. STUDY 2: Eight Munich mini-pigs were studied for 4 weeks. Kendall's Tau was utilized to test the stability of feeding behavior across weeks. Stability increased over time and feeding was more stable during the light period. Both correlation measures revealed a strong association between meal size and inter-meal intervals., Conclusion: Munich-miniature pigs exhibited a stable pattern of self-initiated ingestive and excretory behaviors. In both studies, Pfanzagl's T-values as well as r(diff)-values revealed a corresponding and consistent association between meal size and inter-meal intervals. In combination with the conventional Pearson's r, all three coefficients characterize different aspects of feeding behavior.

The long-term observation of ingestive and excretory behaviors in freely ambulating and non socially isolated pigs is an important tool in the investigation of the physiological determinants of these behaviors. A computer-controlled laboratory setup for the recording of feeding, drinking, and defecation behavior in minipigs was developed, allowing for the observation of two pigs at a time for weeks. Four minipigs (29-52 kg) were conditioned to operate feeders with a precise food release per response and were then fed ad lib. The animals had up to 50% of their daily energy intake during the night. Meal size and time spent eating was highly correlated, meal size and the preprandial intermeal interval was moderately correlated, whereas meal size and the postprandial intermeal interval was not. Feeding facilitated defecation, supporting the assumption that the gastrocolonic response is present in the pig. The system has been shown to be highly reliable and valid, and thus provides an excellent tool for the investigation of the rhythmicity of ingestive and excretory behaviors in minipigs.

Chronic changes in rectal compliance and perception are often associated with constipation, but the mechanisms responsible for these changes are not known. These studies evaluated the dynamic response of the rectal wall to distention and, in a separate investigation, the influence of adaptive relaxation on perception thresholds. In Study 1, seven healthy volunteers were evaluated using a computer-controlled barostat to maintain continuous isobaric distention of the rectum at urge threshold over a 25-min period. Changes in intrabag volume were evaluated at minutes 1, 5, and 25. Study 2 investigated changes in perception thresholds with different interstimulus intervals (30 s vs. 60 s) in 16 healthy subjects. Pressure was incremented in steps of 2 mmHg up to discomfort threshold. The mean intrabag volume, pressure, and the compliance index for the first and second 5-s intervals were compared to the last 5 s interval. Statistical analyses were performed using the Wilcoxon Sign-Rank test with Bonferonni corrections. Study 1 showed a significant relaxation of the rectal wall in response to balloon distention with volumes consistently increasing from minute 1 to minute 25. Study 2 showed a significant change in the compliance index at the threshold for moderate urge and intense urge during the 60-s distention that resulted from progressive relaxation of the rectal wall. Study 1 showed an adaptive response of the rectum to distention. Study 2 confirmed these findings and implied a role for this adaptive response in the determination of rectal sensory thresholds.

To determine the effect of nutrient ingestion on rectal perception thresholds (first sensation, consistent urge to defecate, pain), rectosigmoid balloon distentions were performed with a computerized automated pump in eight healthy volunteers (four males, four females, 31.6 +/- 6.02 years). Two measurements of rectal balloon distention were performed on 2 separate days. Day 1 served as a control condition with no meal. On day 2 the subjects received a 600 kcal liquid meal. On the control day, determination of perception thresholds was performed two times with a 10-min break between measurements. On the experimental day, threshold determinations were made before and after the ingestion of the liquid standard meal. The order of the experimental days was counterbalanced. Distention volumes at the urge to defecate and the pain threshold (maximum tolerable volume) were significantly reduced following the meal. The average change from pre- to postprandial measurements of the threshold for urge to defecate was -20.55 +/- 4.22% and for the maximum tolerable volume it was -16.09 +/- 4.4%. These results extend data previously reported from animal studies using similar experimental methods.

