Blood pressure and heart rate in the ovine fetus: ontogenic changes and effects of fetal adrenalectomy

Abstract

Ontogenic changes in baseline and 24-h rhythms of fetal arterial blood pressure (FABP) and heart rate (FHR) and their regulation by the fetal adrenal were studied in 18 fetal sheep chronically instrumented at 109–114 days gestation (GA). In the long-term study, FABP and FHR were continuously recorded from 120 days GA to spontaneous term labor (>145 days GA) in five animals. Peak times (PT) and amplitudes (Amp) of cosinor analysis were compared at 120–126, 127–133, and 134–140 days GA. Consistent, significant linear increases in FABP and linear decreases in FHR were observed in all fetuses. Significant 24-h rhythms in FABP and FHR were observed during all the time windows. In the adrenalectomy study, to test the hypothesis that fetal cortisol plays a key role in cardiovascular maturation, fetal adrenals were removed in eight animals (ADX); sham fetal adrenalectomy was performed on five animals (Con). Cortisol (4 μg/min) was infused intravenously in four ADX fetuses from day 7postsurgery for 7 days (ADX+F). No significant changes in PT and Amp in FABP and FHR were observed. Plasma cortisol levels remained low in Con and ADX fetuses (<4.9 ng/ml). Cortisol infusion increased fetal plasma cortisol to 22.3 ± 3.2 ng/ml (mean ± SE) on day 13 in ADX+F fetuses. FABP increased in control and ADX+F but not ADX fetuses; FHR decreased in control and ADX but rose in ADX+F fetuses. These results suggest that, in chronically instrumented fetal sheep at late gestation, 1) increases in FABP and decreases in FHR are maintained consistently from 120 to 140 days GA, with distinct 24-h rhythms, the PT and Amp of which remain unchanged, and 2) the physiological increase in FABP is dependent on the fetal adrenal; bilateral removal of the fetal adrenals does not prevent the ability of cortisol to produce a sustained increase in FABP.

Fetal growth restriction: adaptations and consequences

“…Intrafetal infusion of either cortisol or the synthetic glucocorticoids betamethasone and dexamethasone for periods of up to 48 h at about days 120-130 of gestation results in an increase in fetal femoral vascular resistance (Derks et al, 1997) and in arterial blood pressure (Wood et al, 1987;Tangalakis et al, 1992;Anwar et al, 1999). Infusion of cortisol for 6 days after bilateral fetal adrenalectomy also restored fetal arterial blood pressure to values measured in intact fetuses at about day 125 of gestation (Unno et al, 1999). Furthermore, blood pressure responses to increasing doses of angiotensin II, but not noradrenaline, were increased in sheep fetuses after infusion of cortisol for 48 h at about day 125 of gestation (Tangalakis et al, 1992).…”

Periconceptional nutrition programs development of the cardiovascular system in the fetal sheep

“…There was no effect of either periconceptional or gestational undernutrition on fetal heart rate or on the decrease in fetal heart rate that occurs with increasing gestational age (16,37). The rpp (rpp ϭ systolic BP ϫ heart rate) has been used as a marker of myocardial oxygen consumption and thus of cardiac work in the sheep fetus (14) and human adult (15,29).…”

The role of the neural sympathetic and parasympathetic systems in diurnal and sleep state-related cardiovascular rhythms in the late-gestation ovine fetus

“…fetal heart rate variability; diurnal rhythm; fetal sheep; sleep state; autonomic nervous system DESPITE THE COMMON USE OF heart rate (HR) and HR variability (HRV) for fetal surveillance, the underlying efferent mechanisms controlling these rhythms remain incompletely understood (29). Diurnal rhythms in fetal HR and HRV are well established in late gestation in the fetal human (44), nonhuman primates (39), and sheep (3,4,9,11,42). These circadian rhythms are thought to be entrained by maternal signals (28) and coordinated, in part, by signals from a fetal "biological clock" in the suprachiasmatic nucleus (SCN) (5,26,41), although other fetal tissues may be involved (37).…”

“…Diurnal rhythms in fetal HR and HRV are well established in late gestation in the fetal human (44), nonhuman primates (39), and sheep (3,4,9,11,42). These circadian rhythms are thought to be entrained by maternal signals (28) and coordinated, in part, by signals from a fetal "biological clock" in the suprachiasmatic nucleus (SCN) (5,26,41), although other fetal tissues may be involved (37).…”