Fetal breathing, sleep state and cardiovascular adaptations to anaemia in sheep

Sheep Nocturnal Activity Dataset

Monitoring sheep’s behavior is of paramount importance, because deviations from normal patterns may indicate nutritional, thermal or social stress, changes in reproductive status, health issues, or predator attacks. The night period, despite being a more restful period in which animals are theoretically sleeping and resting, represents approximately half of the life cycle of animals; therefore, its study is of immense interest. Wearable sensors have become a widely recognized technique for monitoring activity, both for their precision and the ease with which the sensorized data can be analyzed. The present dataset consists of data from the sensorization of 18 Serra da Estrela sheep, during the nocturnal period between 18 November 2021 and 16 February 2022. The data contain measurements taken by ultrasound and accelerometry of the height from neck to ground, as well as measurements taken by an accelerometer in the monitoring collar. Data were collected every 10 s when the animals were in the shelter. With the collection of data from various sensors, active and inactive periods can be identified throughout the night, quantifying the number and average time of those periods.

The effect of adrenalectomy on the cardiac response to subacute fetal anemia

The mechanisms that stimulate fetal heart growth during anemia are unknown. To examine the hypothesis that adrenal hormones contribute to this process, we determined the effects of adrenalectomy (Adx) on heart growth and the activation of cardiac mitogen-activated protein kinases (MAPKs) in the presence and absence of fetal anemia. To identify mechanisms contributing to the initiation of cardiac growth, the duration of anemia was limited to a period shorter than that previously described to result in increased cardiac mass. Four groups of fetal sheep were studied (Adx-Anemic, Adx-Control, Intact-Anemic, Intact-Control). Anemia was created by daily controlled hemorrhage for 5 days; hearts were collected for analysis at 133 d gestation (term 145 d). Cardiomyocyte morphometry, immunohistochemistry for Ki-67 (proliferation marker), and Western blotting for protein levels of MAPKs and proliferating cell nuclear antigen (PCNA) were performed. Blood pressure, heart rate, heart weight-to-body weight ratio, and cardiomyocyte length and width remained similar among groups throughout the study. PCNA levels in the Adx-Anemic group were twice as high as in any other group (both ventricles, p < 0.05). Levels of phosphorylated extracellular signal-regulated kinase (ERK) were ~60% higher in the Intact-Anemic and Adx-Anemic groups, compared with the Intact-Control and Adx-Control groups (p < 0.02). These results suggest that adrenal hormones may attenuate fetal cardiomyocyte proliferation in response to anemia (as evidenced by the increased PCNA in Adx-Anemic fetuses) and that phosphorylation of myocardial ERK results from fetal anemia, irrespective of the status of the fetal adrenal gland.

Cardiomyocyte enlargement, proliferation and maturation during chronic fetal anaemia in sheep

Chronic anaemia increases the workload of the growing fetal heart, leading to cardiac enlargement. To determine which cellular process increases cardiac mass, we measured cardiomyocyte sizes, binucleation as an index of terminal differentiation, and tissue volume fractions in hearts from control and anaemic fetal sheep. Fourteen chronically catheterized fetal sheep at 129 days gestation had blood withdrawn for 9 days to cause severe anaemia; 14 control fetuses were of similar age. At postmortem examination, hearts were either enzymatically dissociated or fixed for morphometric analysis. Daily isovolumetric haemorrhage reduced fetal haematocrit from a baseline value of 35% to 15% on the final day (P < 0.001). At the study conclusion, anaemic fetuses had lower arterial pressures than control fetuses (P < 0.05). Heart weights were increased by 39% in anaemic fetuses compared with control hearts (P < 0.0001), although the groups had similar body weights; the heart weight difference was not due to increased ventricular wall water content or disproportionate non-myocyte tissue expansion. Cardiomyocytes from anaemic fetuses tended to be larger than those of control fetuses. There were no statistically significant differences between groups in the cardiomyocyte cell cycle activity. The degree of terminal differentiation was greater in the right ventricle of anaemic compared with control fetuses by 8% (P < 0.05). Anaemia substantially increased heart weight in fetal sheep. The volume proportions of connective and vascular tissue were unchanged. Cardiomyocyte mass expanded by a balanced combination of cellular enlargement, increased terminal differentiation and accelerated proliferation.

Assessment of fetal heart rate and fetal movements in detecting oxygen deprivation in-utero

This article reviews the physiological principles underlying the application of assessment of fetal movements and fetal heart rate (FHR) in detecting fetal hypoxia. Studies in both fetal sheep and healthy human fetuses are discussed including those which have demonstrated the importance of appreciating the existence of rest-activity cycles under normal physiological conditions. The role of adenosine in mediating the hypoxic inhibition of fetal breathing movements (FBMs) is reviewed as is the previously unrecognized importance of fetal gasping as a possible new measure of fetal hypoxia.

