Jrv. Graca et al., GASTRODUODENAL RESISTANCE AND NEURAL MECHANISMS INVOLVED IN SALINE FLOW DECREASE ELICITED BY ACUTE BLOOD-VOLUME EXPANSION IN ANESTHETIZED RATS, Brazilian journal of medical and biological research, 30(10), 1997, pp. 1257-1266
We have previously demonstrated that blood volume (BV) expansion decre
ases saline flow through the gastroduodenal (GD) segment in anesthetiz
ed rats (Xavier-Neto J, dos Santos AA & Rola FH (1990) Gut, 31: 1006-1
010). 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 circ
uits: GD, gastric, pyloric and duodenal. These circuits were perfused
under barostatically controlled pressure (4 cmH(2)O). Steady-state cha
nges in flow were taken to reflect modifications in circuit resistance
s during three periods of time: normovolemic control (20 min), expansi
on (10-15 min), and expanded (30 min). Perfusion flow rates did not ch
ange in normovolemic control animals over a period of 60 min. BV expan
sion (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 (1
0.8 +/- 0.4 to 9.0 +/- 0.6 ml/min) circuits, but not in the gastric ci
rcuit (11.9 +/- 0.4 to 10.4 +/- 0.6 ml/min). Prazosin (1 mg/kg) and yo
himbine (3 mg/kg) prevented the expansion effect on the duodenal but n
ot on the pyloric circuit. Bilateral cervical vagotomy prevented the e
xpansion effect on the pylorus during the expansion but not during the
expanded period and had no effect on the duodenum. Atropine (0.5 mg/k
g), hexamethonium (10 mg/kg) and propranolol (2 mg/kg) were ineffectiv
e on both circuits. These results indicate that 1) EV expansion increa
ses the GD resistance to liquid flow, 2) pylorus and duodenum are impo
rtant sites of resistance, and 3) yohimbine and prazosin prevented the
increase in duodenal resistance and vagotomy prevented it partially i
n the pylorus.