AJP - Gastrointestinal and Liver Physiology, Vol 243, Issue 5 359-G364, Copyright © 1982 by American Physiological Society
Site of thyroxine-evoked decrease of jejunal lactase in the rat
J. T. Boyle, K. Kelly, L. Krulich and O. Koldovsky
Localization of thyroid-mediated decrease of lactase activity along the
villus-crypt unit in adult rat jejunum was studied 24 and 48 h after first
injection of L-thyroxine (200 micrograms/100 g body wt) every 24 h.
[3H]thymidine was also given at time of first thyroxine injection. Serum
thyroid-stimulating hormone, food intake, and body weight were
significantly decreased within 24 h. Total jejunal protein and villus-crypt
height were unchanged during the time period studied. Lactase activity
(expressed both as per tissue protein and per intestinal segment) was
significantly decreased in jejunum and midjejunum within 24 h. Serial
sectioning of the jejunal villus-crypt unit in a cryostat showed that the
site of decrease in lactase activity at 24 h was in the apical villus and
by 48 h extended along the entire height of the villus. Epithelial cell
migration measured both by histoautoradiography and scintillation counting
of [3H]thymidine in cryostat sections revealed no difference between
control and thyroid-treated animals at both 24 and 48 h. The decrease in
lactase activity at 24 h was in advance of the leading edge of
radioactivity, indicating that the thyroid-evoked response occurred in
mature enterocytes already on the villus.
