Inder R. Sarda

Secretion of atrial natriuretic peptide and vasopressin by small cell lung cancer

Background. Hyponatremia in patients with small cell lung cancer (SCLC) is a common clinical problem usually attributed to tumor secretion of arginine vasopressin (AVP). It recently was shown that some SCLC cell lines produce atrial natriuretic peptide (ANP). The purpose of this investigation was to determine the frequency and clinical consequences of secretion of ANP by SCLC and the relative contribution of ANP and AVP to the hyponatremia associated with this disease.

Isolation and characterization of iso-rANP, a new natriuretic peptide from rat atria

Using a specific radioimmunoassay we have isolated and sequenced a new 45-amino acid peptide from rat atria which exhibits similar physiological and pharmacological properties to rat atrial natriuretic peptide (rANP). We have termed the new peptide iso-rANP, because of its functional and structural similarities to rANP. Amino acid sequence differences show that iso-rANP is genetically distinct from rANP. Iso-rANP has a single disulfide bond between residues 23-39 and this portion of the peptide shows substantial homology to rANP and to porcine brain natriuretic peptide (BNP). Little homology is evident at the N- and C-termini of iso-rANP and ANP. Iso-rANP is equipotent with rANP in eliciting diuresis, natriuresis and hypotension in the bioassay rat.

Hormonal studies in pregnancy

The concentration of unconjugated total estrogens (primarily estrone, estradiol-17beta, and estriol) were measured by rapid radioimmunoassay method in serum samples from maternal peripheral vein, cord vein, and cord artery in normal pregnancies at delivery. The serum concentration of total free estrogens found in cord vein was four to five times higher than in maternal peripheral vein and cord artery. Levels obtained in maternal peripheral vein, cord vein, and cord artery were 47.8+/-1.8, 140.1+/-8.57, 31.8+/-2.15 ng. per millilitre (+/-standard error of the mean), respectively. These values are compared with those reported by others.

Expression of B-type natriuretic peptide in atrial natriuretic peptide gene disrupted mice.

Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) are two hormones produced and secreted by the heart to control blood pressure, body fluid homeostasis and electrolyte balance. Each peptide binds to a common family of 3 receptors (GC-A, GC-B and C-receptor) with varying degrees of affinity. The proANP gene disrupted mouse model provides an excellent opportunity to examine the regulation and expression of BNP in the absence of ANP. A new radioimmunoassay (RIA) was developed in order to measure mouse BNP peptide levels in the plasma, atrium and ventricle of the mouse. A detection limit of 3–6 pg/tube was achieved by this assay. Results show that plasma and ventricular level of BNP were unchanged among the three genotypes of mice. However, a significant decrease in the BNP level was noted in the atrium. The homozygous mutant (ANP–/–) had undetectable levels of BNP in the atrium, while the heterozygous (ANP+/–) and wild-type (ANP+/+) mice had 430 and 910 pg/mg in the atrium, respectively. Northern Blot analysis shows the ANP–/– mice has a 40% reduction of BNP mRNA level in the atrium and a 5-fold increase in the ventricle as compared with that of the ANP+/+ mouse. Our data suggest that there is a compensatory response of BNP expression to proANP gene disruption. Despite the changes in the atrial and ventricular tissue mRNA and peptide levels, the plasma BNP level remains unaltered in the ANP–/– mice. We conclude that the inability of BNP to completely compensate for the lack of ANP eventually leads to chronic hypertension in the proANP gene disrupted mice.

Acute ethanol ingestion modifies the circulating plasma levels of atrial natriuretic peptide

Since ethanol ingestion is associated with a disruption of water and electrolyte balance in a variety of species, we sought to evaluate the regulatory control of atrial natriuretic peptide (ANP) in response to acute doses of ethanol. Male Sprague-Dawley rats were administered a 5-g/kg dose of ethanol (40% w/v) via a gastric tube, while control animals received an equivalent volume of water. Expressed as a percentage of control, plasma ANP levels were 39.0%, 28.5%, and 23.6% in the ethanol-treated animals at 30, 60, and 120 min postintubation, respectively. Ethanol-treated animals displayed blood alcohol concentrations of 89.0, 137.6, and 214.1 mg/dl at the same time periods. After 120 min, plasma renin activity was elevated from 8.7 to 20.3 ng/ml/h in conjunction with an increase in the levels of circulating aldosterone from 16.3 to 42.5 ng/dl and an increase in plasma vasopressin from 2.2 to 3.6 pg/ml. Levels of atrial ANP mRNA remained consistent over the time course of the experiment, and no changes in the amount of ventricular ANP transcript were observed. Tissue ANP levels were similar between ethanol-treated and water-loaded control animals. In vitro experiments using cultured cardiac myocytes suggest that ethanol exposure may not directly affect ANP secretion. We propose that acute ethanol treatment may inhibit atrial distension and subsequently modify the control of ANP release under volume loading conditions.

