Developmental regulation of preproenkephalin (PENK) gene expression in the adrenal gland of the ovine fetus and newborn lamb: effects of hypoxemia and exogenous cortisol infusion

Effect of cortisol on C-type natriuretic peptide in ovine pregnancy: differential responses in fetal and placental tissues

We have used aminoterminal pro C-type natriuretic peptide (NTproCNP)--a stable marker of CNP secretion--to study the effect of cortisol on CNP secretion and fetal growth. In ovine pregnancy, maternal plasma NTproCNP (largely sourced from the placenta) increases at the end of the first trimester and then decreases abruptly preterm during the phase of fetal surge in cortisol secretion. Postulating that increases in cortisol, as occurs in the fetal or maternal circulation in late pregnancy, will reduce CNP secretion, we studied the fetal and maternal responses in NTproCNP to sustained low-dose infusions of cortisol (1.2 mg/d/kg for 11 d) delivered to the fetus from d 117 gestation. Fetal plasma NTproCNP was progressively reduced during fetal cortisol infusions, whereas fetal girth growth was unchanged. In contrast, maternal NTproCNP was unaffected by cortisol. We conclude that fetal but not placental tissue production of CNP is reduced by small increments in fetal cortisol. Failure to reduce maternal NTproCNP may relate to the continuing presence of the placental barrier to cortisol at this stage of pregnancy.

Effect of cerebral hypothermia on cortisol and adrenocorticotropic hormone responses after umbilical cord occlusion in preterm fetal sheep

The hypothalamic-pituitary-adrenal (HPA) axis is essential for adaptation to stress. In the present study, we examined the hypothesis that head cooling with mild systemic hypothermia would adversely affect fetal adrenocorticotropic hormone (ACTH) and cortisol responses to an asphyxial insult. Chronically instrumented preterm fetal sheep (104 d of gestation, term is 147 d) were allocated to sham occlusion (n = 7), 25 min of complete umbilical cord occlusion (n = 7), or occlusion and head cooling with mild systemic hypothermia (n = 7, mean +/- SEM esophageal temperature 37.6 +/- 0.3 degrees C vs 39.0 +/- 0.2 degrees C; p < 0.05) from 90 min to 70 h after occlusion, followed by spontaneous rewarming. During umbilical cord occlusion, there was a rapid rise in ACTH and cortisol levels, with further increases after release of cord occlusion. ACTH levels returned to sham control values after 10 h in both occlusion groups. In contrast, plasma cortisol levels remained elevated after 48 h in both occlusion groups and were still significantly elevated in the hypothermia-occlusion group 2 h after rewarming, at 72 h, compared with the normothermia-occlusion and sham groups. In conclusion, hypothermia does not affect the overall HPA responses to severe asphyxia in the preterm fetus but does prolong the cortisol response.

Cortisol and ACTH responses to severe asphyxia in preterm fetal sheep

It has been hypothesized that the hypothalamic-pituitary-adrenal (HPA) axis is immature in the preterm fetus and that this compromises their ability to adapt to hypoxic stress; however, there are few direct data. We therefore examined the effects of asphyxia on HPA responses in chronically instrumented preterm fetal sheep (104 days of gestation; term is 147 days), allocated to a sham control group (n = 7) or 25 min of complete umbilical cord occlusion (n = 8), followed by recovery for 72 h. During umbilical cord occlusion there was a rapid rise in ACTH levels (230.4 +/- 63.5 versus 14.1 +/- 1.8 ng ml(-1) in sham controls, 16-fold) and cortisol levels (7.4 +/- 4.9 versus 0.2 +/- 0.1 ng ml(-1), 31-fold), with further increases after release of cord occlusion. ACTH levels were normalized by 24 h, while plasma cortisol levels returned to sham control values 72 h after asphyxia. Fetal arterial blood pressure was elevated in the first 36 h, with a marked increase in femoral vascular resistance, and correlated positively with cortisol levels after asphyxia (P = 0.05). In conclusion, the preterm fetus shows a brisk, substantial HPA response to severe hypoxia.

