Chris J. Winters

Two new hormones: Prohormone atrial natriuretic peptides 1–30 and 31–67 circulate in man

Two peptides consisting of amino acids 1-30 and 31-67 of the N-terminal end of the prohormone of atrial natriuretic factor (pro ANF) which vasodilate aortas in vitro, lower blood pressure in vivo, and have natriuretic properties were found to circulate in 54 normal human volunteers. The mean circulating concentration of pro ANF 1-30 was 1861 +/- 87 pg/ml (SEM) while pro ANF 31-67 mean concentration was 1478 +/- 71 pg/ml versus a level of 67 +/- 3 pg/ml for atrial natriuretic factor (ANF). In chronic renal failure their mean concentrations increased to 40,484 +/- 6,929 pg/ml (SEM), 108,566 +/- 16,888 pg/ml, and 348 +/- 81 pg/ml for pro ANFs 1-30 and 31-67 and ANF respectively. Since pro ANF 1-30 and pro ANF 31-67 circulate in man and have physiologic effects they meet the criteria of two new hormones.

Increased Release of the N-Terminal and C-Terminal Portions of the Prohormone of Atrial Natriuretic Factor During Immersion-Induced Central Hypervolemia in Normal Humans

Abstract The role of peptides from the N terminus and C terminus of the 126 amino acid atrial natriuretic factor (ANF) prohormone in modulating renal sodium and water handling has not been defined. Since water immersion to the neck (Nl) provides an acute central volume expansion identical to that produced by 2 liters of saline but without plasma compositional change, immersion to the neck was used to assess the N-terminal and C-terminal portions of the ANF prohormone response to acute central blood volume expansion in seven seated sodium-replete normal subjects. Both the C terminus, which contains amino acids 99– 126 and is identical to ANF, and the whole N terminus (i.e., amino acids 1–98) increased promptly with Nl and peaked after 1 hr of immersion. A M, 3900 peptide from the midportion of the N terminus consistent with amino acids 31–67 (i.e., pro-ANF-31–67) also increased with Nl and followed a pattern of increasing circulating concentration nearly identical to that of the whole N terminus of the prohormone, except that its maximal concentration was at the second hour of the 3 hr of Nl. With cessation of immersion, ANF decreased to preimmersion levels within 1 hr whereas the N terminus and pro-ANF-31–67, although their circulating concentrations were decreasing, were still significantly elevated at 1 hr. These findings suggest that the increase in plasma ANF, the N terminus of the ANF prohormone, and pro-ANF-31–67 from the midportion of the N terminus, with natriuretic properties similar to ANF, contribute to the natriuretic response to Nl, implying a physiologic role for these atrial peptides in modulating volume homeostasis in humans.

Circadian rhythm of prohormone atrial natriuretic peptides 1-30, 31-67 and 99-126 in man.

Two peptides consisting of amino acids 1-30 and 31-67 of the N-terminal end of the prohormone of the atrial natriuretic factor (pro ANF), vasodilate aortas in vitro, lower blood pressure in vivo, and have natriuretic properties similar to the atrial natriuretic factor (ANF, amino acids 99-126 of the prohormone). It has been recently discovered that pro ANF 1-30 and pro ANF 31-67 as well as ANF circulate in man. To determine if these three peptide hormones have a circadian variation in their circulating plasma concentrations, eight housestaff volunteers were studied on a day when they were in the hospital for 24 hr. These 5 men and 3 women, ages 25 to 39 had blood samples taken at 0800, 1200, 1600, 2000, 0000, 0400 and 0800 on the following day. One-half of these house officers were up all night while the other half went to sleep from midnight to 0800 and had their 0400 plasma samples drawn while in a supine position. The peak level for all three peptide hormones was at 0400 for both supine and upright subjects. It was concluded that there are circadian rhythms in normal, active people of these three peptide hormones, whose peak levels are at 0400 irrespective of posture.

Prohormone atrial natriuretic peptides 1–30, 31–67, and 99–126 increase in proportion to right ventricular pacing rate

To determine whether heart rate contributes to release of three new peptide hormones synthesized in the heart, right ventricular pacing at rates of 100, 125, 150, and 180 bpm was performed in six dogs with measurement of the plasma concentration of these peptides at each pacing rate while right atrial and systemic blood pressures were simultaneously monitored. These three peptides of the 126-amino-acid prohormone of atrial natriuretic factor (ANF), consisting of amino acids 1-30 (pro ANF 1-30), 31-67 (pro ANF 31-67), and 99-126 (ANF), increased incrementally at paced heart rates of 125, 150, and 180 bpm (r = 0.8, p less than 0.001). Right atrial pressure decreased with increasing heart rate but systemic blood pressure did not decrease until the heart rate was 180 bpm, at which time these peptides had obtained their maximal circulating concentrations. After pacing, mean right atrial pressure and levels of ANF returned to prepacing values within 30 minutes. Mean arterial blood pressure, on the other hand, increased throughout the 120-minute period after pacing. At 2 hours after pacing, levels of pro ANFs 1-30 and 31-67 were elevated compared with prepacing values. These data demonstrate that, at heart rates of 125 bpm and above, pro ANF 1-30, pro ANF 31-67, and ANF (99-126) are simultaneously and incrementally released in direct proportion to heart rate. The sustained elevation in pro ANFs 1-30 and 31-67 seen 2 hours after pacing suggests that they may contribute to the prolonged diuresis seen after cardiac pacing or tachycardia.

