The effect of angiotensin II and ADH on the secretion of atrial natriuretic factor

Studies in intact animals have suggested that angiotensin II (AII) and antidiuretic hormone (ADH) increase the plasma concentration of atrial natriuretic factor (ANF). The purpose of these studies was to examine the effects of AII and ADH on ANF secretion in a rat heart-lung preparation under conditions where aortic pressure could be regulated and other indirect effects of these hormones eliminated. ANF secretion was estimated as the total amount of ANF present in a perfusion reservoir at the end of each 30-min period. A pump was used to deliver a fluorocarbon perfusate to the right atrium at rates of either 2 or 5 ml/min. In a time control series where venous return was maintained at 2 ml/min for three 30-min periods ANF secretion was 672 +/- 114, 794 +/- 91, and 793 +/- 125 pg/min (n = 6, P greater than 0.05). When venous return was increased from 2 to 5 ml/min ANF secretion increased from 669 +/- 81 to 1089 +/- 127 pg/min (P less than 0.01). The addition of AII to the perfusate in concentrations of 50, 100, or 200 pg/ml (n = 6 in each group) had no significant effect on basal ANF secretion or the ANF response to increasing venous return. Similarly, the addition of ADH to the perfusate in concentrations of 5, 25, or 100 pg/ml had no significant effect on ANF release from the heart. These results suggest that the ability of AII and ADH to increase plasma ANF concentration in vivo may be due to the effects of these hormones on right or left atrial pressure.     

Role of endothelin receptor subtypes in volume-stimulated ANF secretion

The role of endothelin (ET) receptors was tested in volume-stimulated atrial natriuretic factor (ANF) secretion in conscious rats. Mean ANF responses to slow infusions (3 x 3.3 ml/8 min) were dose dependently reduced (P < 0.05) by bosentan (nonselective ET-receptor antagonist) from 64.1 +/- 18.1 (SE) pg/ml (control) to 52.6 +/- 16.1 (0.033 mg bosentan/rat), 16.1 +/- 7.6 (0. 33 mg/rat), and 11.6 +/- 6.5 pg/ml (3.3 mg/rat). The ET-A-receptor antagonist BQ-123 (1 mg/rat) had no effect relative to DMSO controls, whereas the putative ET-B antagonist IRL-1038 (0.1 mg/rat) abolished the response. In a second protocol, BQ-123 (>/=0.5 mg/rat) nonsignificantly reduced the peak ANF response (106.1 +/- 23.0 pg/ml) to 74.0 +/- 20.5 pg/ml for slow infusions (3.5 ml/8.5 min) but reduced the peak response (425.3 +/- 58.1 pg/ml) for fast infusions (6.6 ml/1 min) by 49.9% (P < 0.001) and for 340 pmoles ET-1 (328.8 +/- 69.5 pg/ml) by 83.5% (P < 0.0001). BQ-123 abolished the ET-1-induced increase in arterial pressure (21.8 +/- 5.2 mmHg at 1 min). Changes in central venous pressure were similar for DMSO and BQ-123 (slow: 0.91 and 1.14 mmHg; fast: 4.50 and 4.13 mmHg). The results suggest 1) ET-B receptors mainly mediate the ANF secretion to slow volume expansions of <1.6%/min; and 2) ET-A receptors mainly mediate the ANF response to acute volume overloads.     

Specific binding of atrial natriuretic factor to renal glomeruli during day or night antiorthostatic suspension in the rat

