Adrenal cortex contributes to the regulation of NaCl-stimulated ANP release in the rat

Involvement of plasma atrial natriuretic peptide in protracted alcohol withdrawal

OBJECTIVE

Atrial natriuretic peptide (ANP) has been shown to inhibit the effects of corticotrophin releasing hormone, corticotrophin and cortisol, and to influence affective and anxiety symptoms in man. We tested the hypothesis of whether ANP is associated with endocrine and psychopathological disturbances during acute alcohol withdrawal.

METHOD

ANP and cortisol plasma concentrations were studied in alcoholics during in-patient detoxification and in healthy controls. Additionally, craving, depressive mood and anxiety were assessed.

RESULTS

Although mean ANP levels increased significantly in alcoholics between days 1 and 14, they remained diminished compared to controls. Separating a subgroup of alcoholics with a decrease of ANP levels during withdrawal, these individuals revealed significantly elevated scores for mean and maximum craving and a trend to an elevated self-rated anxiety on day 14.

CONCLUSION

We suggest that a dysregulation of ANP plasma levels during alcohol withdrawal may contribute to symptoms of protracted withdrawal such as craving and anxiety.

Mechanism of hyperosmolality stimulation of ANP secretion: its dependency on calcium and sodium

The calcium dependency of hyperosmolality stimulation of atrial natriuretic peptide (ANP) secretion was determined using isolated superfused nonbeating rat left atrium. Increasing osmolality by 65, 85, and 100 mosmol/kgH2O by superfusion with sucrose produced a peak rise in ANP secretion of 1.8-, 2.0-, and 2.7-fold. To determine whether calcium influx played a role in osmolality (osm)-stimulated ANP secretion, atria were superfused with 2 mM lanthanum, a calcium antagonist. Lanthanum inhibited by 85% the response to a 100 mosmol/kgH2O increase in osm. The voltage-dependent calcium channel blocker isradipine had no effect on osm-stimulated ANP secretion, suggesting that calcium influx via voltage-dependent calcium channels was not playing a significant role. Likewise, depleting sarcoplasmic reticulum calcium with 1 microM ryanodine did not block the response to osm, suggesting that calcium influx was not adequate to induce consequential release of calcium from the sarcoplasmic reticulum. To determine whether calcium influx was via Na(+)-Ca2+ exchange, we determined the sodium dependency of osm-stimulated ANP secretion. Replacement of sodium with lithium or choline blocked the secretory response to 100 mosmol/kgH2O. We conclude that osm-stimulated ANP secretion is calcium and sodium dependent. Calcium influx via Na(+)-Ca2+ exchange is highly implicated as the mechanism of cellular calcium entry.

The effects of methylprednisolone and the ganglioside GM1 on acute spinal cord injury in rats

Recent clinical trials have reported that methylprednisolone sodium succinate (MP) or the monosialic ganglioside GM1 improves neurological recovery in human spinal cord injury. Because GM1 may have additive or synergistic effects when used with MP, the authors compared MP, GM1, and MP+GM1 treatments in a graded rat spinal cord contusion model. Spinal cord injury was caused by dropping a rod weighing 10 gm from a height of 1.25, 2.5, or 5.0 cm onto the rat spinal cord at T-10, which had been exposed via laminectomy. The lesion volumes were quantified from spinal cord Na and K shifts at 24 hours after injury and the results were verified histologically in separate experiments. A single dose of MP (30 mg/kg), given 5 minutes after injury, reduced 24-hour spinal cord lesion volumes by 56% (p = 0.0052), 28% (p = 0.0065), and 13% (p > 0.05) in the three injury-severity groups, respectively, compared to similarly injured control groups treated with vehicle only. Methylprednisolone also prevented injury-induced hyponatremia and increased body weight loss in the spine-injured rats. When used alone, GM1 (10 to 30 mg/kg) had little or no effect on any measured variable compared to vehicle controls; when given concomitantly with MP, GM1 blocked the neuroprotective effects of MP. At a dose of 3 mg/kg, GM1 partially prevented MP-induced reductions in lesion volumes, while 10 to 30 mg/kg of GM1 completely blocked these effects of MP. The effects of MP on injury-induced hyponatremia and body weight loss were also blocked by GM1. Thus, GM1 antagonized both central and peripheral effects of MP in spine-injured rats. Until this interaction is clarified, the authors recommend that MP and GM1 not be used concomitantly to treat acute human spinal cord injury. Because GM1 modulates protein kinase activity, protein kinases inhibit lipocortins, and lipocortins mediate anti-inflammatory effects of glucocorticoids, it is proposed that the neuroprotective effects of MP are partially due to anti-inflammatory effects and that GM1 antagonizes the effects of MP by inhibiting lipocortin. Possible beneficial effects of GM1 reported in central nervous system injury may be related to the effects on neural recovery rather than acute injury processes.

