[Appraisal of ultradian components in the ethosecretogram of rat]

An ethosecretogram, which illustrates phase relation between animal's behavior and plasma hormone levels, was constructed in conscious rats. A catheter was placed into the right atrium in male rats at least 2 days prior to blood sampling. Plasma corticosterone levels were monitored individually through the catheter every 5 min over a period of several hours under freely moving conditions on an Animex which records spontaneous locomotor activity. Furthermore, phase relation of ultradian components in both variables were analyzed in separate series of experiments. Results obtained are as follows; Both locomotor activity and plasma corticosterone level in the ethosecretogram exhibited ultradian components with a 60-90 min cycle. Ultradian components of both variables were phase-locked, the bursts of locomotor activity preceding the hormone peak by 15 min. As to the type of locomotor activity, feeding and grooming were significantly correlated with a subsequent hormone elevation, whereas drinking was not. Feeding-induced hormonal elevation was greater in response at dark phase (especially at midnight) than at light phase. Drinking of glucose solution induced a hormone elevation similar to feeding, whereas intravenous infusion of glucose solution did not. Feeding-induced hormone elevation was not abolished even when the vagi were effectively cut at a subdiaphragmatic level. It was assumed that the information from digestive organs to the CNS was not transmitted neurally via the sensory vagal nerves, but humorally via a humoral factor(s) released from digestive organs.