We observed a significant increase in plasma atrial natriuretic factor (ANF) in antiorthostatic hypokinetic suspension (AOH) rats after 2 h of suspension when the experiment was made during day. Plasma ANF was investigated in relation to renal glomerular ANF receptors during AOH at night. The aim of this study was 1) to compare the day and night ANF responses to AOH 2) to determine whether the renal glomerular ANF receptors are involved. The rats were divided into 2 groups: i) 24 population cage (PC), and ii) 24 were attached by the tail (Morey's model) and remained in the horizontal position (attached horizontal-AH). Six AH were suspended (30 degrees) for 2 hours (AOH) and sacrificed with the controls: PC and AH (12.00h). The same experiment was made during the night (24.00h). A significant increase in plasma ANF was found in both AOH and AH after 2 h of suspension during day and night (19 +/- 2.3 pg/ml vs 9 +/- 0.95 and 18 +/- 3 pg/ml vs 10.2 +/- 1.8 respectively). PC rats had a significantly higher ANF level (38 +/- 5 pg/ml) than AH or AOH. The glomerular ANF receptor population was slightly lower in AOH than in AH (429 +/- 12 fmol/mg protein vs 507 +/- 5) during day. During night, a significantly lower number of ANF receptors was observed in AOH animals as compared to AH (168 +/- 2 fmol/mg protein vs 455 +/- 3). A decrease in glomerular receptors was also noted in PC during night. Day-time head-down tilt, bed rest or head-out water induced a natriuretic and diuretic response, whereas the normal recumbency at night does not lead to such effects. We conclude that the natriuretic and diuretic response not observed during night was associated with elevated plasma ANF levels and decreased ANF receptor density.     

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.     

Plasma immunoreactive atrial natriuretic factor (IR-ANF) increases markedly after alpha 2-adrenergic stimulation with clonidine in normally-hydrated rats

Clonidine, an alpha 2-adrenergic agonist, induced a marked, dose-related increase of plasma IR-ANF in normally-hydrated rats. Maximal ANF release was observed at 10 min after injection of 50 micrograms clonidine, rising from 40.5 +/- 4.6 pg/ml (X +/- SEM) to 1064.4 +/- 22.4 pg/ml. This effect on plasma IR-ANF was partially blocked by pretreatment with 0.8 mg naloxone, whereas synthetic Arg8-vasopressin (AVP) did not inhibit clonidine's action. These findings indicate that increased ANF release may be involved in the mechanism of clonidine-induced diuresis. The clonidine's effect on ANF release may be mediated via activation of opioid receptors besides stimulation of alpha 2-adrenergic receptors.     

Alterations in atrial and plasma atrial natriuretic factor (ANF) content during development of hypoxia-induced pulmonary hypertension in the rat

Distension of the atrial wall has been proposed as a signal for the increased release of atrial natriuretic factor (ANF) from atrial myocytes in response to perceived volume overload. To determine whether pressure changes resulting from hypertension in the pulmonary circulation may stimulate release of ANF, rats were exposed to chronic hypobaric hypoxia for 3 or 21 days and the ANF concentration in the atria and plasma were determined by specific radioimmunoassay. Exposure to chronic hypoxia resulted in significant increases in hematocrit at both 3 (p less than 0.025) and 21 days (p less than 0.005) and in the development of right ventricular hypertrophy (RVH) expressed as the ratio of the weight of the right ventricle to the weight of the left ventricle and septum (RV/LV+S) at both 3 (RV/LV+S = 0.278 +/- 0.005) and 21 days (RV/LV+S = 0.536 +/- 0.021). After 21 days, left atrial (LA) ANF content was significantly increased in hypoxic rats compared to controls (508 +/- 70 ng/mg tissue vs 302 +/- 37 ng/mg), while right atrial (RA) ANF content was significantly reduced (440 +/- 45 vs 601 +/- 58 ng/mg). At this time, plasma ANF concentration was significantly elevated compared to controls (238 +/- 107 pg/ml vs 101 +/- 10 pg/ml). These results suggest that the development of pulmonary hypertension following chronic hypobaric exposure induces altered atrial ANF content and increased plasma ANF concentration as a result of altered distension of the atrial wall.     

Plasma levels of atrial natriuretic factor in nonhibernating and hibernating marmots

Plasma atrial natriuretic factor (ANF) was measured in 16 marmots at various times of the year. Nonhibernating males (n = 6) had an average plasma concentration of 56 +/- 8 pg/ml; nonhibernating females (n = 6) had an average plasma concentration of 61 +/- 4 pg/ml. During hibernation an additional group of females (n = 4) showed an average of 25 +/- 5 pg/ml. Plasma ANF of both groups of nonhibernating marmots was significantly higher (P less than 0.01) than that the hibernating group, but there was no difference between nonhibernating males and females.     