Plasma ANP during hypertonic NaCl infusion in man

To determine the relationship between hyperosmolality and immunoreactive atrial natriuretic peptide of heart atrial plasma six healthy men were given 0.06 ml kg-1 min-1 855 mmol l-1 NaCl, i.v., for 2 h. The right atrial pressure and atrial plasma atrial natriuretic peptide were measured. During the infusion, right atrial pressure was kept constant by lowering the legs of the subject in a supine position downwards if any increase in the pressure was seen. There was a significant and linear increase in atrial serum osmolality, from 288 +/- 3.3 to 307 +/- 3.2 mOsm kg-1 (P less than 0.001). No statistically significant changes in right atrial pressure were seen. Regression analysis revealed that there was a statistically significant correlation between serum osmolality and plasma ANP in three subjects (responders) (r2: 0.5241, 0.8965, 0.6695). In three other subjects (nonresponders), there was no correlation between osmolality and ANP. The mean basal osmolality of responders was 280 mOsm kg-1 and the mean basal osmolality of nonresponders was 295 mOsm kg-1. In contrast, all subjects responded with an increase in plasma ANP (P less than 0.05) after RAP had been increased by tilting the legs of the subject upwards for 30 min. We conclude that the right atrial pressure regulates the release of atrial natriuretic peptide. Serum hyperosmolality may also contribute to the regulation of atrial natriuretic peptide independently of the right atrial pressure in man.

Plasma immunoreactive atrial natriuretic peptide and vasopressin after ethanol intake in man

To study the mechanisms of alcohol-induced diuresis, the plasma concentration of immunoreactive atrial natriuretic peptide and arginine vasopressin, serum sodium and osmolality, plasma renin activity and aldosterone, urinary sodium and volume, free water clearance, blood pressure and heart rate were measured in seven healthy men after oral intake of ethanol (1.5 g kg-1 in 6 h). Serum ethanol levels increased to 27 +/- 4 mmol l-1 (mean +/- SD) in 30 min and remained detectable for 14 h. Serum osmolality rose from 280 +/- 10 to 340 +/- 4 mosm kg-1 in 2 hours (P less than 0.01) and was 300 +/- 4 at 14 h (P less than 0.01). Formation of hypotonic urine began after the alcohol intake and resulted in a net loss of 0.9 +/- 0.1 kg water in 2 h. Free water clearance increased from -3.4 +/- 1.4 to 2.8 +/- 1.5 ml min-1 in 2 h (P less than 0.01). Plasma immunoreactive arginine vasopressin decreased from 5.7 +/- 2.1 to 3.3 +/- 1.3 ng l-1 (P = 0.05) in 30 min and increased to 17 +/- 25 and 12 +/- 10 ng l-1 at 6 and 12 h, respectively (P less than 0.05 for both). Plasma immunoreactive atrial natriuretic peptide levels decreased from 17 +/- 9 to the minimum of 11 +/- 3 ng l-1 in 2 h (P less than 0.01) and returned to the initial levels in 6 h. Serum sodium, plasma renin activity and plasma aldosterone increased maximally by 4 +/- 2, 165 +/- 153 and 143 +/- 101% (P less than 0.01 each) during 1-6 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Daily patterns of plasma atrial natriuretic peptide, serum osmolality and haematocrit in the rat

The present study documents daily rhythms of plasma atrial natriuretic peptide, serum osmolality and haematocrit in the rat. One-hundred and twenty-five Sprague-Dawley rats were used. They were bred under a cycle of 12 h light/12 h dark starting at 07.00 h. Fifty-three rats were decapitated between 09.00 and 16.00 h (study I) and 72 rats in groups of six were decapitated at 2-h intervals for a period of 24 h (study II). In study I, plasma atrial natriuretic peptide was 156 +/- 11 pg mg-1 (mean +/- SEM). In study II, atrial natriuretic peptide was at a control level from 08.00 to 18.00 h and then began to increase. At 22.00 h, atrial natriuretic peptide was 420 +/- 105 pg ml-1, which was significantly higher than at 08.00 h (P less than 0.05). The serum osmolality was over 300 mosmol kg-1 during the day. The highest mean osmolalities (315, 317, 312 mosmol kg-1) were found from 18.00 to 22.00 h. These were significantly different (P less than 0.05) from other groups during the day. The haematocrit was highest at 14.00 h (49.5 +/- 0.7%) and lowest at 24.00 h (43.6 +/- 0.8%) (P less than 0.05). In conclusion, we have shown that there are significant daily rhythms of plasma atrial natriuretic peptide, serum osmolality and haematocrit during a 24-h period and 12 h light/12 h dark cycle in the rat.