Cardiovascular and endocrine effects of a single course of maternal dexamethasone treatment in preterm fetal sheep

OBJECTIVE

To determine the effects of a single course of maternally administered dexamethasone on preterm fetal sheep in utero.

DESIGN

Prospective randomised controlled trial.

SETTING

University laboratory.

SAMPLE

Pregnant sheep at 0.7 of gestation.

METHODS

Pregnant ewes at 103 days of pregnancy (term = 147 days) were given two intramuscular injections of vehicle (n= 7) or 12 mg of dexamethasone (DEX; n= 8) 24 hours apart. Fetuses were continuously monitored for five days.

MAIN OUTCOME MEASURES

Fetal mean arterial blood pressure, carotid and femoral arterial blood flow and vascular resistance, heart rate, heart rate variability, fetal plasma cortisol and ACTH and fetal body movements.

RESULTS

DEX injections led to an acute increase in mean arterial blood pressure with a rise in carotid and femoral vascular resistance, a fall in femoral arterial blood flow, and a brief fall in fetal heart rate followed by significant tachycardia. From 24 hours after the injections, mean arterial blood pressure and vascular resistance returned to control values, however, a mild tachycardia [200 (3) vs 184 (4) bpm, P < 0.05] and loss of the circadian pattern of fetal heart rate variability persisted until the end of recording. Plasma ACTH and cortisol were markedly suppressed by DEX (P < 0.05), with values returning to control levels 32 and 72 hours after the first injection, respectively. There was no effect on basal fetal heart rate variability, body movements, carotid arterial blood flow, or the circadian pattern of fetal heart rate.

CONCLUSION

In contrast to previous experiments utilising direct fetal infusion of steroids, maternal administration of DEX was associated with only transient hypertension.

Fetal hypoxemia on a molecular level: adaptive changes in the hypothalamic-pituitary-adrenal (HPA) axis and the lungs

The development of diseases in later life, such as diabetes type II, hypertension and cardiovascular disease, is linked to abnormal intrauterine conditions that reduce birth weight. Obviously, fetal development can be disturbed so profoundly, that fetal programming is changed permanently. We have examined the effects of hypoxia, or more precisely hypoxemia, on the fetal hypothalamic-pituitary-adrenal (HPA) axis and lungs using molecular biology techniques in order to elucidate the underlying mechanisms. Chronically catheterized fetal sheep were subjected to a hypoxemia (48 h) without change in arterial pH or paCO2. Major changes occurred, although the degree of hypoxemia was just moderate. There was a transient increase in the fetal plasma ACTH-concentrations with an upregulation of the cortisol-concentrations, which was more pronounced in the older, hypoxemic fetuses (134-136 days of gestation) than in the younger, hypoxemic animals (126-130 days of gestation; term is 145 days). There was an unique, differential regulation for pro-opiomelanocortin messenger RNA (mRNA), the precursor molecule of e.g. ACTH, in the pars distalis and pars intermedia of the pituitary gland. This finding supported the increased bioactivity besides the increased concentrations for ACTH. Simultaneously, there was an increase in the mRNAs of the ACTH-receptor and of the steroid-synthesizing enzymes in the fetal adrenal gland of the older, hypoxemic fetuses. No changes in the fetal plasma androstenedione-concentrations were observed. Clearly, there was a selective increase of the cortisol-synthesis. Growth and maturation of the fetal lung might also have been affected, because of the increase in surfactant-protein A mRNA in the older, hypoxemic animals and the decrease in the insulin-like growth factor-I and its binding protein-5 mRNA in the younger, hypoxemic fetuses. In summary, even a moderate degree of hypoxemia was shown to affect the different levels of fetal organism profoundly, offering a pathophysiological basis for changes in fetal development.

Endogenous opiates: 1997

This paper is the twentieth installment of our annual review of research concerning the opiate system. It summarizes papers published during 1997 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; eating and drinking; alcohol; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunologic responses; and other behaviors.