Effect of Neonatal Thyroidectomy, Age and Sex on Intestinal Absorption and Tolerance of Orally Administered Glucose in the Rat

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Abstract
Oral glucose tolerance was decreased in rats thyroidectomized at birth when compared with normal rats of comparable size (25 days old) or age (75 and 115 days). Thyroidectomized rats absorbed glucose per unit body size more slowly than normals of like size, but equally as fast as normals of the same age. Motility of the gastrointestinal tract was normal in absence of the thyroid. These tests in thyroidectomized rats, with one possible exception, were not affected by minute amounts of thyroid remnants which were capable of stimulating body weight gain, and to a lesser degree, development of gonads and skeleton. The total amt. of glucose absorbed by normal rats increased with size and age until the body weight exceeded 180 g., after which there was no change. There was an inverse relation with body size when the intestinal absorption rate was expressed as the amt. absorbed/100 g. body wt. The higher and shorter glucose tolerance curve, observed in young animals, could be related to a faster absorption rate. There was no effect of sex on intestinal absorption of glucose in normal rats when animals of similar size were compared. Similarly, the sex difference in the oral glucose tolerance test, only observed in 115-day-old rats, was related to size difference. It is suggested that the effects of age and sex on oral glucose tolerance, intestinal absorption and gastrointestinal motility in normal rats were secondary to their effect on body size.