Marian Silver

The composition of foetal and maternal blood during parturition in the ewe

1. Changes in the composition of foetal and maternal blood have been followed during the last 5–10 days of gestation and throughout parturition in the conscious sheep.

The Prenatal Development and Glucocorticoid Control of Brush-Border Hydrolases in the Pig Small Intestine

The development of brush-border enzymes and the possible regulatory role of cortisol were investigated in the small intestine of the fetal and neonatal pig. With the sows under pentobarbitone anesthesia, osmotic minipumps containing either saline or cortisol were inserted s.c. into 25 fetuses from 10 pregnant sows (82–96 d gestation). Six d later, the infused fetuses were removed by cesarean section and samples of the proximal, middle, and distal intestine taken for analysis. Samples were also obtained from 48 piglets that did not undergo an operation (controls) and that were removed at intervals from 82 d gestation until term (114 ± 2 d). In the proximal and middle intestine, the mean levels of lactase-phlorizin hydrolase (EC 3.2.1.23–62), maltase-glucoamylase (EC 3.2.1.20), aminopeptidase N (EC 3.4.11.2), and aminopeptidase A (EC 3.4.11.7) increased during the last 10–15 d before term, correlated positively with log10 plasma cortisol values, and were higher in cortisol-infused than in saline-infused fetuses (p < 0.05). Activity of sucrase-isomaltase (EC 3.2.1.48–10) was low in fetal pigs, and this enzyme and dipeptidyl peptidase IV (EC 3.4.14.5) were not significantly affected by fetal age or exogenous cortisol. Maltase (EC 3.2.1.48–10 and EC 3.2.1.20) activity was significantly decreased in the middle and distal intestine of cortisol-infused fetuses. The results suggest that the prepartum rise in endogenous cortisol secretion stimulates the prenatal expression of certain brush-border enzymes in the pig small intestine at this critical time. However, the effects of cortisol on the developing intestine were highly idiosyncratic for particular enzymes and intestinal regions.

The development of the adrenal medulla of the foetal and new-born calf

1. The output of adrenaline and noradrenaline from the adrenal medulla during asphyxia, stimulation of the splanchnic nerves or the intra‐arterial injection of acetylcholine, has been investigated in foetal and new‐born calves up to 3 weeks of age.

Developmental regulation of glucogenesis in the sheep fetus during late gestation

1 Using tracer methodology, endogenous glucose production was measured in twenty‐six chronically catheterized sheep fetuses during normal fed conditions and in response to a 48 h period of maternal fasting at different gestational ages during the last 10‐15 days of gestation (term, 145 ± 2 days). 2 In normal fed conditions, the rate of fetal glucose production was negligible until 143‐145 days when it rose significantly to account for 50 % of the glucose used by the fetus. The rise in fetal glucogenesis towards term closely parallelled the normal prepartum rise in fetal plasma cortisol and catecholamines. 3 Maternal fasting for 48 h induced endogenous glucose production in fetuses at 139‐141 days but not at 133‐135 days of gestation. Maternal fasting also induced increases in the plasma cortisol and noradrenaline levels in all the fetuses studied. Fetal plasma cortisol levels at the end of the fast and the increment in fetal plasma cortisol during maternal fasting were significantly greater in the older groups of fasted animals. 4 When the data from all the fetuses were combined, partial correlation analysis of fetal glucose production and the log plasma concentrations of cortisol and total catecholamines showed that plasma cortisol was the predominant regulator of fetal glucogenesis during late gestation. However, once plasma cortisol levels exceeded 17.5 ng ml−1, plasma catecholamines were a major influence on fetal glucogenesis. 5 The results show that glucogenesis occurs in fetal sheep during late gestation in conditions in which the fetal plasma concentrations of cortisol and catecholamines are elevated. They also suggest that cortisol enhances the capacity for glucogenesis in utero, while catecholamines actually activate glucose production in sheep fetuses close to term.

Cardiovascular and endocrine responses to feeding in the young calf.

A number of cardiovascular and endocrine responses which occur during and after feeding in the unweaned calf are described. 2. There was a substantial increase in both heart rate and mean aortic blood pressure during feeding in these animals. This occurred within the first few seconds and persisted throughout the period of ingestion. 3. The concentrations of glucose, insulin and gastrin in arterial plasma rose abruptly during, or immediately after, feeding and elevated values persisted for at least 2 hr. A transient increase in glucagon concentration was also observed. In contrast, feeding appeared to produce no immediate rise in enteroglucagon concentration. 4. The adrenal output of glucocorticoids rose transiently in response to feeding but that of catecholamines was unaffected. 5. Cardiovascular responses to feeding were also examined in other species. In unweaned kids the changes were essentially similar to those observed in the calf but were less pronounced. In lambs a persistent hypertension occurred which was associated with a brief initial tachycardia. In adult dogs ingestion of solid food also caused tachycardia but although the aortic blood pressure rose for a short period at the beginning of feeding, hypotension developed thereafter. 6. The possibility that both the cardiovascular and endocrine responses, which occur during or immediately after feeding, are mediated by the autonomic nervous system is discussed.

The glycogenolytic response to stimulation of the splanchnic nerves in adrenalectomized calves.

1. The effects of stimulation of the peripheral ends of one or both splanchnic nerves have been investigated in adrenalectomized calves at different ages.

Daily changes in foetal and maternal blood of conscious pregnant ewes, with catheters in umbilical and uterine vessels

1. Blood gas tensions, pH, packed cell volume (PCV) and the levels of glucose, fructose and lactic acid have been followed in foetal and maternal blood for periods of 3‐30 days in conscious ewes between 80 days gestation and term (∼ 147 days).

Comparison of the hyperglycaemic and glycogenolytic responses to catecholamines with those to stimulation of the hepatic sympathetic innervation in the dog

1. The effects of stimulation of the splanchnic innervation to the adrenal medullae, in dogs with cut hepatic nerves, were compared with those obtained previously in response to splanchnic and hepatic nerve stimulation in adrenalectomized dogs.

Prostaglandins in the foetal pig and prepartum endocrine changes in mother and foetus

Abstract Chronically catheterized sows and their foetuses were used to investigate the changes in steroids and prostaglandins in maternal and foetal plasma and in allantoic fluid before and during parturition. A rise in foetal plasma corticosteroid concentration began 5–7 days before delivery. This was accompanied by a rise in oestrogen levels in foetal and maternal plasma and in allantoic fluid. There were significant venous-arterial differences in oestrogen across both uterine and umbilical circulations. A more gradual decrease in maternal plasma progesterone levels occurred with a pronounced fall 24 hr before parturition; wide arterio-venous (uterine) and venous-arterial (umbilical) progesterone differences were found. Prostaglandin concentrations remained low in the maternal circulation until the day of farrowing, when PGF and its metabolite 13,14-dihydro-15-oxo prostaglandin (PGFM) rose 10–20 fold. Foetal plasma levels of PGE, PGF and PGFM were higher than those of the sow in the prepartum period, while allantoic fluid concentrations were even greater. At delivery, PGE and PGF in the umbilical vein and allantoic fluid were raised but in the arterial plasma of the piglets at birth only PGFM levels were high. There was a close correlation between the neonatal PGFM levels and those in maternal arterial plasma at the time of delivery.

PO2, PCO2 and pH levels in the umbilical and uterine blood of the mare and ewe

1. Foetal and maternal blood gas tensions and pH levels have been investigated in the mare and the ewe during late pregnancy under a number of experimental conditions.