D.P. Alexander

Maternal and Fetal Arginine Vasopressin in the Chronically Catheterised Sheep

Catheters were implanted into the fetal dorsalis pedis and maternal jugular veins of 6 ewes of 122–130 days gestation age. Fetal plasma arginine vasopressin (AVP) concentrations rose in the last few days before parturition from undetectable levels to values associated with response to minor stress. Similarly, AVP was frequently present in maternal plasma in the last week of gestation but was rarely detected earlier. The levels attained in the mother were somewhat lower than in the fetus.

Nitrogen Metabolism in the Sheep Fetus

Ammonium ions added in large quantity disappear rapidly from the reservoir of the sheep placenta perfused in situ through the umbilical vessels. Ammonium ions are removed from the reservoir of perfused sheep fetal livers of 108-141 days of conceptual age at a rate of at least 1 mumol/min/g liver. The majority appears as urea. There is little or no change in glutamine concentration. Hepatic carbamoylphosphate synthetase I, ornithine transcarbamylase, argininosuccinate synthetase, argininosuccinase and arginase are present, even at 97 days of conceptual age, in adequate amounts to account for the observed urea production. With the exception of arginase, all levels rise with fetal age. The levels in the maternal liver are comparable with those at 106 days of conceptual age. Arginase is high in the younger fetuses, falls progressively with fetal age and is very low in the mother. It is concluded that (a) the perfused placenta is permeable to ammonia and the placenta may be able to clear ammonia from the fetal circulation at a rate comparable with that of fetal liver; (b) the fetal liver converts ammonia to urea at a rate comparable with the urea production of the fetus; (c) there is virtually no glutamine production by the fetal liver; (d) adequate amounts of the enzymes of urea synthesis are present even in the immature fetal liver to account for the total urea production of the fetus, and (e) the anomalously low arginase level in the maternal liver may conserve maternal arginine, and the high levels in the younger fetuses may be related to fetal polyamine production from maternally derived arginine.

Maintenance of sheep fetuses by an extracorporeal circuit for periods up to 24 hours

Abstract The results obtained on two sheep fetuses maintained for 24 hours on an artificial perfusion circuit (artificial placenta) with the umbilical vessels are described. The problems involved in the maintenance of such isolated fetuses for prolonged periods on extracorporeal circuits are discussed.

Antidiuretic Hormone and Oxytocin Release and Antidiuretic Hormone Turnover in the Fetus, Lamb and Ewe

The release of antidiuretic hormone in response to the introduction of an osmotic stimulus into the cerebral circulation of the fetal sheep and lamb is described. Infusion of 1.0 M

Glucagon Release in the Sheep Fetus

Arginine administered to the fetal sheep elicits a brisk transient increase in the glucagon concentration of peripheral fetal plasma. Neither direct elevation of the fetal plasma glucose level nor the

Corticotrophin and cortisol concentrations in the plasma of the chronically catheterised sheep fetus.

Plasma from six chronically catheterised sheep fetuses of 113–126 days conceptual age showed high levels of corticotrophin at all ages with somewhat higher values towards term. Plasma cortisol was not clearly related to corticotrophin in individual samples but was highly correlated in the pooled data. Short bouts of hypoxia (5–10 min 10% O2 in N2 to the mother) produced no significant change in either corticotrophin or cortisol although small transient changes in PO2 and lactate occurred. The high levels of corticotrophin suggest that the possibility of stress in the chronically catheterised preparation must be considered.

Localization of Tamm-Horsfall Glycoprotein in the Fetal and Neonatal Hamster Kidney as Demonstrated by Immunofluorescence and Immunoelectron Microscopical Techniques

Tamm-Horsfall (T-H) glycoprotein was demonstrated in the developing hamster kidney using immunofluorescence and immunoelectron microscopical techniques. The glycoprotein was first observed in the fetal kidneys on the 12th day of gestation and was confined to the luminal surface of the presumed distal tubules of the medulla. It was not until the 14th day of gestation that T-H glycoprotein was also sometimes seen to be associated with the lateral and basal invaginations of the plasma membranes of the now differentiated distal tubules. On the 16th day (1st day post-partum) the glycoprotein was also found in the cortex. Although the general distribution of T-H glycoprotein was at 3-4 days after birth similar to the adult, the full intensity of staining was not attained until after the 21st day. The possible physiological significance of these findings is discussed.

Insulin Secretion in the Fetal and Neonatal Sheep

The effect on plasma insulin of elevating plasma glucose levels was studied in exteriorized sheep fetuses of 68 to 142 days conceptual age and in 2 lambs, 1 and 7 days old. Fetuses of less than 110 da

Prolactin in the Sheep Fetus: Effect of Reserpine

The presence of prolactin, in quantities comparable with the adult, has been confirmed in the plasma of the fetal sheep a few days before term (140 and 144 days) but at 101 and 105 days only traces we