Behavior of atrial natriuretic factor in an experimental model of Trypanosoma cruzi infection in rats

Enhanced atrial natriuretic factor (ANF) production by the heart is related to hemodynamic overload, cardiac growth, and hypertrophy. The heart is one of the most affected organs during Trypanosoma cruzi infection. We tested the hypothesis that myocarditis produced by parasite infection alters the natriuretic peptide system by investigating the behavior of plasma ANF during the acute and chronic stages of T. cruzi infection in rats. Sprague-Dawley rats were infected with T. cruzi clone Sylvio-X10/7. Cardiac morphology showed damage to myocardial cells and lymphocyte infiltration in the acute phase; and fibrosis and cell atrophy in the chronic period. Plasma ANF levels (radioimmunoassay) were significantly higher in acute (348 +/- 40 vs. 195 +/- 36 pg/ml, P < 0.05, n = 17) and chronic T. cruzi myocarditis (545 +/- 81 vs. 229 +/- 38 pg/ml, P < 0.001, n = 11) than in their respective controls (n = 10 and 14). Rats in the chronic phase also showed higher levels than rats in the acute phase (P < 0.01). The damage of myocardial cells produced by the parasite and the subsequent inflammatory response could be responsible for the elevation of plasma ANF during the acute period of T. cruzi infection. The highest plasma ANF levels found in chronically infected rats could be derived from the progressive failure of cardiac function.     

Cortisol effect on atrial natriuretic factor response to hypertonic saline in fetal sheep.

Atrial natriuretic factor (ANF) is released following a variety of stimuli including hypertonicity in the fetus. To study the effect that cortisol has on fetal ANF release, seven chronically instrumented fetal sheep at gestational ages ranging from 110-132 days were studied in two experiments. In one experiment (CORTISOL), a continuous cortisol (with EtOH vehicle) infusion was maintained. In the other experiment (CONTROL), the vehicle was infused alone. Ninety minutes from the start of this infusion, a hypertonic saline bolus (12 meg/kg) was given. Osmolality, ANF, cortisol, pH, PO2, PCO2, mean arterial pressure (MAP), heart rate (HR), and hematocrit (HCT) were followed over a 120-min period. Following hypertonic saline, serum osmolality increased from 290.6 +/- 2.3 mOsm/kg to 310.4 +/- 2.5 mOsm/kg (P < 0.01). Baseline values for pH, PO2, and HCT were 7.37 +/- 0.01, 22.5 +/- 1.6 mmHg, and 33.9 +/- 1.2 respectively. Each of these variables fell following hypertonic saline infusion. MAP rose from 40.6 +/- 1.7 mmHg to 47.0 +/- 2.4 mmHg (P < 0.01). However, there were no differences between CONTROL and CORTISOL experiments in any of the above changes. Cortisol levels in the CONTROL group did not change during the course of the experiment, but in the CORTISOL group rose from 8.2 +/- 4.4 ng/ml to 33.0 +/- 9.9 ng/ml (P = 0.02). Plasma ANF levels prior to hypertonic saline were similar (124.8 +/- 17.7 pg/ml and 127.6 +/- 26.1 pg/ml) in the CONTROL and CORTISOL groups respectively and rose following hypertonic saline to a maximum of 155.3 +/- 16.6 pg/ml and 189.2 +/- 42.7 pg/ml (P = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Atrial natriuretic factor in human plasma

A reproducible and sensitive radioimmunoassay (RIA) was developed to measure ANF in human plasma. Immunoreactive ANF was extracted from plasma with Sep-Pak cartridges, using 0.2% ammonium acetate (pH 4) with acetonitrile. The sensitivity of the assay was 3.9 pg/ml. The coefficient of variance for inter-assay and intra-assay was 16.8% and 6.8%, respectively. In normal healthy subjects (n = 67), ANF content was 11.9 +/- 1.3 pg/ml (mean +/- SEM). Significantly-higher ANF concentrations were found in proximal coronary sinus blood, being 6 to 37 times greater than in the peripheral circulation. Comparison of the prior extraction method with direct RIA revealed a good correlation (r = 91) in samples containing higher than 100 pg/ml ANF. No correlation was observed with lower values. The elution profiles of reverse-phase HPLC of peripheral and coronary sinus plasma extracts were similar but somewhat complex, with the main immunoreactive peak corresponding to a low-molecular-weight peptide.     

