Clinical biochemistry of pregnancy

Pregnancy at high altitude: a hyperviscosity state

BACKGROUND

Pregnancy at high altitude has been associated with intrauterine growth restriction and preeclampsia. These conditions, at sea level, have been linked to increased hematocrit and blood viscosity. The aim of this study was to investigate the effect of high altitude on maternal hemorheology.

METHODS

This was a cross-sectional study. We examined 94 pregnant women at 10-38 weeks of gestation resident at high altitude (4370 m above sea level) and 75 at sea level, and 24 and 17 nonpregnant women at each altitude, respectively. Blood and plasma viscosity, hematocrit, plasma fibrinogen, albumin and total protein concentrations were determined in blood samples obtained after an overnight period of fasting.

RESULTS

Pregnancy at high altitude, compared to sea level, is characterized by higher hematocrit, blood viscosity (at high shear rate), plasma viscosity, total protein and fibrinogen concentrations (25%, 38%, 7%, 13.3% and 25%, respectively) and 6% lower albumin concentration. Nonpregnant women at high altitude, compared to sea level, had higher hematocrits, blood viscosity, plasma viscosity, total protein and fibrinogen concentrations (25%, 55%, 18%, 26% and 98%, respectively) and 13% lower albumin concentration.

CONCLUSION

Pregnancy at high altitude compared to sea level is characterized by increased blood viscosity as a result of increased hematocrit and plasma viscosity.

Female Sex Steroid Hormones and Pregnancy Regulate Receptors for Calcitonin Gene-Related Peptide in Rat Mesenteric Arteries, but Not in Aorta1

Calcitonin gene-related peptide (CGRP) is a potent vasodilator neuropeptide known to be involved in the regulation of vascular tone. Results of previous studies from our laboratory and others suggest that vascular sensitivity to CGRP is enhanced during pregnancy and that the female sex steroid hormones estradiol-17beta (E2) and progesterone (P4) may be involved in this process. We hypothesized that CGRP receptors in the mesenteric artery are increased during pregnancy and with sex steroid hormone treatments. In the present study, we investigated whether pregnancy and female sex steroid hormones modulate the CGRP-receptors CGRP-A and CGRP-B in the mesenteric artery in the rat. The CGRP-A receptor consists of calcitonin receptor-like receptor (CRLR) and receptor activity-modifying protein 1 (RAMP1); however, the CGRP-B receptor needs to be further characterized. Messenger RNA levels for CRLR and RAMP1 were assessed by reverse transcription-polymerase chain reaction, and CGRP-B receptor proteins levels were determined by Western blot analysis. In addition, [125I]CGRP binding was measured by Scatchard analysis. Both mRNA for CGRP-A (CRLR and RAMP1) and the protein for CGRP-B receptors in mesenteric arteries were increased with pregnancy compared to nonpregnant, diestrous animals. A P4 antagonist, RU-486, downregulated and P4 upregulated these receptors in mesenteric arteries (P < 0.05) in pregnant rats. In adult ovariectomized rats, P4 upregulated CRLR and RAMP1 mRNA levels as well as [125I]CGRP-binding sites. The CGRP-B-receptor protein levels were significantly (P < 0.05) elevated by P4 and by combined E2 and P4 treatment. Together with earlier findings, these data suggest that increases in the expression of CGRP-A (CRLR and RAMP1) and CGRP-B receptors in mesenteric arteries may be important in reducing vascular resistance and in vascular adaptations that occur during pregnancy; in addition, P4 may be involved in this process.

Maternal electrolyte and liver function changes during pregnancy at high altitude

BACKGROUND

High-altitude (HA) hypoxia leads to profound cardiovascular, respiratory and electrolyte changes, and pregnancy at HA has been associated with increased incidence of preeclampsia and intrauterine growth restriction.

OBJECTIVE

To examine the effect of high altitude on maternal serum electrolytes and liver enzymes.

DESIGN

Cross-sectional study of 77 pregnant women at 6-40 weeks of gestation resident at HA (4370 m above sea level) and 80 at sea level (SL) and 13 and 15 nonpregnant women at each altitude, respectively. Serum electrolytes (sodium, potassium, calcium and phosphate), creatinine, bilirubin and liver enzymes (alkaline phosphatase (ALP), aspartate transaminase (AST) and gamma-glutamyl transferase (gamma-GT)) were measured.

