Posterior lobe of the pituitary gland: correlation between signal intensity on T1-weighted MR images and vasopressin concentration.

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Abstract
PURPOSE: To correlate the signal intensity on magnetic resonance (MR) images in the posterior lobe of the pituitary gland with the vasopressin content. MATERIALS AND METHODS: Fourteen rabbits were studied: 12 water-deprived rabbits (two each at 48, 74, 96, 120, 144, or 168 hours of deprivation) and two control rabbits. Sagittal T1-weighted MR images were obtained before and after water deprivation. The signal intensity ratio of the posterior lobe to the pons was correlated with the vasopressin content in the posterior lobe, which was measured by means of radioimmunoassay. RESULTS: Before water deprivation, high signal intensity in the posterior lobe was demonstrated clearly in all rabbits. The signal intensity ratio and vasopressin content in the posterior lobe gradually decreased with water deprivation. The signal intensity ratio correlated strongly with the vasopressin content in the posterior lobe (Pearson correlation coefficient, .809; P < .001). CONCLUSION: The signal intensity ratio on T1-weighted MR images may be used as an indicator for the quantitative evaluation of the vasopressin content in the posterior lobe. The results strongly suggest that the origin of the high signal intensity in the posterior lobe on T1-weighted MR images is the vasopressin-neurophysin II-copeptin complex.

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