Atrial natriuretic factor inhibits the CRH-stimulated secretion of ACTH and cortisol in man.

Corticotrophic secretion of ACTH is stimulated by corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP), and suppressed by glucocorticoids. In vitro and preclinical studies suggest that atrial natriuretic factor (ANF) may be a peptidergic inhibitor of pituitary-adrenocortical activity. The aim of this study was to elucidate a possible role of ANF as a modulator of ACTH release in humans. A bolus injection of 100 micrograms human CRH (hCRH) during a 30 min intravenous infusion of 5 micrograms/min human alpha atrial natriuretic factor (h alpha ANF) was administered at 19:00 to six healthy male volunteers. In comparison to saline, a blunted CRH-stimulated secretion of ACTH (mean maximum plasma level +/- SD 45 min after hCRH: saline 46.2 +/- 14.2 pg/ml, h alpha ANF 34.6 +/- 13.8 pg/ml, p-value = 0.007) and a delayed rise (10 min) in cortisol were detected. The maximum plasma cortisol levels remained nearly unchanged between saline and h alpha ANF administration (mean maximum plasma level +/- SD 60 min after hCRH: saline 182 +/- 26 ng/ml, h alpha ANF 166 +/- 54 ng/ml). No effects of h alpha ANF on basal cortisol levels were observed; in contrast, basal ACTH plasma levels were slightly reduced. Basal blood pressure and heart rate remained unaffected. In the control experiment, infusion of 3 IU AVP in the same experimental paradigm increased basal and stimulated ACTH and cortisol levels significantly in comparison to saline. These observations suggest that intravenously administered haANF inhibits the CRH-stimulated release of ACTH in man.     

Atrial natriuretic factor and renal sodium excretion during ventilation with PEEP in hypervolemic dogs.

Controlled mandatory ventilation with positive end-expiratory pressure (PEEP) reduces renal sodium excretion. To examine whether atrial natriuretic factor (ANF) is involved in the renal response to alterations in end-expiratory pressure in hypervolemic dogs, experiments were performed on anesthetized dogs with increased blood volume. Changing from PEEP to zero end-expiratory pressure (ZEEP) increased sodium excretion by 145 +/- 61 from 310 +/- 61 mumol/min and increased plasma immunoreactive (ir) ANF by 104 +/- 27 from 136 +/- 21 pg/ml. Changing from ZEEP to PEEP reduced sodium excretion by 136 +/- 36 mumol/min and reduced plasma irANF by 98 +/- 22 pg/ml. To examine a possible causal relationship, ANF (6 ng.min-1.kg body wt-1) was infused intravenously during PEEP to raise plasma irANF to the same level as during ZEEP. Sodium excretion increased by 80 +/- 36 from 290 +/- 78 mumol/min as plasma irANF increased by 96 +/- 28 from 148 +/- 28 pg/ml. We conclude that alterations in end-expiratory pressure lead to great changes in plasma irANF and sodium excretion in dogs with increased blood volume. Comparison of the effects of altering end-expiratory pressure and infusing ANF indicates that a substantial part of the changes in sodium excretion during variations in end-expiratory pressure can be attributed to changes in plasma irANF.     

Hormonal interactions and renal function during mechanical ventilation and ANF infusion in humans

