Gestational Stress Impairs Postpartum Endothelial Function in Rats, Study Finds

Exposure to variable stress during the final week of pregnancy induces enduring vascular and metabolic impairments in female Wistar rats that persist through the postpartum lactation period, according to an experimental investigation conducted by researchers at the Fluminense Federal University. The findings reveal that maternal exposure to unpredictable psychological and environmental stressors during late gestation leads to significant vascular hyperreactivity to vasoconstrictor stimuli, an approximate 25 percent reduction in endothelium-dependent maximal vasodilation, elevated circulating corticosterone concentrations, and decreased expression of the active phosphorylated form of endothelial nitric oxide synthase within the thoracic aorta.

While stress represents a natural adaptive physiological response to internal or external challenges, chronic exposure to stressors has been consistently identified as a substantial risk factor for the progression and development of cardiovascular disease, insulin resistance, and various metabolic disorders. Pregnancy constitutes a unique physiological state defined by profound hormonal, autonomic, and cardiovascular adaptations, accompanied by elevated baseline metabolic demands and an intrinsic increase in the production of reactive oxygen species. Although earlier research has established that female rodents typically display a greater capacity to preserve endothelial function relative to males due to the vasoprotective actions of estrogen, the extent to which gestational stress disrupts maternal vascular homeostasis in the postpartum period remained largely uncharacterized.

To investigate these physiological repercussions, the researchers evaluated female Wistar rats (Rattus norvegicus, albinus variety) maintained under standardized vivarium conditions at 24 degrees Celsius with regular twelve-hour light-dark cycles. Following confirmed mating and pregnancy verification via vaginal lavage or the detection of a vaginal plug, pregnant dams were assigned either to an unstressed control group or to a variable stress cohort. The stressed animals were subjected daily to a variable stress regimen across the third gestational week, specifically spanning gestational days 14 through 21, consisting of four distinct stress paradigms administered non-consecutively: 60-minute isolation, exposure to wet sawdust for 24 hours, 24-hour cage tilting by 5 centimeters, and six-hour food and water deprivation.

Following parturition, both groups of dams were systematically monitored throughout the 21-day lactation window under ad libitum access to standard rodent chow and water. Maternal blood and vascular tissues were harvested upon study completion at the conclusion of lactation, following an overnight six-hour fast and surgical anesthesia with ketamine and xylazine. Efficacy of the gestational stress protocol was validated by measuring maternal serum corticosterone concentrations via chemiluminescence enzyme-linked immunosorbent assay. The stressed dams exhibited significantly higher circulating corticosterone levels, averaging 3.38 nanograms per milliliter compared to 1.50 nanograms per milliliter in control mothers, confirming sustained neuroendocrine hypothalamic-pituitary-adrenal axis activation.

The experimental stress protocol also produced distinct somatic and metabolic alterations across the gestational and postpartum timeline. Mothers subjected to gestational variable stress demonstrated significantly greater cumulative body mass gain from the beginning of gestation until the end of lactation, gaining an average of 45.94 grams compared to 33.89 grams in the control cohort. This difference occurred despite both groups exhibiting equivalent total food consumption and caloric intake during pregnancy, indicating that stress exposure fundamentally disrupted maternal energy balance and metabolic efficiency rather than merely altering ingestive behavior. While circulating blood glucose levels were significantly lower in stressed dams immediately following the stress protocol at the conclusion of gestation, blood glucose values normalized and showed no significant difference between cohorts by the end of the lactation period.

Lipid profiling performed at the study terminus demonstrated a selective impact on high-density lipoprotein cholesterol concentrations without significantly modifying other circulating lipid fractions. Serum high-density lipoprotein cholesterol was markedly lower in the variable stress group, registering 35.02 milligrams per deciliter compared to 48.95 milligrams per deciliter in controls. In contrast, circulating total cholesterol, low-density lipoprotein cholesterol, and triglycerides showed no statistically significant differences between the two maternal groups. Examination of neonatal parameters revealed that while overall litter size and offspring sex distribution remained unaltered by gestational stress, both female and male pups born to stressed mothers exhibited significantly lower birth weights compared to control offspring.

Functional evaluation of vascular reactivity was conducted in isolated thoracic aortic rings mounted in organ chambers filled with physiological Krebs solution continuously aerated with oxygen and carbon dioxide. Aortic segments from stressed dams displayed marked vascular hyperreactivity when stimulated with the alpha-adrenergic agonist phenylephrine, evidenced by a significantly increased sensitivity and higher pEC50 value of 7.17 compared to 6.47 in controls. Concurrently, endothelium-dependent relaxation elicited by cumulative concentrations of acetylcholine was substantially diminished; aortic rings from stressed mothers achieved a maximal relaxation response of 78.79 percent compared to 104.0 percent in control dams, reflecting an absolute reduction in vasodilatory capacity of 25.21 percent.

Hemostatic evaluation using turbidimetric lumi-aggregometry revealed that gestational stress provoked a prothrombotic alterations in maternal circulation. When platelet-rich plasma was stimulated with 0.5 micromolar adenosine diphosphate, platelets isolated from the variable stress group displayed a significantly higher percentage of ex vivo aggregation, reaching 47.40 percent compared to 43.00 percent in control dams. In systemic antioxidant evaluations, plasma activities of superoxide dismutase and catalase demonstrated no significant differences between the experimental cohorts. However, Western blot quantification of vascular tissue lysates revealed that thoracic aortas from stressed animals had significantly reduced protein expression of catalase and a trend toward lower superoxide dismutase expression, pointing to a localized impairment of vascular antioxidant defense mechanisms.

