A comparative study of some possible mechanisms governing the intraluminal and intravascular release of 5-HT from the rabbitjejunum

Abstract

(Uncorrected OCR) Abstract

Abstract of thesis entitled "A comparative study of some possible mechanisms governing the intraluminal and intravascular release of 5-HT from the rabbit jejunum" submitted by WONG Joseph Chi-yan

for the degree of Doctor of Philosophy (Pharmacology) at the University of Hong Kong in April 1973.

Experiments were carried out on rabbit jejunal segments in. vivo and in vitro under conditions of intraluminal and intravascular perfusion. 5-HT was released into the effluent of both intraluminal- and intravascular perfusate during perfusion with Krebs solution under quiescent conditions. Enhanced 5-HT release was observed during active peristalsis elicited by increasing the intraluminalpressure during intraluminal perfusion. The addition of hydrochloric acid in physiological amounts

to give pH values of 7.2, 6, 5 and 4 in Krebs solution revealed a progressive increase in 5-HT release as the pH fell, during intraluminal perfusion. Enhanced 5-HT release was also observed during intraluminal perfusions with 0.3 M and 0.6 M sucrose solutions; 0.6 M glucose solution and 7.5% egg albumin in Krebs solution.

During intraluminal perfusion, Sennosides A &

BlO ~g/ml., Nicotine 1 ~g/ml. and Morphine 10 ~g/ml. in Krebs solution, all enhanced 5-HT release; but not 1% Monosodium L-glutamate. Monoamine oxidase inhibitor,

Nialamide, in a concentration of 100 ~g/ml. prevented . the destruction of both endogenous and exogenous 5-HT.

Nicotine 1 ~g/ml. and Morphine 10 ~g/ml. did not enhance 5-HT release during intravascular perfusion.

From the above observations, it is concluded that, in rabbits, 5-HT is involved in the normal physiological functions of digestion, absorption and motility. It possibly functions as a local hormone in regulating these processes. The intravascular release of 5-HT demonstrated in these experiments may not have any direct physiologic~l significance.

It is not appropriate to compare the two perfusion methods in terms of the net amount of released 5-HT. From histological observations, it is suspected that the results of intraluminal perfusion are complicated by the shedding off of intestinal epithelial cells, into the perfusing fluid. Further investigations are needed to evaluate the reliability of this method in the study of the phenomenon of 115-HT release II under such experimental conditions, and the interpretation which can be put upon the results obtained.

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