Heterotopic columnar epithelium and adenosis in the vagina of the mouse after neonatal treatment with clomiphene citrate

Physiologically, the epithelium of the mouse vagina undergoes conversion during early postnatal life from columnar to stratified squamous. A similar process in the human occurs in the late first and early second trimesters of pregnancy. The mouse vagina has been identified as a good developmental model of the human. Previous work in the mouse has shown that this process is affected by neonatal administration of diethylstilbestrol. We have administered diethylstilbestrol and clomiphene citrate to parallel groups of BALB/c neonatal mice. They were followed up to 24 weeks. In both groups, persistent columnar or heterotopic columnar epithelium, not seen in the control mice, was identified and associated with adenosis. This effect of diethylstilbestrol and clomiphene citrate appears to be similar to the biologic response to transplacental diethylstilbestrol in the human. After transplacental diethylstilbestrol, malignant vaginal tumors rarely develop. If clomiphene citrate, given to the human prior to pregnancy to induce ovulation or by inadvertence during pregnancy, were to circulate into the critical time of vaginal differentiation, a similar biologic potential may exist. The first situation seems to be unlikely. The second is of more concern.

Immunoactive iso-ANP/BNP in plasma, tissues and atrial granules of the rat

We have developed a specific radioimmunoassay (RIA) for iso-rANP(1-45)/rBNP(51-95) using antiserum produced against a peptide comprise of the first 20 amino acid sequence of this cardiac hormone. Using this RIA, we found that atria contained the highest amount of iso-rANP(1-45) (567.37 pmol/g) which is about 140-fold higher than ventricles (4.32 pmol/g). With the exception of the lung and kidney, all other tissues had negligible amounts. The plasma level was 1.4 fmol/ml and the only molecular form found was the 45 amino acid form. HPLC analysis of extracts of isolated, purified atrial granules revealed that, like atrial natriuretic peptide (ANP), iso-rANP/rBNP is also stored in these granules. However, while ANP is stored predominantly as pro-ANP(1-126) and cleaved during or after release, iso-ANP/BNP is stored as the 45 amino acid form and may be processed prior to storage in the granules.

Unconjugated serum oestriol levels in mother and baby with meconium staining of the amniotic fluid.

To examine the effect on oestrogen metabolism of the stimulus which causes the passage of meconium, we measured maternal venous and cord artery and vein serum unconjugated oestriol levels in 46 patients with meconium staining of the amniotic fluid and 19 controls. Mean cord vein oestriol levels were significantly lower than in controls in the presence of meconium stained amniotic fluid and no fetal acidosis (cord artery buffer base of 36·2 meq/l or more) (P<0·02). The same tendency was seen with acidotic infants (P

Hormonal studies in pregnancy: II. Unconjugated estriol in maternal peripheral vein, cord vein, and cord artery serum at delivery in pregnancies complicated by intrauterine growth retardation☆

The levels of unconjugated estriol in maternal vein serum during labor, cord artery serum, and cord vein serum were measured in normal pregnancy and in pregnancy complicated by intrauterine growth retardation. The mean level of unconjugated estriol in maternal vein serum was significantly lower in the intrauterine growth-retarded group than in the normals (p less than 0.001). The mean estriol level in cord vein was lower only in the most severely growth-retarded subgroup as compared to the normal. There was no difference seen in the cord artery values among the groups.

Radioimmunoassay for Rat B-Type Natriuretic Peptide (BNP-45)

Rat BNP-45 is the main circulating form of BNP in rat plasma. To understand the role of BNP in physiological and pathophysiological conditions, a specific radioimmunoassay (RIA) for the quantitative determination of the peptide in plasma and tissues is necessary. An assay using rBNP-45 as the standard in conjunction with antisera directed against this peptide has not been described in the literature, though some investigators have reported values ranging from 0.73-2.0 pmol/L using either BNP-26 or BNP-32 as the standard peptide. Unfortunately, these forms of BNP do not exist in rat plasma. In our studies, we have developed a specific RIA for rBNP-45 using rBNP-45 as the standard peptide and Tyro-rBNP-45 as the radioligand. We have used two specific antisera for assay purposes; one against rBNP-45, and the second to a peptide composed of the first 20 amino acids of rBNP-45 (rBNP[1-20]). The recovery of various amounts of rBNP-45 added to control plasma was 50-80% depending on the method of extraction and purification. The interassay and intraassay coefficients of variation were 12% and 6% respectively. Values obtained were similar for blood sampled by either cardiac puncture, decapitation, or aortic puncture. The method was used to measure rBNP-45 in the plasma of normal (WKY) and Spontaneously Hypertensive (SHR) rats. The values obtained were 5.46 +/- 0.43 and 19.6 +/- 2.36 pmol/L respectively. The rat atrial natriuretic peptide (ANP[99-126]) values in the same extracts were 23.2 +/- 0.45 and 51.6 +/- 3.16 pmol/L.