Plasma levels of atrial natriuretic peptide in hyperthyroidism

Plasma atrial natriuretic hormone in hyperthyroidism

In 22 hyperthyroid patients, atrial natriuretic hormone (ANH) levels (71.91 +/- 21.03 pg/ml), measured during a 3-h-Holter, were found to be significantly higher (p < 0.001) than those in 20 age-matched normal subjects (37.22 +/- 8.73 pg/ml). We have demonstrated that the presence of tachiarrhythmias does not influence ANH release. The positive and significant correlation of FT3 with both ANH and heart rate confirms the hypothesis of a direct action of thyroid hormones on ANH release.

Atrial natriuretic peptide and cyclic guanosine monophosphate plasma concentrations in patients with thyrotoxicosis and atrial fibrillation. Effect of short-term methimazole therapy

Plasma immunoreactive atrial natriuretic peptide (ANP) and cyclic guanosine monophosphate (cGMP), serum thyroxine (T4), triiodothyronine (T3), and thyrotropin (TSH) concentrations were measured in 11 patients with thyrotoxicosis and atrial fibrillation (group 1), in 5 patients with thyrotoxicosis and sinus cardiac rhythm (group 2) and in 8 healthy subjects in comparable age. Patients with thyrotoxicosis were studied before and after treatment with methimazole (3 x 20 mg daily) during 10 days. During treatment sinus cardiac rhythm returned in 6 patients with initial fibrillation (group 1a) while 5 patients still presented atrial fibrillation at the end of the study (group 1b). All patients from group 2 maintained a sinus cardiac rhythm throughout the study. Median plasma concentrations of ANP and cGMP before treatment in patients from group 1 were higher: 43.8 pmol/l and 11.0 nmol/l, respectively than in patients from group 2: 20.0 pmol/l (p < 0.005) and 6.5 nmol/l (p < 0.01), respectively. In all groups of patients methimazole treatment resulted in a significant decrease of plasma ANP and cGMP concentrations in parallel to a reduction of serum T3 and T4 levels. After therapy, plasma ANP and cGMP levels in patients from group 1a were not significantly different from those in patients from group 2, while in patients from group 1b remained slightly elevated. Presented results suggest that atrial fibrillation in patients with thyrotoxicosis represents an important factor augmenting plasma ANP and cGMP levels, in addition to the stimulatory effect exerted by thyroid hormones. However, the marked reduction of serum thyroid hormones produced by short-term methimazole treatment in patients with thyrotoxicosis was associated with parallel decrease of plasma ANP and cGMP levels toward normal values. Therefore, the influence of thyroid hormones on plasma ANP and cGMP concentrations seems relatively more important than the effect of atrial fibrillation.

Regulation of hepatic glycolysis and gluconeogenesis by atrial natriuretic peptide

Recently we reported the presence of both the guanylyl cyclase-linked (116 kDa) and the ANF-C (66 kDa) atrial natriuretic peptide receptors in the rat liver. Since ANF 103-125 (atriopeptin II) stimulates cGMP production in livers and because cGMP has previously been shown to mimic the actions of cAMP in regulating hepatic carbohydrate metabolism, studies were performed to investigate the effects of atriopeptin II on hepatic glycolysis and gluconeogenesis. Additionally, employing analogs of atrial natriuretic hormone [des-(Q116, S117, G118, L119, G120) ANF 102-121 (C-ANF) and des-(C105,121) ANF 104-126 (analog I)] which bind only the ANF-C receptors, the role of the ANF-C receptors in the hepatic actions of atriopeptin II was evaluated. In perfused livers of fed rats atriopeptin II, but not C-ANF and analog I, inhibited hepatic glycolysis and stimulated glucose production. Moreover, analog I did not alter the ability of atriopeptin II to inhibit hepatic glycolysis. Atriopeptin II, but not C-ANF and analog I, also stimulated cGMP production in perfused rat livers. Furthermore, while atriopeptin II inhibited the activity ratio of pyruvate kinase by 30%, C-ANF did not alter hepatic pyruvate kinase activity. Finally, in rat hepatocytes, atriopeptin II stimulated the synthesis of [14C]glucose from [2-14C]pyruvate by 50% and this effect of atriopeptin II was mimicked by the exogenously supplied cGMP analog, 8-bromo cGMP. Thus atriopeptin II increases hepatic gluconeogenesis and inhibits glycolysis, in part by inhibiting pyruvate kinase activity, and the effects of atriopeptin II are mediated via activation of guanylyl cyclase-linked ANF receptors which elevate cGMP production.

