[Effects of dehydration of the pituitary microcirculation in rats].

The contiguous three lobe of the pituitary gland have different endocrine functions and vascular bed. This study was designed to investigate the effects of dehydration, which stimulates the secretion of vasopressin, on the pituitary microcirculation. Male Sprague-Dawley rats, weighing 300-380 g, were divided into two groups. Twenty three rats were allowed free access to food and water, and 24 rats had free access to food but were deprived of water for 5 days. Capillary solute transfer (K), plasma volume (Vp) and erythrocyte volume (Ve) in each pituitary lobe were determined for both control and dehydrated rats. Quantitative autoradiographic techniques were used to measure the K with 14C-alpha-aminoisobutyric acid (AIB, a small neutral amino acid), the Vp with 125I-albumin and the Ve with 51Cr-erythrocytes. Body weight was lower (-23%) and the arterial hematocrit was higher (+22%) in the dehydrated rats. In the lobes of the control pituitary gland, the order of K from the highest to the lowest was posterior much greater than anterior greater than intermediate lobe. K was increased by several folds only in the posterior lobe in dehydrated rats (p less than 0.05). Even under normal hydrated conditions, K for AIB in the posterior lobe was several hundreds times greater than in cerebral gray matter structures. The rank of Vp and Ve in each lobe of normal animals was about the same order and anterior greater than posterior much greater than intermediate. Normal microvascular Vp in the anterior and posterior lobes was 5-10 times larger than in cerebral gray matter.(ABSTRACT TRUNCATED AT 250 WORDS)