RESULTS

Pregnancy at HA, compared to SL, was associated with higher serum osmolality (0.4%), sodium (0.7%), creatinine (14%) and phosphate (5%) concentrations and lower potassium (10%) concentration. Calcium and albumin-corrected calcium concentrations were higher at HA compared to SL in nonpregnant women (8%), with no difference in pregnant women. AST, gamma-GT and ALP concentrations were not significantly different between HA and SL, neither in pregnant nor in nonpregnant women. AST and gamma-GT were lower in pregnant compared to nonpregnant women (30%) at HA, whereas the difference was not significant at SL. Total bilirubin concentrations were higher at HA compared to SL by about 25% both in pregnant and in nonpregnant women, the difference reaching statistical significance only in the pregnant group.

CONCLUSIONS

Pregnancy at HA is associated with increased osmolality, sodium, creatinine, calcium, phosphate and total bilirubin concentrations. Liver enzyme activities are similar to SL.

Sex steroid hormones enhance hypotensive effects of calcitonin gene-related Peptide in aged female rats

The aim of the present study is to investigate whether vascular protective effects of steroid hormones in aged female rats are mediated through calcitonin gene-related peptide (CGRP), a known potent vasodilator. This rat model reflects the postmenopausal state in humans. We examined whether blood pressure lowering effects of CGRP are enhanced in aged female rats when steroid hormone treatments are administered. We observed that 1) continuous infusion of CGRP lowered blood pressures in rats treated with estradiol-17beta and progesterone (P < 0.05), 2) acute hypotensive effects of CGRP were significantly (P < 0.05) greater in the presence of steroid hormones than in vehicle-treated groups, 3) blood pressure decreases in response to CGRP are lower in aged female rats than they are in young adult ovariectomized rats, and 4) age-related differences in the hypotensive effects of CGRP were nullified when animals were treated with steroid hormones. These data suggest that female sex steroid hormones may modulate arterial blood pressure by regulating the CGRP effector system in female rats regardless of age.

Gestational changes in calcitonin gene-related peptide, nerve growth factor, and its receptors in rat dorsal root ganglia

In dorsal root ganglia (DRG) cell cultures, levels of calcitonin gene-related peptide (CGRP) are increased in the presence of ovarian hormones and nerve growth factor (NGF). In addition, injection of ovariectomized rats with ovarian hormones led to an increase in levels of two NGF receptors, TrkA and p75(NTR), in DRG. Thus, we hypothesized that increased levels of ovarian hormones during pregnancy may elevate the synthesis of CGRP and NGF receptors in the DRG. DRG harvested from rats on specific days of pregnancy, on Day 2 postpartum, and after ovariectomy were subjected to radioimmunoassay, Western blot analysis, and NGF immunoassay to determine levels of CGRP, TrkA and p75(NTR), and NGF, respectively. CGRP levels in rat DRG were significantly higher during pregnancy than at Day 2 postpartum or in ovariectomized rats. Levels of both TrkA and p75(NTR) in DRG increased during pregnancy and remained elevated at Day 2 postpartum, but CGRP levels declined. Levels of NGF reached a statistically significant peak at Day 18 of gestation, and were not significantly reduced at Day 2 postpartum. Increased levels of ovarian steroid hormones during pregnancy may be involved in the synthesis of CGRP, however, the postpartum decreases in CGRP synthesis appear to be unrelated to NGF and its receptors.

Serum concentrations of retinol, alpha-tocopherol and the carotenoids are influenced by diet, race and obesity in a sample of healthy adolescents

An important part of understanding the functions of vitamin A, vitamin E and the carotenoids in nutritional status assessment, health promotion and disease prevention is knowledge of factors that influence their distribution in human tissues. Our objective was to examine serum concentrations of these nutrients and compounds in a sample of 285 healthy participants, 12-17 y old, from three U. S. cities. Pearson correlations between diet measured with a food frequency questionnaire and serum nutrient concentrations among these adolescents (adjusted for total serum cholesterol, age, sex, race and body mass index) were as follows: retinol, 0.23; alpha-tocopherol, 0.16; alpha-carotene, 0.31; beta-carotene, 0.15; beta-cryptoxanthin, 0.38; lycopene, 0.08; and lutein + zeaxanthin, 0.25. Multivariate linear regression modeled associations of demographic, dietary and physiologic variables with serum concentrations of these nutrients. African-American participants had significantly lower concentrations of serum retinol (P < 0.001), alpha-tocopherol (P < 0.01) and alpha-carotene (P < 0.02), but higher concentrations of lutein + zeaxanthin (P = 0.001) compared with Caucasians. Obese participants had serum nutrient concentrations that were 2-10% (P < 0.05) lower than normal weight participants. Dietary intake was a significant predictor of all serum analytes (P < 0.01) except lycopene. These models explained 20% of the variability in serum retinol, 28% of the variability in serum alpha-tocopherol, and 14-24% of the variability in serum carotenoids.

