Evidence for thyroxine transport by the lung and heart capillary endothelium
The uptake and transport of carrier-bound thyroxine by the endothelium were investigated by perfusing through the heart and lung of young rats radiolabeled thyroxine bound to prealbumin ((125I)T4Pa) or serum ((125I)T4S). In addition these complexes were tagged to 5-nm gold particles to obtain quantitative (radioassay) and qualitative (autoradiography) data from the same experiment. The complexes (prewarmed at 37 degrees) were perfused in situ at various concentrations (1 to 50 muCi/ml) for time intervals ranging from 5 to 30 min. After thorough washing of the unbound probe, tissue fragments were either measured for total uptake in a gamma counter or processed for electron microscopy autoradiography. The results showed that both the lung and heart take up (125I)T4 complexes by a process that is saturable at low hormone concentration; uptake is completed by free T4 and Pa. In specimens perfused with double-labeled complexes (iodinated and tagged to gold) autoradiography revealed that silver grains and gold particles colocalize predominantly on endothelial plasmalemmal vesicles. The probe appeared first in vesicles open to the capillary lumen (5 min) and further on in vesicles apparently free within the cytoplasm or open to the abluminal front. At 30 min, only silver grains seem to be present in the pericapillary space, on the alveolar epithelial cells, as well as on the nucleus and mitochondria of heart myocytes. The findings suggest that (1) T4Pa uptake by the endothelial cell (EC) is a specific process (possibly via specific binding sites); (2) T4Pa is taken up and transported across capillary EC by plasmalemmal vesicles; (3) in the pericapillary space T4 seems to dissociate from its carrier.
- Research Organization:
- Institute of Cellular Biology and Pathology, Bucharest (Romania)
- OSTI ID:
- 5934455
- Journal Information:
- Microvasc. Res.; (United States), Journal Name: Microvasc. Res.; (United States) Vol. 37:2; ISSN MIVRA
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
ALBUMINS
AMINO ACIDS
ANIMAL TISSUES
ANIMALS
AUTORADIOGRAPHY
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BLOOD VESSELS
BODY
CAPILLARIES
CARBOXYLIC ACIDS
CARDIOVASCULAR SYSTEM
COLLOIDS
COMPLEXES
DISPERSIONS
ELECTRON CAPTURE RADIOISOTOPES
ELECTRON MICROSCOPY
ENDOTHELIUM
GOLD ISOTOPES
HEART
HORMONES
INTERMEDIATE MASS NUCLEI
IODINE 128
IODINE ISOTOPES
ISOTOPES
LUNGS
MAMMALS
MEMBRANE TRANSPORT
MICROSCOPY
MINUTES LIVING RADIOISOTOPES
MUSCLES
MYOCARDIUM
NUCLEI
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC IODINE COMPOUNDS
ORGANS
PEPTIDE HORMONES
PERFUSED ORGANS
PERMEABILITY
PROTEINS
RADIOASSAY
RADIOISOTOPES
RATS
RESPIRATORY SYSTEM
RODENTS
THYROID HORMONES
THYROXINE
TISSUES
VERTEBRATES