Alterations in vasopressin regulation in Alzheimer's disease.

Abstract

A possible injury in the non-hormonal AVP system in Alzheimer's disease has been suggested by the recent finding of a reduced AVP concentration in CSF and in brain tissue.1-4 A decrease in plasma hormonal AVP has been also reported, suggesting damage as well to the hypothalamic magnocellular neurons and/or the neurotransmitters controlling the secretion of hormonal AVP.4The main mechanisms controlling hypothalamic AVP secretion"6 are changes in blood osmolality and decrease in blood pressure and/or blood volume. An increase in blood osmolality is sensed by the osmoreceptor sited in the anterior hypothalamus. Impulses are carried from osmoreceptors to vasopressinergic neurons along cholinergic pathways. A decrease in blood pressure stimulates the highpressure carotid baroreceptor which, in turn, releases AVP through noradrenergic and cholinergic pathways; impulses are carried by the glossopharyngeal nerves to the brain stem, nucleus tractus solitarius, locus coeruleus and paraventricular and supraoptic nuclei.6 Changes in blood volume act on the cardiopulmonary baroreceptors which stimulate AVP

Hypouricemia, Abnormal Renal Tubular Urate Transport, and Plasma Natriuretic Factor(s) in Patients with Alzheimer's Disease

“…It is highly unlikely, however, for the factor in AD to be atrial natriuretic peptide, brain natriuretic peptide, or urodilatin because, in contrast to the findings in the present study, they increase sodium excretion principally by increasing glomerular filtration rate, and they are associated with a decrease in blood pressure 22 – 25 . Antidiuretic hormone, which can induce a natriuresis in rats, is not a likely factor in AD because low plasma levels, probably resulting from defective ADH secretion, are typical of AD 26 – 28 . It is also unlikely for the natriuretic effect of plasma to result from any of the medications taken by the patients, any associated illness, or differences in diet or sodium intake.…”

Hyponatremia in a Nursing Home Population

“…The data suggest that patients with dementia of Alzheimer's disease may be at lower risk of hyponatremia than patients with other forms of CNS disease. Several studies indicate that vasopressin secretion may be diminished in patients with Alzheimer's disease, both under basal conditions 29 and following stimulation by pharmacologic agents 30–32 or by dehydration 33,34 . Thus, the vasopressin‐deficient state can allow ready excretion of water when patients with Alzheimer's disease are challenged by increased oral or intravenous fluids.…”

Vasopressin and thirst in patients with posterior pituitary ectopia and hypopituitarism

“…The infusion was discontinued when a decrease in mean arterial pressure (MAP) greater than 30 m mmHg was observed or when HR increased by more than 25 beats/minutes Two samples of venous blood for AVP, adrenalin and noradrenalin determination were drawn from a catheter placed in the controlateral arm during the last 15 minutes of the perfusion period and one during the eighth minute of each infusion period. Values were compared to normal values obtained in healthy controls by our group (Norbiato et al ., 1988).…”