Effects of an Acute Water Load on Plasma ANP and AVP, and Renal Water Handling in Hypothyroidism: Comparison of Before and After L-Thyroxine Treatment.

Abstract

Abstract. To assess whether atrial natriuretic peptide (ANP) and arginine vasopressin (AVP) participate in impaired water excretion in patients with hypothyroid states (HS), an oral acute water loading (WL) test (20 ml/kg.BW/45 min) was performed before and after L-thyroxine (T4) treatment in 5 hypothyroid patients. Plasma ANP, AVP, osmolality (Posm), total protein and renal water excretion were simultaneously determined, and these data were compared to the data from five normal subjects (NS). The impaired water excretion rate in HS was entirely improved in the euthyroid states (ES) after T4 therapy for at least 7 months. Plasma ANP in HS was lower than that in NS (5.9± 0.9 vs. 16.5 ± 3.6 pmol / L, P<0.05), but increased after T4 treatment (21.2±5.7 pmol / L, P<0.05). Plasma AVP in HS (1.6± 0.5 pmol / L) showed a tendency to be lower than those in ES and NS (2.9 ± 0.4 and 2.9 ± 0.7 pmol / L), but did not respond to a fall in Posm after WL, unlike ES and NS. Significant positive correlation were noticed between Posm and plasma AVP in ES and NS, but not in HS. These results suggest that not only the impaired release and/or metabolisms of AVP and ANP, but also derangement of renal water and electrolytes handling might induce attenuation of CHZO formation in hypothyroid states.

Water metabolism disturbances at different stages of primary thyroid failure

“…In addition, our results suggested the integrity of the PRA-aldosterone axis. Most studies detect a decrease in the elimination of a water loading in hypothyroid patients, (DeRubertis et al 1971, Skowsky & Kikuchi 1978, Laczi et al 1987, Iwasaki et al 1990, Ota et al 1994) and a lower plasma osmolality than euthyroid individuals (Laczi et al 1987, Iwasaki et al 1990, Barna et al 1994, Ota et al 1994.…”

“…Levels of this hormone have been reported to be high in some hypothyroid patients, mimicking the state of inappropriate antidiuretic hormone secretion syndrome (SIADH) (Skowsky & Kikuchi 1978, Laczi et al 1987. However, more recently, plasma AVP has been found to be normal or low in hypothyroid patients (Iwasaki et al 1990, Ota et al 1994. In addition, low plasma levels of atrial natriuretic hormone (ANH) have been found in some studies (Kohno et al 1987, Zimmerman et al 1987, Woolf & Moult 1988, Vesely et al 1989, Widecka et al 1990, Barna et al 1994, Ota et al 1994.…”

“…However, more recently, plasma AVP has been found to be normal or low in hypothyroid patients (Iwasaki et al 1990, Ota et al 1994. In addition, low plasma levels of atrial natriuretic hormone (ANH) have been found in some studies (Kohno et al 1987, Zimmerman et al 1987, Woolf & Moult 1988, Vesely et al 1989, Widecka et al 1990, Barna et al 1994, Ota et al 1994. This decrease could influence the sodium and water regulation of patients with hypothyroidism, although its exact contribution remains undefined.…”

Potential Mechanisms of Hypothyroidism-induced Hyponatremia

“…Onthe other hand, plasma ADHhas been shown to be low, and ADHresponses to changes in plasma osmolality are attenuated in hypothyroidism (3, 7). In particular, Ota et al (3) showed that plasma ADHis decreased in hypothyroidism, but it did not decrease in response to a fall in plasma osmolality after an acute water load. These findings strongly suggest that there is impaired osmoregulation of ADHrelease and/or a decrease in the metabolic clearance rate (MCR)ofADH.…”

“…These difficulties might be mainly due to the multiplicity of the pathophysiology in hypothyroidism, involving impaired renal and cardiovascular functions as well as distortion of hypothalamo-adrenal systems , antidiuretic hormone (ADH)and atrial natriuretic peptide (ANP) release, which play important roles in water and electrolyte metabolisms (2,3). In hypothyroidism, decreases in free water formation and urine volume, especially following an acute water load, were consistently noticed, irrespective of the presence or absence of hyponatremia (3). Diminished ability of the kidney to excrete free water fails to produce maximumurine dilution, leading to water retention with consequent hyponatremia.…”