Effects of thyrotropin-releasing hormone and its analogue L-6-ketopiperidine-2-carbonyl-leucyl-L-prolin-amide on behaviour and electroencephalogram.

A comparative dose-response investigation of thyrotropin-releasing hormone (TRH) and L-6-ketopiperidine-2-carbonyl-leucyl-L-proline-amide (RGH-2202) was carried out on rats and cats. RGH-2202 reduced the occurrence of photically evoked after-discharge in rats more significantly than TRH. Neither of the two compounds influenced the parameters of visually evoked potentials. Both compounds desynchronized the background electrocortical activity in rats. The amplitude of the acoustic startle reflex in rats was decreased dose-dependently only by RGH-2202, and this effect was nearly 3 times more potent than that of TRH. Both compounds increased the time spent awake, the latency to light sleep and the proportion of light sleep in a dose-dependent manner. The higher doses of TRH equalled the effects of the lower doses of RGH-2202. In cats the latency increasing effect of TRH on paradoxical sleep was about 30% less than that of RGH-2202; furthermore, the relative increase in the proportion of light sleep coupled with a corresponding decrease of deep sleep and paradoxical sleep was significant only in the case of RGH-2202. In a complex conditioned reflex situation in cats, the dose-dependent motivation decreasing effect on food intake and, as a consequence, on spontaneous motor activity was more pronounced in the case of TRH. The effective doses of RGH-2202 and TRH in rats were nearly equal, while in cats RGH-2202 showed about 1/10 of the potency of TRH. This finding suggests a considerably lower species variability of the effects of RGH-2202.(ABSTRACT TRUNCATED AT 250 WORDS)