Effect of immobilization and of elevation of the 5-hydroxytryptamine concentrations in the brain stem on liver tryptophan pyrrolase activity in a hibernator [the golden hamster
Novotná, R.
Physiologia Bohemoslovaca 30(1): 27-33
1981
ISSN/ISBN: 0369-9463 PMID: 6452635 Document Number: 178217
The effect of immobilization on liver tryptophan pyrrolase activity (LTP) in a hibernator, the golden hamster was studied. Since LTP is an inductive enzyme activated by corticosteroids, changes in its activity give indirect information on changes in the endocrine activity of the adrenal cortex in immobilization stress. Immobilization (2-3 h) did not stimulate LTP activity. LTP activity during immobilization and the next 3 h was non-significantly lower than in controls. Unchanged LTP activity of golden hamsters after immobilization was indirect evidence that the secretory activity of the adrenal cortex, did not alter or that corticosteroid output actually fell. Immobilization stress did not affect the activity of the hamster's pituitary-adrenal regulatory system directly, so that the response of a hibernator (the golden hamster) differed from the stress reaction of non-hibernating mammals to immobilization. An increase in brain 5-hydroxytryptamine (5-HT) concentration, pharmacologically induced by i.p. injection of its precursor, D,L-5-hydroxytryptophan or by a pargyline block of monoaminooxidase (MAO), non-significantly reduced LTP activity; the pharmacologically induced increase in brain 5-HT level was not sufficient to activate the pituitary-adrenal system. Administration of D,L-5-hydroxytryptophan at an environmental temperature of +20.degree. C produced a series of other, physiologically significant, changes. Only 5 min after injection a decrease in motor activity and a drop of up to 2.5.degree. C in body temperature were recorded. Intensive muscular tremor was observed at the same time and the animals slept continuously throughout the whole experiment. These effects depended on the dose of D,L-5-hydroxytryptophan. Large doses produced stronger effects of longer duration; doses of 100 mg/kg body mass and over were sometimes lethal. Parmacological elevation of 5-HT concentration in the CNS was not sufficiently selective. As well as affecting the regulation of pituitary function, it also modified other physiological functions controlled by 5-HT pathways in the brain.