Gastroduodenal resistance and neural mechanisms involved in saline flow decrease elicited by acute blood volume expansion in anesthetized rats

Abstract

We have previously demonstrated that blood volume (BV) expansion decreases saline flow through the gastroduodenal (GD) segment in anesthetized rats (Xavier-Neto J, dos Santos AA & Rola FH (1990) Gut, 31: 1006-1010. The present study attempts to identify the site(s) of resistance and neural mechanisms involved in this phenomenon. Male Wistar rats (N = 97, 200-300 g) were surgically manipulated to create four gut circuits: GD, gastric, pyloric and duodenal. These circuits were perfused under barostatically controlled pressure (4 cmH 2 O). Steadystate changes in flow were taken to reflect modifications in circuit resistances during three periods of time: normovolemic control (20 min), expansion (10-15 min), and expanded (30 min). Perfusion flow rates did not change in normovolemic control animals over a period of 60 min. BV expansion (Ringer bicarbonate, 1 ml/min up to 5% body weight) significantly (P<0.05) reduced perfusion flow in the GD (10.3 ± 0.5 to 7.6 ± 0.6 ml/min), pyloric (9.0 ± 0.6 to 5.6 ± 1.2 ml/min) and duodenal (10.8 ± 0.4 to 9.0 ± 0.6 ml/min) circuits, but not in the gastric circuit (11.9 ± 0.4 to 10.4 ± 0.6 ml/min). Prazosin (1 mg/kg) and yohimbine (3 mg/kg) prevented the expansion effect on the duodenal but not on the pyloric circuit. Bilateral cervical vagotomy prevented the expansion effect on the pylorus during the expansion but not during the expanded period and had no effect on the duodenum. Atropine (0.5 mg/kg), hexamethonium (10 mg/kg) and propranolol (2 mg/kg) were ineffective on both circuits. These results indicate that 1) BV expansion increases the GD resistance to liquid flow, 2) pylorus and duodenum are important sites of resistance, and 3) yohimbine and prazosin prevented the increase in duodenal resistance and vagotomy prevented it partially in the pylorus.

Variations in gastric emptying of liquid elicited by acute blood volume changes in awake rats

“…This appears to be a more reasonable explanation since it is supported by our previous studies (4,5,7,8), and reinforced by a recent observation that duodenal motility is increased by BV expansion in anesthetized dogs (7). We have also verified that the gastric fundus, as well as the duodenum may actively participate in the GE delay due to BV expansion (8,9), but the possible pyloric participation cannot be completely excluded (8,9).…”

“…Firstly, we have observed that gastric and jejunal compliances are decreased by BV expansion while they are increased by BV retraction in anesthetized dogs (2,3). In addition, utilizing a barostatically perfused system, we have observed that BV changes also modify the gastroduodenal resistance to saline flow in anesthetized dogs: BV expansion increases the resistance of the gastroduodenal segment to the flow of liquid while retraction decreases it (4,5,8).…”

Neural mechanisms involved in the delay of gastric emptying of liquid elicited by acute blood volume expansion in awake rats

“…Since the greatest GE delay we observed in our previous studies was obtained in rats submitted to a BV expansion equivalent to 5% body weight, 9 we fixed this level of BV expansion in the present study in order to investigate the neural mechanisms involved in the GE delay elicited by acute BV expansion. This protocol has been extensively utilized in previous studies 6 , 8 –10 and did not increase immediate mortality.…”

“…infusion (Fars 600 pump, Lifemed, São Paulo, SP, Brazil) of Ringer‐bicarbonate solution (Na + = 140, K + = 4, Cl − = 124, HCO 3 − = 20 mmol.l −1 , 1 mL.min −1 , volume of 5% of body weight). This BV overload protocol has been extensively utilized in our previous studies, both in anaesthetized rats and in awake rats 6 . 8 –10 For investigating neural mechanisms, separate groups of rats were previously submitted to a drug pretreatment or a surgical procedure.…”

“…The gut seems to react to acute blood volume (BV) imbalances by adjusting the gastrointestinal (GI) motility 1 –10 as well as its permeability to fluid and electrolytes 11…”