Urinary corticotropin-releasing hormone immunoreactivity is elevated during human pregnancy

Plasma corticotropin-releasing hormone immunoreactivity (CRH IR) rises with gestational age in women. In order to investigate the physiological changes of the hormone in pregnant women's urine, CRH IR was measured by radioimmunoassay in urine collected over a 24-hour period, a blood sample and a subsequent single collection of urine after the 24-hour collection (spot urine). Plasma CRH IR in pregnant subjects, 8682.8 ± 2063.0 pg CRH IR/ml plasma (mean ± SEM, n=25), was significantly higher than that in the non-pregnant controls (7.2 ± 1.6 pg/ml, n=5; separate t=4.21, p=0.0003, d.f.=24). Similarly, pregnant women had higher spot urine CRH IR - 54.6 ± 15.5 pg/μmol creatinine (Cr) versus 5.0 ± 0.5 pg/μmol Cr (separate t - 3.20, p=0.0038, d.f.=24.0) - and 24-hour urine CRH IR - 13.7 ± 1.2 pg/μmol Cr compared with 7.7 ± 0.8 pg/μmol Cr (separate t=4.28, p=0.003, d.f.=24.4) than the non-pregnant cohort. The difference between urinary excretion of CRH IR as estimated by 24-hour urine (13.7 ± 1.2 pg/(μmol Cr) and spot urine (54.6 ± 15.5 pg/μmol Cr) indicated that CRH IR in 24-hour urine may be degraded during storage. The weak associations between plasma and 24-hour urine CRH IR of pregnant women (correlation coefficient r=0.34, p > 0.1), and total 24-hour urine and spot urine CRH IR (r=0.25, p > 0.1) further indicate CRH degradation. Plasma and spot urinary CRH IR, however, were strongly correlated (r=0.80, p=0.001). The total CRH IR excreted as estimated from the spot urine value (0.5 ±0.1 (μg/day) compared with the total filtered load of CRH IR in the pregnant group (1306.9 ± 324.6 μg/day) showed that 99.97% of the filtered CRH IR was reabsorbed or metabolized by the kidneys. Acidic gel chromatography of spot and 24-hour urine samples showed a CRH IR peak at CRH41 standard elution position (K_d=0.5), indicating that the molecular form in urine is similar to the 41-residue standard. Pregnancy-induced hypertension correlated positively with plasma CRH IR (r=0.62, p < 0.001) and spot urine CRH IR (r=0.46, p < 0.01), and negatively with parity (r=-0.60, p < 0.001). Plasma CRH IR and parity also negatively correlated (r=-0.41, p < 0.05). Gel chromatography, using neutral buffer, of urine samples incubated with radiolabeled [¹²⁵I]TyrCRH showed that the high affinity, high specificity binding protein which was present in human plasma subjected to the same treatment was not present in urine. These data constitute the first report on urinary CRH IR during pregnancy. The results indicate that spot urine might be a useful measure of the biological levels of the hormone in pregnancy as it appears not to harbour any apparent binding protein.