Prohormone atrial natriuretic peptides 1-30 and 31-67 increase in hyperthyroidism and decrease in hypothyroidism

Hyperthyroidism characteristically has natriuresis and vasodilation associated with it, whereas hypothyroidism is associated with impaired water excretion and vasoconstriction. This investigation was designed to determine if the plasma concentration(s) of three newly described hormones synthesized in the heart are increased in patients with hyperthyroidism and/or decreased in patients with hypothyroidism compared to normal subjects. The three hormones consist of amino acids 1–30, 31–67, and 99–126 (ANF) of the 126 amino acid prohormone of atrial natriuretic factor. Prohormone atrial natriuretic peptides (pro ANFs) 1–30, 31–67, and ANF were increased threefold, fourfold, and twofold respectively in hyperthyroid patients compared to the mean circulating concentration of 54 healthy persons without thyroid disease. Plasma concentrations of the three peptides in hypothyroid patients were only one-half that of the 54 persons without thyroid disease. With appropriate treatment of hyperthyroidism and hypothyroidism, the levels of the three peptides returned to normal. The peptide hormones increased proportionately with the increasing dosages of L-thyroxine of 50 μg/day and 100 μg/day in the hypothyroid patients. In persons with hypothyroidism complicated by congestive heart failure, the levels of pro ANFs 1–30, 31–67, and 99–126 were increased, demonstrating that abnormalities of salt and water metabolism are a strong stimulus to the release of these peptides.

Acute and sustained release of atrial natriuretic factor with acute myocardial infarction

The present investigation was designed to determine if acute ischemic cardiac injury causes the release of atrial natriuretic factor (ANF). Seventeen patients with acute myocardial infarction but without clinical evidence of congestive heart failure had their circulating concentration of ANF and creatine phosphokinase monitored daily for 14 days. All 17 patients had an elevated plasma ANF concentration at time of presentation. Maximal increase in ANF was on day 2 and 3 post-infarction. This maximal increase correlated with the size of infarction estimated by the maximal creatine phosphokinase concentration (r = 0.475; p less than 0.05), but did not correlate with the amount of left ventricular dysfunction. ANF began to decrease by day 4 post-infarction and was normal at 10 days post-infarction in 14 of the 17 (82%) patients. At 12 days post-infarction, all 17 patients had normal ANF levels. Another three patients with acute myocardial infarction were treated with tissue plasminogen activator (tPA). The measured ANF levels in these patients were within our normal range and were significantly lower (p less than 0.001) than those seen in patients with acute myocardial infarction not given thrombolytic therapy. Six patients with unstable angina likewise had normal circulating ANF concentrations during prolonged episodes of chest pain. These levels were also significantly lower (p less than 0.001) than the 17 patients with acute infarcts not given tPA. The distinct pattern of release of ANF may be useful as an adjunct to serum cardiac enzymes in determining if a myocardial infarction has occurred.

Pharmacokinetic Characterization of the Postdistribution Phase of Prohormone Atrial Natriuretic Peptides Amino Acids 1–98, 31–67, and Atrial Natriuretic Factor During and After Rapid Right Ventricular Pacing in Dogs

Release rate constants and disappearance rate constants were determined for three atrial natriuretic peptides consisting of amino acids 1–98 (i.e., proANF 1–98), the midportion of the ANF prohormone consisting of amino acids 31–67 (i.e., proANF 31–67) and amino acids 99–126 (i.e., ANF) after right ventricular pacing at 100, 125, 150, and 180 bpm in six male mongrel dogs. Right atrial and femoral vein blood was obtained at baseline, and at 5, 12, 19, 26, 56, 86, 116, 146, and 206 minutes after right ventricular pacing. Resulting plasma concentration‐time data derived parameters were compared. The disappearance rate constants for atrial and femoral venous proANF 1–98 were 0.0144 ± 0.0087 (X ± SD) and 0.0175 ± 0.0075 min−1, respectively (t = 0.6158) and release rate constants were 0.1569 ± 0.1504 and 0.0670 ± 0.0393 min−1, respectively (t = 1.8269; P > .05). The proANF 31–67 disappearance rate constants were 0.0139 ± 0.0082 and 0.0148 ± 0.0132 min−1, respectively (t = 0.1192) and release rate constants were 0.0957 ± 0.0414 and 0.1984 ± 0.1762 min−1, respectively (t = 1.4812). The ANF elimination phase disappearance rate constants were 0.0663 ± 0.0273 and 0.1116 ± 0.0539 min−1 (t = 2.0923, P > .05), respectively, and the release rate constants were 0.1335 ± 0.0532 and 0.1638 ± 0.0520 min−1 (t = 0.7878, P > .05), respectively. These data indicate that proANF 1–98 and proANF 31–67 circulating β post‐distribution half‐lives are approximately 45 minutes whereas β half‐life of ANF is 10 minutes. Persisting concentrations of proANF 1–98 and proANF 31–67 in plasma may better explain the proported sustained pharmacologic effects that have been attributed to ANF, which has a mean a distribution phase half‐life of 3.5 minutes and a β half‐life of 10 minutes.