Haemorheological adaptation during pregnancy in a Latin American population

OBJECTIVE

To investigate haemorheological changes during pregnancy in a Latin American population and compare to previously published data from Caucasian populations.

DESIGN

Cross-sectional study.

POPULATION

75 pregnant women at 10-36 wk of gestation and 17 non-pregnant female controls in Lima, Peru. All the women and their ancestors for three generations were born and lived at sea level.

METHODS

Viscosity, haematocrit and plasma fibrinogen, albumin and total protein concentrations were determined in blood samples obtained after an overnight period of fasting.

RESULTS

At 10 wk of gestation, total protein concentration and plasma viscosity were above non-pregnant levels by about 15% and subsequently decreased linearly with gestation. Fibrinogen concentration was increased in the first trimester; it then decreased to a nadir at about 20 wk and subsequently increased. Albumin concentration decreased linearly with gestation. Haematocrit decreased from pre-pregnancy levels at 10 wk to a nadir at about 26 wk. Blood viscosity increased in the first trimester and then decreased with gestation to a nadir at about 26 wk.

CONCLUSION

In the first trimester of pregnancy blood and plasma viscosity are increased and they subsequently fall with advancing gestation. Plasma viscosity reflects the changes in total protein concentration, and blood viscosity is dependent on the interplay of changes in plasma viscosity and haematocrit.

Olestra consumption does not predict serum concentrations of carotenoids and fat-soluble vitamins in free-living humans: early results from the sentinel site of the olestra post-marketing surveillance study

In 1996, the U.S. Food and Drug Administration approved olestra, a fat substitute, for use in snack foods. Previous studies had shown that olestra consumption could reduce absorption of carotenoids and fat-soluble vitamins. To determine the association between consumption of olestra-containing snack foods and serum concentrations of carotenoids and fat-soluble vitamins in a free-living population, we interviewed independent population-based cross-sectional samples of 1043 adults before olestra was available and 933 adults 9 mo after olestra snacks were introduced into the marketplace in Marion County, IN, the first major test market for olestra. A cohort composed of 403 adults from the first survey, oversampling those most frequently reporting olestra consumption during follow-up telephone interviews, completed a second survey. We assessed diet, lifestyle factors and olestra consumption, and collected blood for assays for the serum concentrations of six carotenoids, four fat-soluble vitamins and lipids. Nine months after the introduction of olestra into the marketplace, 15.5% of Marion County residents reported consuming an olestra-containing snack in the previous month, with a median frequency among consumers of 3.0 times per month. There were no significant associations or consistent trends for decreased serum carotenoids or fat-soluble vitamins associated with olestra consumption, although cohort members consuming >/=2 g/d of olestra had adjusted total serum carotenoids 15% lower compared with baseline. There were increases in serum vitamin K concentrations associated with olestra consumption (P = 0.03 in the cross section and P = 0.06 in the cohort). In summary, there was no statistically significant evidence in this free-living population of associations between olestra consumption and decreased serum concentrations of carotenoids and fat-soluble vitamins.

Baroreceptor afferent discharge in the pregnant rat

Pregnancy is associated with blunted reflex responses to cardiac and arterial baroreceptor stimulation. We tested the hypothesis that arterial baroreceptor afferent discharge is attenuated in response to a pressure stimulus in pregnant rats. Multifiber aortic depressor nerve activity (ADNA), mean arterial pressure (MAP), and heart rate were measured in anesthetized (pentobarbital sodium, 35 mg/kg ip) late-pregnant and virgin rats in response to increases ¿phenylephrine (PE), 1.5-24 microg. kg(-1). min(-1) and 1-16 microg/kg and decreases ¿sodium nitroprusside (SNP), 5-80 microg. kg(-1). min(-1) and 0.05-16 microg/kg in MAP. Resting MAP was lower in pregnant rats, but changes in MAP were similar to those in virgin rats during both PE and SNP administration. ADNA was significantly attenuated in pregnant animals during both PE and SNP infusions (P < 0.05) due to a more rapid adaptation to the pressure stimulus. Bolus drug administration evoked similar changes in MAP and ADNA in both groups; however, the maximum decrease in ADNA was achieved at the lowest dose of SNP in pregnant rats. Thus baroreceptor afferent discharge is attenuated in pregnant rats, and this involves a more rapid adaptation to a pressure stimulus.

