MEDIAL SEPTAL-LESIONS - BODY-WEIGHT LOSS AND ITS RELATIONSHIP TO POLYURIA IN RATS

Changes in body weight in relation to water intake and urine output were examined in male rats bearing medial septal lesions. Medial septal ablation resulted in an alteration in urinary secretion which was paralleled by an alteration in body weight. Immediately following surgery body weight dropped. Over the remainder of the observation period body weight increased at a normal rate; however, the animals bearing medial septal lesions never recovered to the level of the sham operated group. Immediately following medial septal ablation there was a marked increase in urine output. Urine volume subsequently declined but remained elevated in relation to control animals throughout the 3 weeks of observation. When isotonic saline was substituted for drinking water, body weight, fluid intake and urine volume increased with both groups; however, the body weight increase was less pronounced in the medial septal animals as a result of a higher level of urine excretion than sham operated animals. Food intake, fecal output, rectal temperature, and urine pH were also examined, but appeared to have no bearing on the weight loss, either following surgery or during saline ingestion. On the basis of these results it was suggested that the medial septal nucleus, in response to increases of blood osmolarity, normally facilitates the activity of hypothalamic structures responsible for the secretion of pituitary anti-diuretic hormone. © 1979.