Molecular analysis of vascular nitric oxide pathways provided mechanistic insight into the observed loss of endothelial relaxation. While total endothelial nitric oxide synthase protein abundance remained comparable between cohorts, the thoracic aorta of stressed dams exhibited a significant decrease in the active phosphorylated form of the enzyme at serine 1177, measuring 0.66 arbitrary units versus 1.20 arbitrary units in controls. Phosphorylation of this residue is critical for activating the enzyme to synthesize nitric oxide, a primary mediator of endothelium-dependent vasodilation that preserves vascular tone and counters platelet activation. The concurrent reduction in active nitric oxide synthase and localized antioxidant enzymes supports the role of vascular redox imbalance and impaired nitric oxide bioavailability in driving vascular dysfunction.

The study authors noted that direct pharmacological inhibition of nitric oxide synthase was not performed in the functional vascular organ chamber experiments, which represents a methodological limitation in establishing the isolated contribution of nitric oxide. Nevertheless, the coherent alignment of decreased serine-phosphorylated endothelial nitric oxide synthase with depressed maximal acetylcholine-induced vasodilation, heightened vasoconstrictor sensitivity, lowered high-density lipoprotein cholesterol, and heightened platelet aggregation highlights widespread, persistent maternal cardiovascular consequences. By demonstrating that late gestational stress leaves measurable vascular and hemostatic impairments that endure beyond the conclusion of lactation, the research underscores the vulnerability of maternal physiology during gestation and provides foundational evidence for future studies examining postpartum vascular health.

The observed elevation in platelet aggregation carries notable relevance when considered alongside the normal hemostatic changes of pregnancy. During gestation, maternal physiology naturally adopts a prothrombotic state through increased concentrations of coagulation factors VII, VIII, and X and fibrinogen, accompanied by decreases in protein S activity and fibrinolysis to manage bleeding during childbirth. This adaptive shift elevates baseline thromboembolic susceptibility, which becomes particularly critical during the postpartum period when pulmonary embolism is a leading cause of maternal mortality in developed countries. The researchers underscored that when stress-induced platelet hyperaggregability coincides with impaired vascular reactivity, the resulting changes in vascular tone and venous return may further compound maternal vulnerability to pathological thrombus formation.

The heightened aortic sensitivity to phenylephrine similarly reflects disrupted neuroendocrine control over vascular tone. In healthy cardiovascular homeostasis, vascular tone is maintained through an equilibrium between vasodilatory mechanisms and alpha-adrenergic vasoconstriction. Under variable gestational stress, sustained activation of the sympathetic nervous system stimulates the synthesis and release of catecholamines, specifically norepinephrine and epinephrine, which bind alpha-adrenergic receptors to trigger vasoconstriction. While alpha-adrenergic constriction represents an essential autonomic survival mechanism during acute challenges such as hemorrhage or hypothermia, chronic adrenergic stimulation induces vascular hyperreactivity. Combined with impaired endothelial cell turnover, diminished nitric oxide availability, and decreased nitric oxide synthase expression, this adrenergic overdrive fosters sustained vascular tone elevation and heightened susceptibility to cardiovascular disease.

The divergence between systemic circulating enzyme activity and aortic protein expression provides additional nuance regarding gestational redox biology. Although circulating plasma activities of superoxide dismutase (6.81 units per milliliter in stressed rats compared to 6.82 units per milliliter in controls) and catalase (9.61 versus 10.41 nanomoles per minute per milliliter) showed no statistical differences between groups, prior research demonstrates that circulating antioxidant enzymes naturally decrease throughout pregnancy, an effect that may have obscured systemic stress impacts. Within the aortic tissue itself, however, Western blot analysis demonstrated a significant drop in catalase protein expression to 0.17 arbitrary units in stressed animals compared to 1.00 in controls, alongside a trend toward reduced superoxide dismutase expression (0.25 versus 1.00 arbitrary units) and stable glutathione peroxidase levels (0.67 versus 1.00 arbitrary units). Concurrently, while glucocorticoid release typically elevates blood glucose by stimulating gluconeogenesis and impeding adipose glucose uptake, post-stress glucose fell transiently to 74.57 milligrams per deciliter compared to 84.00 in controls before equalizing after lactation. The authors noted that such metabolic and redox disparities reflect the complex physiological interplay between breeding background, rodent lineage, and localized vascular defense deterioration.

Subject of Research: Postpartum maternal vascular and endothelial dysfunction induced by late gestational stress in rats

Article Title: Impact of gestational stress on postpartum endothelial function

Article References: de Souza, P. R., de Souza Monnerat, J. A., Luchetti, B. B., Mentzinger, J., Teixeira, G. F., Rocha, H. N. M., de Brito, F. C. F., Lima, G. F., da Motta, N. A. V., Manhães, A. C., Macedo, V. N., Rocha, N. G., da Nóbrega, A. C. L., & Medeiros, R. F. (2026). Impact of gestational stress on postpartum endothelial function. Physiological Reports, 14(21), Article e71171. https://doi.org/10.14814/phy2.71171

Image Credits: AI Generated

DOI: 10.14814/phy2.71171

Keywords: gestational stress, endothelial function, postpartum vascular reactivity, endothelial nitric oxide synthase, platelet aggregation, Wistar rats, corticosterone, thoracic aorta, acetylcholine relaxation, phenylephrine hyperreactivity, HDL cholesterol, oxidative stress, catalase, maternal cardiovascular health, birth weight