To investigate the influence of atrial natriuretic factor (ANF) on renal function during mechanical ventilation (MV), we examined the renal and hormonal responses to synthetic human ANF infusion in eight patients during MV with zero (ZEEP) or 10 cmH2O positive end-expiratory pressure (PEEP). Compared with ZEEP, MV with PEEP was associated with a reduction in diuresis (V) from 208 +/- 51 to 68 +/- 11 ml/h (P less than 0.02), in natriuresis (UNa) from 12.4 +/- 3.3 to 6.2 +/- 2.1 mmol/h (P less than 0.02), and in fractional excretion of sodium (FENa) from 1.07 +/- 0.02), 0.21 to 0.67 +/- 0.17% (P less than 0.02) and with an increase in plasma renin activity (PRA) from 4.83 +/- 1.53 to 7.85 +/- 3.02 ng.ml-1.h-1 (P less than 0.05). Plasma ANF levels markedly decreased during PEEP in four patients but showed only minor changes in the other four patients, and mean plasma ANF levels did not change (163 +/- 33 pg/ml during ZEEP and 126 +/- 30 pg/ml during PEEP). Glomerular filtration rate and renal plasma flow were unchanged. Infusion of ANF (5 ng.kg-1.min-1) during PEEP markedly increased V and UNa by 110 +/- 61 and 107 +/- 26%, respectively, whereas PRA decreased from 7.85 +/- 3.02 to 4.40 +/- 1.5 ng.ml-1.min-1 (P less than 0.05). In response to a 10 ng.kg-1.min-1 ANF infusion, V increased to 338 +/- 79 ml/h during ZEEP but only to 134 +/- 45 ml/h during PEEP (P less than 0.02), whereas UNa increased, respectively, to 23.8 +/- 5.3 and 11.3 +/- 3.3 mmol/h (P less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)     

Atrial natriuretic factor in essential hypertension

We measured circulating levels of immunoreactive atrial natriuretic factor (ANF) in 10 patients with untreated, uncomplicated mild to moderate essential hypertension and in 15 normotensive controls. ANF concentrations were significantly higher in the hypertensive group than in the control group (38.4 +/- 6.9 pg/ml versus 18.3 +/- 1.8 pg/ml, p less than 0.02). A positive correlation between ANF levels and systolic, diastolic and mean blood pressure was noted in the total study population (p less than 0.008, r = 0.52; p less than 0.005, r = 0.55; p less than 0.02, r = 0.46, respectively). Thus, plasma ANF concentrations are elevated in essential hypertension and may result from increased intraarterial pressure.     

Atrial natriuretic factor-like peptide and its prohormone within single cell organisms.

The present investigation was designed to determine if the atrial natriuretic peptide hormonal system is present within single cell organisms. Paramecium multimicronucleatum were examined with 3 sensitive and specific radioimmunoassays which recognize the N-terminus [amino acids 1-98; proANF(1-98)], the midportion of the N-terminus [amino acids 31-67; proANF(31-67)] and C-terminus (amino acids 99-126; ANF) of the 126 amino acid atrial natriuretic factor (ANF) prohormone. ProANF(1-98), proANF(31-67), and ANF-like peptides were all present within these unicellular organisms at concentrations of 460 +/- 19 pg/ml, 420 +/- 15 pg/ml, and 14.5 +/- 2 pg/ml, respectively. These concentrations are similar to their respective concentrations in the plasma of the rat (Rattus norvegicus). These results suggest that even single cell organisms contain the atrial natriuretic peptide-like hormonal system.     

Effect of different anesthetics on immunoreactive atrial natriuretic factor concentrations in rat plasma

The effect of different conditions of blood withdrawal and use of different anesthetics on immunoreactive atrial natriuretic factor (IR-ANF) concentrations in plasma was studied in rats. The concentration of IR-ANF in plasma from jugular vein of non-anesthetized conscious rats, cannulated either 24 hr before blood withdrawal was 93.9 +/- 17.1 pg/ml (n = 30); and 48 hr: 81.9 +/- 11.5 pg/ml (n = 29). Immobilization stress (4 hr) increased IR-ANF concentration: 248.0 +/- 80.2 pg/ml (n = 5). Anesthesia by morphine, diethyl-ether, chloral hydrate and ketamine chlorhydrate increased IR-ANF concentrations to 2,443.0 +/- 281.2 pg/ml (n = 24), 806.1 +/- 74.6 pg/ml (n = 64), 224.0 +/- 81.4 pg/ml (n = 20), and 195.0 +/- 20.3 pg/ml (n = 51), respectively. IR-ANF in plasma of sodium-pentobarbital and urethane anesthetized rats was 59.2 +/- 6.7 pg/ml (n = 10) and 42.6 +/- 8.1 pg/ml (n = 8), respectively. These changes in IR-ANF evoked by different types of anesthetics and different conditions of blood withdrawal have to be taken into consideration during studies on the physiopathological role of atrial natriuretic factor.     