Regulation of calcitonin gene-related peptide expression in dorsal root ganglia of rats by female sex steroid hormones

Calcitonin gene-related peptide (CGRP), a potent vasodilator primarily synthesized in dorsal root ganglia (DRG) neurons, has been shown to decrease vascular resistance and thus regulate blood flow to a variety of organs in rats. Serum CGRP levels in the human have been reported to increase with pregnancy and decrease postpartum. It has been suggested that female sex steroid hormones play a role in cardiovascular function, but the mechanisms are unknown. In this study, we examined the effects of estradiol-17beta (E(2)) and progesterone (P(4)) on the expression of CGRP in DRG in adult rats both in vivo and in vitro. Ovariectomized (ovx) animals were injected s.c. with 5 microg E(2), 4 mg P(4), or 5.0 microg E(2) + 4 mg P(4) in 0.5 ml sesame oil or with oil only, and groups of 4 rats were killed at 0, 24, or 48 h. DRGs were then removed and analyzed for CGRP mRNA and immunoreactive (i-)CGRP content by Northern blotting and RIA, respectively. Primary cultures of DRG neurons from adult female rats were used to assess the effects of varying doses of E(2) (1, 10, 100 nM), P(4) (10, 100, 1000 nM), or E(2) (10 nM) + P(4) (100 nM) in the absence or presence of nerve growth factor (NGF; 20 ng/ml); and CGRP mRNA content in the cells and i-CGRP in the medium were quantitated at 24 or 48 h after incubation. Results of in vivo studies showed that E(2) caused a significant increase in CGRP mRNA at 24 h (1.8-fold) and in i-CGRP levels both at 24 h (2. 8-fold) and at 48 h (3.4-fold) in DRG of ovx rats. P(4) also stimulated expression of both CGRP mRNA and i-CGRP. In the in vitro studies, either E(2) or P(4) alone or the two in combination were without effect on CGRP expression in cultured DRG neurons at all the doses tested. However, in the presence of NGF, both CGRP mRNA and peptide levels were significantly enhanced by E(2), P(4), and E(2)+P(4) in a time-dependent (2.0- to 2.8-fold at 24 h, 3.0- to 5. 0-fold at 48 h) and dose-dependent manner, with maximal effects achieved at 1.0 nM (E(2)) and 100 nM (P(4)) at 24 h of incubation. In summary, both E(2) and P(4), either alone or in combination, stimulate CGRP peptide synthesis in DRG neurons through increasing CGRP mRNA. The effects of these steroid hormones are mediated through amplifying the NGF-induced synthesis of CGRP in these neurons. Thus, we propose that the cardiovascular functions of female sex steroid hormones may be mediated, at least in part, by the up-regulation of neuronal CGRP synthesis, via NGF-mediated mechanisms.

Effects of calcitonin gene-related peptide on vascular resistance in rats: role of sex steroids

It has been demonstrated in reflex-intact animals that the sensitivity to calcitonin gene-related peptide (CGRP) is increased during pregnancy and that this action is mediated by sex steroids but not by nitric oxide (NO). We assessed the effects of CGRP in the following groups of anesthetized ganglion-blocked rats: 1) pregnant, 2) ovariectomized, and 3) ovariectomized and treated with estradiol and progesterone. Changes in mean arterial pressure (MAP) were assessed after the administration of varying doses of CGRP. Decreases in MAP after CGRP administration were significantly greater in pregnant rats and ovariectomized rats administered sex steroids than in ovariectomized controls. The CGRP antagonist CGRP8-37 produced a pressor response of similar magnitude in both pregnant and ovariectomized rats. We also assessed the effects of CGRP and the modulating role of NO in the isolated uterine vascular bed preparation. CGRP reduced perfusion pressure to a greater degree in ovariectomized animals treated with sex steroids than in ovariectomized animals. This response was attenuated by pretreatment with an NO synthesis inhibitor. CGRP8-37 produced a similar increase in perfusion pressure in both groups. We conclude that 1) the increased vascular sensitivity observed during pregnancy or after treatment with sex steroids is in part mediated by NO, and 2) CGRP8-37 has a vasoconstrictor action of its own.