CHANGE IN PLASMA IMMUNOREACTIVE N-TERMINUS, C-TERMINUS, AND 4,000-DALTON MIDPORTION OF ATRIAL NATRIURETIC FACTOR PROHORMONE WITH HEMODIALYSIS

Plasma concentrations of the immunoreactive N-terminus, C-terminus and 4,000-dalton midportion of the N-terminus of the atrial natriuretic factor (ANF) prohormone were measured before and after hemodialysis in 13 patients with end-stage renal disease. There was a significant (p less than 0.001) fall in the mean plasma concentration of the C-terminus (i.e. ANF, amino acids 99-126 of the prohormone) from 123 +/- 25 to 80 +/- 22 fmol/ml (mean +/- SEM) with dialysis. The whole N-terminus, on the other hand, increased from 9,336 +/- 2,011 to 11,021 +/- 2,134 fmol/ml after dialysis (p less than 0.002). Pro ANF 31-67 (i.e. amino acids 31-67 of the prohormone) increased postdialysis from 27,775 +/- 4,300 to 31,040 +/- 4,840 fmol/ml (p less than 0.003). Only 1.5% of pro ANF 1-98 and pro ANF 31-67 were cleared by the dialyzer membrane while 15% of ANF crossed the membrane. Thus, with hemodialysis the C-terminus decreases while the N-terminus and pro ANF 31-67 from the midportion of the N-terminus of the ANF prohormone increase in plasma which is partially explained by their respective abilities to cross the dialyzer membrane.

Plasma Prohormone Atrial Natriuretic Peptides 1-98 and 31-67 Increase with Supraventricular and Ventricular Arrhythmias

Recently two peptides consisting of amino acids (AA) 1-30 and 31-67 of the N-terminus of the 126 AA prohormone of atrial natriuretic factor (pro ANF) as well as atrial natriuretic factor (ANF, AA 99-126; C-terminus) were found to have vasodilatory and natriuretic properties. These peptides as well as ANF circulate in man as part of the N-terminus of the prohormone. To determine if the polyuria, associated with both ventricular and supraventricular arrhythmias, is associated with increased circulating concentrations of the N-terminus and C-terminus of the ANF prohormone, 20 individuals with spontaneous arrhythmias, including ten persons with atrial fibrillation, six with paroxysmal supraventricular tachycardia, and four with ventricular tachycardia, were evaluated before and after conversion to sinus rhythm. In all 20 patients, the circulating concentrations of the whole N-terminus (ie, AA 1-98), the midportion of the N-terminus (pro ANF 31-67) that circulates as a distinct 3900 molecular weight peptide after being proteolytically cleaved from the N-terminus, and the C-terminus were significantly higher (p less than 0.001) than their concentration in 54 persons with sinus rhythm. With conversion to sinus rhythm, the plasma C-terminus concentration of these 20 arrhythmia patients decreased to the level of persons with sinus rhythm within 30 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise increases the circulating concentration of the N-terminus of the atrial natriuretic factor prohormone in normal individuals☆

Recently two peptides consisting of amino acids (aa) 1 to 30 and 31 to 67 of the N-terminus of the 126 aa prohormone of atrial natriuretic factor (proANF), as well as atrial natriuretic factor (ANF, aa 99 to 126; C-terminus), were found to have vasodilatory and natriuretic properties. These peptides, as well as ANF, circulate in humans as part of the N-terminus of the prohormone. To determine the effect of graded exercise on the circulating concentrations of the N-terminus and C-terminus of the ANF prohormone in normal persons, 12 healthy individuals (mean age 45 +/- 2 years) were evaluated before, for 2 hours after, and during bicycle exercise at a work loads of 25, 50, 75, 100, 125, 150, and 175 W. Both the N- and C-terminus of the ANF prohormone were released simultaneously with graded exercise in direct proportion to the intensity of the work load, measured objectively via maximal oxygen consumption (VO2max), respiratory quotient, and heart rate. Both the N-terminus and C-terminus of the ANF prohormone had strong positive correlations (p less than 0.001) with blood pressure, heart rate, VO2max, and respiratory quotient. Following exercise, the C-terminus returned to preexercise levels within 30 minutes, while the N-terminus remained significantly elevated at 30 and 60 minutes postexercise, reflecting the longer half-life of the N-terminus in the circulation.