Atrial natriuretic factor in untreated hyperthyroidism

Increased plasma concentration of atrial natriuretic factor (ANF) in untreated hyperthyroid patients is reported. A significant positive correlation between the concentration of ANF and serum thyroid hormones (T4 and T3) has been found when hyperthyroid patients and healthy controls were pooled together. The mechanism by which thyroid hormones raise plasma ANF concentration and its relevance to the symptomatology of hyperthyroidism is discussed.

Induction of ventricular morphogenesis and atrial natriuretic factor synthesis by thyroid hormone

Thyroid hormones have been shown to increase atrial natriuretic peptide (ANP) synthesis in atria both in vitro and in vivo. In this study the effects of triiodothyronine (T3) administration on primary cultures of 6-day-old atrial and ventricular myocytes were studied. Levels of immunoreactive (ir-) ANP were determined by radioimmunoassay over 9 days of culture in cells cultured in the presence and absence of 10(-8) M T3. The proportion of immunostained nuclei was also determined and changes in cell characteristics noted over this time. Over 9 days T3 had no effect on the proportion of atrial cells immunostained for ANP, while cell and medium content of ir-ANP in treated wells doubled that of the untreated. In treated ventricular myocytes, cell and medium ir-ANP similarly increased; in addition, the proportion of immunostained cells increased by 1-2 orders of magnitude. The formation of dendritic processes was enhanced in these cultures, reflected in increased rates of spontaneous contractility. Thus it would appear that the 6-day-old myocardium exhibits profound differences in response to T3 administration, in that ventricular cells dedifferentiate and undergo morphological changes which are not seen in atriocytes.

Thyrotropin modulates receptors for atrial natriuretic peptide on intact human thyroid cells

Interest in the mechanism of impaired salt and water metabolism in hypothyroidism has led to growing evidence of an interaction between atrial natriuretic peptide (ANP) and the thyroid, which includes reports of direct effects of thyroid hormone on ANP synthesis and circulating ANP levels, and of the presence of specific ANP receptors in human thyroid tissue, which may act to inhibit thyroglobulin (Tg) secretion. The authors questioned whether or not thyrotropin (TSH) has a role in this interaction. They used 125I-ANP to study the effect of TSH on ANP binding to human thyroid cells in primary culture. Binding competition by increasing concentrations of unlabeled ANP in the presence or absence of TSH was assessed by Scatchard analysis. At lower temperatures of 4 degrees C or 23 degrees C, TSH had no effect either on the ANP receptor equilibrium dissociation constant (Kd) or number of binding sites. However, at 37 degrees C, bovine TSH at 1 mU/ml reduced measurable binding sites by about 50% without affecting receptor affinity (Kd = 0.2 nM). Prolonged (6 days) coincubation of TSH with thyroid cells decreased the assayable ANP receptor. The effects of TSH appear to be specific because human luteinizing hormone, follicle-stimulatory hormone, growth hormone, human chorionic gonadotropin and iodide had no effect on ANP binding. Thus, human thyroid cells possess a single class of high-affinity, specific receptors for ANP with binding activity that is temperature dependent and modulated by TSH at physiologic temperature. TSH-mediated reduction of binding at 37 degrees C but not at 4 degrees C suggests an energy-dependent process that acts possibly by activating an ANP degradative enzyme or by changing the rate of receptor internalization and subsequent degradation.

The effects of low dose intravenous 99-126 atrial natriuretic factor infusion in patients with chronic renal failure

The aim was to study the renal and hormonal effects of intravenous 99-126 atrial natriuretic factor (ANF) infusion in a mixed group of patients who had moderate to severe chronic renal failure (CRF) and who were not treated with dialysis. The peak mean plasma level of ANF achieved during the experiment was at the upper limit of an absolute range of basal values previously recorded in a larger group of patients with similar degrees of renal impairment. A significant tissue effect was confirmed by rises in plasma and urinary cyclic guanosine monophosphate, the 'second-messenger' of ANF. ANF infusion increased sodium excretion rate by a mean of 68% compared with a fall of 40% in a placebo group, and significant increases in urinary albumin excretion occurred during the peptide infusion. Thus, the high levels of plasma ANF found in CRF may have a role in the maintenance of sodium balance. In addition, the proteinuric effect may be detrimental to long-term renal function.

Nifedipine for epilepsy? A pilot study

Images