Pregnancy and steroid hormones enhance the vasodilation responses to CGRP in rats

We recently reported that calcitonin gene-related peptide (CGRP) reversed the hypertension induced by nitric oxide inhibition in pregnant rats and that this effect appeared to be progesterone dependent. In the present study, we examined whether the vasodilator responses to CGRP are increased during pregnancy and whether these responses are steroid hormone dependent. Three groups of ovariectomized (Ovx) rats (n = 4-8 rats/group) were studied 3 days after daily treatment (subcutaneous injection) with progesterone (P; 2 mg/injection, twice daily for 3 days, in 0.2 ml of sesame oil), 17beta-estradiol (E; 2.5 microgram/injection, twice daily for 3 days, in 0.2 ml of sesame oil), or vehicle (sesame oil). A fourth group (n = 6 rats) of pregnant rats was studied on day 19 of gestation. A fifth group of adult, nonpregnant rats (n = 6 rats), regardless of stage of estrous cycle, was also used in this study. Mean arterial blood pressure (MAP) was continuously monitored in fully awake and free-moving instrumented rats. MAP was measured before and after administration of either saline or varying bolus doses of CGRP (9-360 pmol/kg body wt). CGRP produced a dose-dependent decrease in MAP in all rats with a significant (P < 0.05) reduction in MAP beginning with a CGRP dose of 90 pmol/kg and with maximal effects observed at 360 pmol/kg. Decreases in MAP in response to CGRP were significantly (P < 0.05) greater in pregnant compared with nonpregnant rats. Similarly to pregnant rats, Ovx rats given both E and P treatments produced greater decreases in MAP in response to CGRP at 90, 180, and 360 pmol/kg doses compared with both ovary-intact and Ovx nonpregnant rats, which were not different from each other. In summary, these data show that 1) the hypotensive effects of CGRP are dose dependent and 2) the hypotensive effects of CGRP are enhanced during pregnancy and in Ovx rats treated with either E or P. Therefore, we suggest that the decrease in vascular tone that is seen during pregnancy may be mediated, at least in part, by a sex steroid hormone-induced increase in the vascular sensitivity to the vasodilator effects of CGRP.

Severe rheumatoid arthritis prohibits the pregnancy-induced decrease in alpha3-fucosylation of alpha1-acid glycoprotein

Patients suffering from rheumatoid arthritis (RA) may experience a temporary reduction of disease symptoms during pregnancy. As indicated by the occurrence of RA-disease symptoms during pregnancy, three categories of patients were defined, namely, remission, relapse and unchanged. In all three categories changes in the plasma level and glycosylation of alpha1-acid glycoprotein (AGP) were determined longitudinally in comparison to those occurring in pregnancy of healthy women. In healthy pregnancy, we observed: (i) a peak in the plasma concentration at week 18 and a minimum at week 30; (ii) a continuous increase in the degree of branching of the glycans during the entire pregnancy period, and (iii) a decrease in the degree of alpha3-fucosylation of AGP-glycans with a minimum occurring at week 25. Comparable pregnancy-induced changes in glycosylation were found for two other acute-phase proteins alpha1-protease inhibitor (PI) and alpha1-antichymotrypsin (ACT). Increased oestrogen levels, known to occur during pregnancy, may be one of the factors that induce these changes, because the increased branching and decreased alpha3-fucosylation is in agreement with our earlier findings regarding an involvement of this hormone in the regulation of acute phase protein glycosylation in oestrogen-treated males as well as females. In all three clinical categories in RA, pregnancy also induced a continuous increase in the degree of branching of the glycans of AGP. However, similar changes in concentration and fucosylation were only found during remission of the disease symptoms. In the relapse and unchanged categories in RA, the degree of fucosylation and the plasma concentration of AGP remained constant throughout pregnancy. This indicates a relationship between changes in alpha3-fucosylation of AGP and RA disease activity.