Effect of Repeated and Prolonged Stress Stimuli on the Plasma Prolactin Concentration in Sheep

Summary

The effect of repeated and prolonged stress-stimuli applied during 3 days on the plasma prolactin concentration in sheep, in anoestrous, prooestrous and pregnant animals were studied. The following results were obtained:

1. Repeated and prolonged weak electric stimuli applied in the form of footshocks in sheep during 3 days elicited a rise of mesor plasma concentration. The magnitude and the onset of this rise was not associated and dependent on the physiological state of animals.

2. The mesor values of plasma prolactin concentration in all groups of animals except prooestrous ewes on the day following stimulation returned to their prestressing levels.

3. Repeated and prolonged stimuli disturbed circadian rhythm of prolactin secretion existing only in prooestrous ewes, i.e. they caused its disappearance on the days during stimulation and its reappearance on the day following stimulation but at an accelerated and inverse time of the day to that found before stimulation.

4. The induced rise of plasma prolactin concentration in anoestrous and pregnant ewes on the days during electric stimulation showed, according to Cosinor analysis, all features characteristic for acrophase of the circadian rhythm. This phenomenon may be considered as induced acrophase in stress condition.

Key words

Prolonged footshocks - Stress-prolactin secretion