ABSTRACT
Melatonin production is regulated by both catecholamines and sympathetic activity.
Urine levels of the major metabolite of melatonin, 6-sulfatoxymelatonin, correlate
well with serum melatonin levels and have been used to evaluate sympathetic output.
We tested the hypothesis that urinary levels of 6-sulfatoxymelatonin would reflect
the change in adrenergic activity on working days compared with nonworking days during
pregnancy. Twenty-three healthy pregnant women, employed in a variety of occupations,
including physicians, nurses, secretaries, salespeople, and laboratory workers were
recruited from the clinics of the University of North Carolina School of Medicine.
We measured 6-sulfatoxymelatonin levels in first morning voids and for the subsequent
10 hours at 24, 28, 32, and 36 weeks' gestation. Urine was collected in sets during
working days and during nonworking days. 6-Sulfatoxymelatonin was measured by radioimmunoassay.
In 11 women we also measured urine catecholamines by high-performance liquid chromatography.
Levels of 6-sulfatoxymelatonin output did not change across gestation, although they
tended to drift down as pregnancy progressed. Median levels at first morning void
were 6.3 μg on workdays and 4.6 μg on nonwork-days. Although all values were skewed
toward work being greater than nonwork, there were large interindividual variations.
We therefore compared subjects against themselves and compared work levels for each
subject to the corresponding gestational age-matched nonwork value. Among the 23 women,
median 6-sulfatoxymelatonin levels were 81% greater during work than nonwork (p <0.0002) when first morning collections were compared. Daytime urinary excretion
of 6-sulfatoxymelatonin on workdays was 38% (p <0.005) greater than during nonworkdays. As expected, both epinephrine and norepinephrine
levels were higher on workdays than nonworkdays, 93% greater (p <0.001) and 52% (p <0.001), respectively. In this subset of women the 6-sulfatoxymelatonin levels were
106% higher on workdays compared with nonworkdays (p <0.002). Melatonin secretion reflected the differences in adrenergic activity between
workdays and nonworkdays. Because levels were fairly constant across gestation, 6-sulfatoxymelatonin
may have potential as a biologic marker for some aspects of stress in pregnancy and
may be useful for studies evaluating the relationship between work and pregnancy outcomes.
However, because of large interindividual variations, subjects will have to be compared
against themselves.
Keywords
Stress - melatonin - catecholamines