The effects of eating and rectal distention on cecal tone were evaluated. Cecal tone was measured using a computer-controlled barostat in four female 30 to 40 kg Yucatan Micropigs fitted with cecal fistulas. Each pig underwent two separate trials of pre and postprandial measurements of cecal tone, either with or without continuous rectal distention with a 30 ml water-filled balloon. Cecal tone was measured 10 min prior to, during, and 10 min following a high-fat (60%) liquid meal (473 ml). Cecal tone significantly increased (intrabag volume decreased) after feeding (119.6 +/- 9.1 ml vs. 81.2 +/- 7.9 ml; p = 0.008). Rectal distention tended to reduce the postprandial change in cecal tone (142.8 +/- 11.5 vs. 130.9 +/- 12.6 ml; p = 0.196). There was also a strong tendency for cecal volumes to be higher (decreased tone) with rectal distention preprandially (142.8 +/- 11.5 ml vs. 119.6 +/- 9.1 ml; p = 0.024). Nutrient ingestion significantly increased cecal tone and rectal distention abolished this effect. These findings may indicate a regulatory pathway that allows additional storage of fecal material in the event that the output of the system is disturbed.

The effect of atropine on defecation threshold was compared to placebo pre- and postprandially in four 20- to 30-kg pigs. Stepwise balloon distention was performed 10 cm from the anal verge with a 5-cm latex balloon. Volume was increased in steps of 10 ml up to 200 ml of air or until the balloon was defecated (defecation threshold). Dependent measures were balloon volume, rectal pressure, rectal compliance, and an index of distention-induced contractile activity. Under placebo conditions, the volume and pressure to elicit defecation were significantly lower after feeding (p < 0.05). The distention-induced contractile activity significantly increased near the defecation threshold, but pre- and postprandial conditions were not different. No differences were seen between pre- and postprandial rectal compliance curves. Atropine abolished the postprandial decrease in defecation threshold, but did not affect rectal compliance. The increase in contractile activity at defecation threshold seen with placebo was abolished by atropine. These results show that eating lowers the defecation threshold in terms of distention volume and rectal pressure, and demonstrate that these changes are mediated through cholinergic pathways.

The effect of prolonged (6 h), continuous rectal distention on mouth-to-cecum and colonic transit time was studied in four unrestrained pigs. Mouth-to-cecum transit time was determined from samples of cecal efflux using the phenol red dye technique. Colonic transit time was assessed with radiopaque markers that were injected into the cecum before each trial. Rectal distention was applied 2-1/2 h before feeding, during feeding, and 3-1/2 h after feeding. No distention was applied during control conditions. Stools were collected for 48 h after marker application. Rectal distention increased mouth-to-cecum transit time (p < 0.05). Colonic transit time was also prolonged by rectal distention as shown by a significant decrease in the number of markers excreted within 36 h (p < 0.05). Rectal distention for 6 h increased colonic transit time up to 30 h following distention and prolonged mouth-to-cecum transit of a high fat liquid meal.

The aim of this study was to develop a chronic model suitable for repeated, long-term studies of the interaction of behavior and colonic function in unrestrained pigs. Cecostomies were created in three 20-30 kg micropigs under general anesthesia. Fistulas were created by suturing the bowel to the abdominal wall. Recordings were made by passing a small (8F) solid-state pressure transducer through the fistula into the proximal bowel and connecting it to a battery-operated data logger worn in a vest on the pig's back. Cecostomies have remained patent and trouble-free for over 18 months. No serious infections have occurred. Preliminary data from a total of thirteen 24-h recording sessions showed 54% of all contractile activity to be in the 2-4 cpm frequency range. Increased motility was seen following meals and upon morning awakening. Motility was minimal during the night. Infrequent (10.31 +/- 2.05/24 h; mean +/- SD) propagated contractions were also noted. These contractions were generally of low amplitude (33.24 +/- 3.81 mmHg). These techniques allow prolonged, intraluminal recordings to be made from the colon of the unrestrained pig.

The effect of eating on defecation behaviour was investigated in four 20-30 kg pigs. Rectal distention stimulation was performed pre- and postprandially at 10 cm from the anus with a 5 cm latex balloon. Volume was increased in steps of 10 ml up to 200 ml of air or until balloon defecation. Dependent measures were volume, rectal pressure, determined with a solid state pressure transducer inside the balloon probe, rectal compliance, and an index of distention induced contractile activity. The volume and pressure required to elicit defecation was significantly lower after feeding (p less than 0.01). Distention induced contractile activity was significantly increased near defecation threshold, but pre- and postprandial conditions were not different. There was no difference in rectal compliance pre- and postprandially. These results suggest that eating lowers defecation threshold in terms of distention volume and rectal pressure, and that these changes are not dependent on altered rectal compliance or changes in distention induced motor activity.