Effect of chronic infusion of synthetic atrial natriuretic factor (ANF 8-33) in conscious two-kidney, one-clip hypertensive rats

Conscious two-kidney, one-clip hypertensive rats were chronically infused during 7 days with synthetic ANF (8-33) (1 microgram/hr/rat) by means of osmotic minipumps. The initial blood pressure of 183 +/- 4 mmHg gradually decreased to 116 +/- 5 mmHg the last 2 days of infusion. Pressure diuresis returned to normal and pressure natriuresis was attenuated. PRA was significantly lower (1.81 +/- 0.41 AI ng/ml/hr) than in not treated hypertensive rats (8.56 +/- 3.75 AI ng/ml/hr). A partial regression in cardiac hypertrophy was observed in the treated group. We suggest that the hypotensive response to ANF may be mainly due to vasodilatation, but the possibility that the decrease in PRA may play a partial role in lowering blood pressure, cannot be excluded.     

The responses of atrial natriuretic factor concentrations to acute volume changes in conscious rats

A rapid and sensitive radioimmunoassay has been developed for measurements of atrial natriuretic factor (ANF) in rat plasma. The antiserum, raised to rat ANF (99-126), cross-reacts with rat ANF (103-123), ANF (103-125), ANF (103-126) but not with smaller fragments, human ANF (99-126), angiotensin II, bradykinin or vasopressin. The plasma ANF concentration is 181 +/- 24 pg/ml (N = 24) in the unstressed conscious rats (Charles River CD, male). The ANF immunoreactivity in the plasma extracts was verified by HPLC analysis, which displayed one major immunoreactive peak of ANF corresponding to rat ANF (99-126) and some smaller fragments. Intravenous injection of saline elevated circulating ANF, whereas acute volume depletion by hemorrhage, water deprivation and furosemide diuresis greatly lowered plasma ANF. The prompt response of plasma ANF levels to acute changes in volume status is consistent with the proposed role of ANF as a volume-regulatory hormone.     

Immunoreactive atrial natriuretic factor (IR-ANF) in human plasma

A direct radioimmunoassay for ANF in human plasma was developed. A synthetic alpha-human atrial peptide (Ser 99-Tyr 126) was used for preparation of the iodinated tracer and the standards. The sensitivity of the method is 1.9 pg/ml. Concentration of immunoreactive ANF (IR-ANF) in plasma of 59 clinically normal subjects was 65.3 +/- 2.5 pg/ml (mean +/- SE). In two patients who underwent atrial pacing an increase of about 100 percent in circulating IR-ANF was observed. IR-ANF was extracted from human plasma by Vycor glass and purified by HPLC. The main immunoreactive isolated peak contained a low molecular weight peptide.     

The effect of atrial natriuretic peptide on small intestinal contractility and transit.

Isometric tension in response to ANF (10(-10) to 10(-4) M) was recorded from longitudinally and circularly oriented rat jejunal smooth muscle strips. Conscious, fasted rats received an IV infusion of 1.25 nmol ANF/100 g body weight in 0.5 ml normal saline and controls received saline alone. Five minutes later 10 muCi Na2 51CrO4 in 0.5 ml saline was instilled through a jejunostomy. Fifteen minutes later animals were sacrificed, and the gut divided into 8 equal segments of small intestine, cecum and remaining colon. The radioactivity of each segment was measured and a geometric center of transit determined for each group. ANF induced relaxation of longitudinally oriented strips (Tm = -72.3 +/- 10.7 mN/g, ED50 7.3 +/- 3.6 x 10(-8) M), and contraction of circularly oriented strips (Tm = 35.0 +/- 5.0 mN/g, ED50 1.3 +/- 1.0 x 10(-8) M). This response was unaffected by 10(-6) M tetrodotoxin. The geometric mean center of transit was significantly (p less than 0.001) further aboral in ANF-treated compared to control animals (intestinal segment 4.2 +/- 0.2 vs. 3.2 +/- 0.2).