EDITORIAL SYNOPSIS In the intact animal some observers have shown an increased absorption of sugars and fatty acid after treatment with thyroxin. The following paper, in which uptake studies on the small isolated intestine of rats made thyrotoxic are reported, shows that inhibition of absorption of water, glucose, and a non-utilizable amino-acid (ac-amino isobutyric acid) can also result. The authors feel that the estimation for these differences may be because of differences of doses of thyroxine, methods of administration, and possibly a variable effect of different tissues.Hyperthyroidism is well known clinically to bring about emaciation and gastrointestinal disorders.Recently it was shown in many animals, such as rats, guinea-pigs, rabbits, and dogs, and also in frogs, that there is a reduction in the gastric acid secretion when these animals were fed with desiccated thyroid (Nasset, Logan, Kelley, and Thomas, 1959;Goldsmith and Nasset, 1959;Nasset and Goldsmith, 1961). Accelerated uptake of glucose in the intact intestine of hyperthyroid rats has been reported (Althausen, 1949; Althausen and Stockholm, 1938), while it has been claimed that thyroxine increases glucose absorption from the perfused gut of Rana esculenta (Gellhorn and Northup, 1933).The effect of thyroidal hormones on the absorption processes of the isolated intestine do not, however, appear to have attracted much attention. Halliday, Howard, and Munro (1962) have shown that glucose transfer across the isolated everted intestine of mice was inhibited when the animals were fed with 0 5 % desiccated thyroid for 14 days (personal communication), but that there was no change in the water movement across the gut; Levin and Smyth (1963) have also observed that hyperthyroid rats show little change in their hexose transfer mechanism across the isolated intestine. Very recently one of us (Seshadri, in preparation) has obtained results to show that thyroxine can produce inhibitory effects on the oxygen consumption and phosphorylation of the intestinal segments of rats. The present work reports the effect of thyroxine on the absorption and movement of non-utilizable amino-acid, o-amino isobutyric acid, glucose, and water by the isolated rat intestine.
MATERIALS AND METHODSFemale rats of about 200 g. body weight were given intraperitoneal injections of 100 ,ug. Na-thyroxine in physiological saline (0-9% NaCl) per 100 g. of body weight daily for three days. Control rats received only normal saline solution. Rats were killed by ether on the fourth day following 18 hours of starvation. The entire intestine was washed in situ with cold saline as soon as the viscera were opened. The ilial portion, from the posterior end of the duodenum up to the caecum was removed, everted, and divided into five equal portions. Three of the intestinal segments (I, II, and ILI) from the duodenal end were prepared following the technique of Wilson and Wiseman (1954) as modified by Parsons, Smyth, and Taylor (1958) for longer pieces of gut. Each segment was made into a sac, tyi...
