Origin of posterior pituitary high intensity on T1-weighted magnetic resonance imaging. Immunohistochemical, electron microscopic, and magnetic resonance studies of posterior pituitary lobe of dehydrated rabbits.
OBJECTIVE
To investigate the origin of posterior pituitary high intensity (PPHI) seen on T1-weighted magnetic resonance (MR) images.


METHODS
Six rabbits, including four rabbits deprived of drinking water for 4 days and two control rabbits, were examined by MR imaging. Plasma vasopressin levels were sequentially measured by radioimmunoassay. Pituitary glands were immunostained with guinea pig anti-rabbit vasopressin antibody, and ultrathin sections of Epon/Araldite-embedded specimens were observed with a transmission electron microscope.


RESULTS
In control rabbits, PPHI was noted on T1-weighted MR images, and the posterior pituitary lobe was positively immunostained with anti-vasopressin antibody. At the ultrastructural level, nerve terminals contained numerous neurosecretory granules bearing vasopressin. Conversely, plasma vasopressin levels gradually increased and PPHI was absent in 4-day dehydrated rabbits. The posterior lobe was scarcely stained with anti-vasopressin antibody, and neurosecretory granules were rarely observed. However, a number of small dispersed vesicles, possibly derived from the fragmentation of neurosecretory granule envelopes, were seen in the nerve terminal.


CONCLUSIONS
Posterior pituitary high signal seen on T1-weighted MR images is attributed to neurosecretory granules bearing vasopressin.
Sato
N
N
Department of Diagnostic Radiology, School of Medicine, Gunma University, Maebashi, Japan.
Tanaka
S
S
Tateno
M
M
Ohya
N
N
Takata
K
K
Endo
K
K
D000818:Animals; D003594:Cytoplasmic Granules / Q000648:ultrastructure; D003681:Dehydration / Q000097:blood / Q000473:pathology*; D004853:Epoxy Resins; D007089:Image Enhancement; D007150:Immunohistochemistry; D008279:Magnetic Resonance Imaging; D008297:Male; D008854:Microscopy, Electron; D009411:Nerve Endings / Q000648:ultrastructure; D009489:Neurosecretion; D010796:Phthalic Anhydrides; D010904:Pituitary Gland, Posterior / Q000473:pathology* / Q000648:ultrastructure; D016613:Plastic Embedding; D011817:Rabbits; D011863:Radioimmunoassay; D014667:Vasopressins / Q000032:analysis / Q000097:blood
D004853:Epoxy Resins; D010796:Phthalic Anhydrides; D014667:Vasopressins; C005752:araldite; C004875:EPON