Fetal cardiovascular and breathing responses to an adenosine A2a receptor agonist in sheep

CGS-21680 (CGS), a highly selective adenosine A2a receptor agonist, may excite the fetal carotid bodies. This study was designed to determine 1) whether CGS stimulates fetal breathing and 2) whether sinoaortic denervation abolishes CGS-induced tachycardia. In eight intact fetuses (> 0.8 term), intra-arterial CGS infusion (6 micrograms.min-1.kg estimated fetal wt-1) increased mean arterial PCO2 by 3-7 Torr, reduced fetal arterial PO2 by 2-5 Torr, and produced a mild metabolic acidemia. Heart rate increased from 154 +/- 7 (control) to 249 +/- 12 beats/min, but mean arterial pressure was not significantly affected. CGS initially increased the frequency, amplitude, and incidence of fetal breathing, but this hyperpnea was followed by prolonged respiratory depression that was not reversed with blockade of adenosine A1 receptors. Denervation of both carotid bodies together with interruption of the vagi abolished the hyperpnea without altering the respiratory depression or the maximum rise in heart rate. We conclude that CGS induces 1) tachycardia by a mechanism independent of the peripheral arterial chemoreceptors, 2) hyperpnea by stimulating peripheral adenosine A2a receptors, and 3) respiratory depression by activating central A2a receptors.

Changes in ovine fetal adrenocortical responsiveness after long-term hypoxemia

This study tested the hypothesis that in the fetus long-term hypoxemia induces premature adrenocortical maturation and augments adrenal responsiveness to adrenocorticotropin hormone (ACTH). Pregnant ewes were exposed to high altitude (3,820 m) from 30 to 120 days gestation, when surgery was performed. Maternal arterial pressure of O2 (PaO2) was maintained at approximately 60 Torr by N2 infusion through a tracheal catheter. Fetal PaO2 was significantly lower in the hypoxemic (21 +/- 0.2 Torr) vs. normoxic (26 +/- 0.4 Torr) fetuses (P < 0.01). Between 125 and 140 days, basal ACTH and cortisol concentrations were similar in both groups. To assess changes in adrenal responsiveness, we challenged the fetuses with ACTH (100 ng/kg body wt, iv bolus) at 126 and 136 days. At 126 days, after ACTH challenge, fetal plasma ACTH peaked at similar values (275 +/- 43 and 250 +/- 26 pg/ml) in normoxic and hypoxemic fetuses, respectively. Plasma cortisol subsequently increased to 84 +/- 8 and 44 +/- 6 ng/ml in these groups. At 136 days, after ACTH challenge, plasma ACTH peaked at 379 +/- 57 and 336 +/- 21 pg/ml in normoxic and hypoxemic fetuses, respectively. Although plasma cortisol concentration in normoxic fetuses increased to 180 +/- 21 ng/ml, levels in hypoxemic fetuses only reached 62 +/- 12 ng/ml (P < 0.05 compared with normoxic). Catecholamine concentrations were not significantly different between the two groups. These data do not support the hypothesis that adrenocortical maturation occurs prematurely, augmenting adrenal responsiveness to ACTH after exposure to long-term hypoxemia. Rather, the ability of the fetus to respond to an ACTH challenge is blunted.

Anemia up-regulates pontine A1 adenosine receptors in fetal sheep

A rise in central adenosine concentrations most likely triggers the inhibitory effects of acute hypoxia on fetal breathing movements. During prolonged O2 deficiency, the incidence of fetal breathing increases over time, an adaptation which may involve down-regulation of adenosine receptors. Therefore, isovolemic anemia was induced in chronically catheterized fetal sheep to determine the effects of acute O2 deprivation on the affinity of brainstem A1 adenosine receptors. Compared to control values, the mean hemoglobin concentration in 4 fetuses was lowered by 54% (to 3.7 +/- 0.4 g/dl) for 1 h and in 3 fetuses by 58% (to 3.8 +/- 0.6 g/dl) for 4 h. Mean preductal arterial pH during anemia was significantly reduced to values as low as 7.123 +/- 0.090, but mean paO2 and paCO2 were not significantly affected. The average incidence of fetal breathing movements was decreased by 80% during the first hour and by 50% during the fourth hour of anemia. In 3 fetuses with normal hemoglobin levels, about 32 +/- 6.0% of the A1 adenosine receptors in the brainstem were in the high affinity state. After 1 h of anemia, the percentage of high affinity receptors in the pons (but not medulla or midbrain) had significantly increased to 47 +/- 2.9%, but after 4 h of anemia all 3 brainstem regions had A1 receptor affinity within the range of control values. It is concluded that acute anemia induces a short-lived up-regulation of pontine A1 adenosine receptors, but anemia does not alter A1 receptor coupling in the midbrain where A1 receptors related to breathing inhibition may be located.