1. Investigación

El ayuno de 48 h produjo en ratas, mantenidas en jaulas metabólicas, una disminución en la cantidad de agua bebida y aumento del volumen de orina excretada. Tanto la cantidad de creatinina como de urea excretada al dia disminuyeron con el ayuno, mientras que la de amoniaco aumentó. Ademas de demostrar la perdida de agua metabólica con el ayuno, los resultados indican que el principal producto de! catabolismo de aminoacidos con el ayuno es el amoniaco derivado del metabolismo de la glutamina en el riñón mas que la urea formada en el higado.

Suckling rats from 5 to 30 days of age were subjected to fasting in a 37° C chamber to avoid possible metabolic effects from low environmental temperature. The percentage of body weight loss in 24 h fasting increased along with the age of the rats. Blood glucose levels were the same in 5, 10, 20 and 30 day old animals when fed, whereas fasting produced a fall in all the groups which was minimal in the 20 day old animals. Plasma insulin levels were rather low in 10-day-old fed animals; the maximal decrease in this parameter was reached by 5-day-old rats under fasting. Both beta-hydroxybutyrate and acetoacetate levels were higher in animals of 5 and 1 0 days of age than in those of 30 days, but fasting did not produce any changes in the former while those parameters augmented in the 20 and 30-day-old animals. The results are discussed in relation to the high fat content in the mother's milk. which affects the metabolic situation of the suckling rats when fed and their response to the fasting situation.

The effect of glucose, arginine, pyruvate and palmitate administration on levels of circulating glucose and RIA-insulin was studied in fed and 48 h-fasted rats. The rise in blood glucose level after oral glucose load was greater in fasted than in fed rats, whereas plasma insulin level increase was similar in both groups. When glucose was given intravenously, plasma RIA-insulin rose only in the fed animals. Arginine administration produced minor changes in these parameters in both fed and fasted rats. Oral pyruvate produced greater enhancement in blood glucose concentration in fasted than in fed animals while plasma insulin levels rose only in the fed rats. After palmitate load, blood glucose levels increased only in the fed animals in which there was also an increase in plasma insulin levels following intravenous administration of fatty acid. These results suggest that none of the metabolites used except glucose has a physiological role in insulin secretion in the fed or fasted animals; in the latter group sensitivity to glucose stimulus was greatly reduced while the release of insulinotropic gastrointestinal factors after administration of oral glucose appeared less affected. The changes in blood glucose levels observed after addition of pyruvate or palmitate are discussed in terms of the role of pyruvate as a gluconeogenetic substrate and of the effect of palmitate on glucose metabolism.