Notes: 1. In chronically cannulated ovine fetuses (100–130 days of gestation) the infusion of cortisol (86.7 ± 15 μg/h for 4 h) or human atrial natriuretic factor (ANF; 4.4 μg for 2 h) resulted in highly significant increases in the excretion of sodium, chloride, potassium and water.2. Cortisol had no significant effect on fetal plasma ANF concentrations. All values are mean and s.e.m. Plasma immunoreactive ANF was 53 ± 5 and 67.3 ± 13 pmol/L in the 4 h saline infused fetuses, and 51.3 ± 14.3 and 74 ± 13.3 pmol/L in cortisol-infused fetuses (n= 7). A separate group of fetuses received 2 h infusions of saline or hANF (4.4 ug/h), and plasma IR-ANF values were measured (n= 3). The values, at 0, 60, 90 and 120 min were, respectively, 19.7 ± 3, 17.3 ± 0.7, 18.7 ± 3.7 and 20.7 ± 3.7 pmol/L in the saline infused group, and 25.3 ± 5.3, 80.7 ± 32.3, 123.3 ± 4.3 and 100 ± 15 pmol/L in the ANF-infused fetuses.3. Blood cortisol concentrations, in fetuses infused for 4 h with 0.9% NaCl, were 3.1 ± 0.8 nmol/L (n= 7); in fetuses infused with 0.9% NaCl for 2 h were 3.6 ± 1 nmol/L (n= 3); in fetuses infused for 4 h with cortisol were 19.9 ± 1.9 nmol/L (n= 7); and in fetuses infused with hANF for 2 h were 6.0 ± 3.0 nmol/L (n= 5).4. There was no effect of fetal hANF infusion on maternal or fetal blood aldosterone concentrations.5. The conclusion of this study was that cortisol and ANF cause natriuresis and diuresis in the immature ovine kidneys by independent mechanisms.

Notes: 1. The earliest form of the kidney, the pronephros, does not really occur in the ovine embryo; instead, a giant glomerulus forms at the anterior end of the mesonephros.2. In the sheep, the mesonephros is present from 11-38% of total gestation (150 days) and produces a dilute urine, as well as expressing the genes for erythropoietin, renin, angioten-sinogen, angiotensin-converting enzyme and the angiotensin II (AngII) receptors AT1 and AT2.3. The ovine metanephros begins to develop at 18% of gestation and nephrogenesis is complete several weeks before birth. AH components of the renin-angiotensin system (RAS) are expressed from at least 27% of gestation.4. Both AT1 and AT2 receptors are expressed by the adrenocortical cells early in gestation but, at mid-gestation, exogenous AngII does not stimulate aldosterone secretion in vivo.5. Preliminary results suggest that Angll has important roles in renal development in the ovine foetus but the role(s), if any, in adrenal development, remains to be investigated.

Notes: 1. Blood volume was measured weekly using [51Cr]-labelled red cells in 10 lambs from 3 to 10 weeks of age. Red cell and plasma volumes were calculated using the measured blood volume and haematocrit. Other parameters, including plasma erythropoietin, urea, creatinine and glucose, were measured twice weekly. The results were compared to a group of five lambs that received an infusion of insulin-like growth factor I (IGF-I).2. In control lambs, plasma volume increased linearly by 47 ± 7 mL/week over the experimental period. Red cell volume only increased by 10 ± 2 mL/week during weeks 3–7, but then increased by 25 ± 2 mL/week over weeks 7–10. Haematocrit declined from 28.0 ± 1.6 to 24.7 ± 1.7% over weeks 3–7 and then increased to 30.7 ± 1.1% by week 10.3. In 10 control lambs infused for 8 days (starting at 22–26 days of age) with 10 mmol/L HCl, there was a decrease in plasma IGF-I concentrations, 3 days after the start of infusion. In five lambs infused for 8 days with IGF-I (6 μg/kg per h) plasma IGF-I concentration was maintained significantly (P 〈 0.01) higher than that of the controls.4. There was no significant difference in haematocrit, red cell or plasma volumes between the treatment groups and no reticulocytosis was observed. Plasma erythropoietin concentrations did not change over the infusion period in either group.5. Serum urea decreased significantly in the IGF-I infused group but serum creatinine did not change in either group during the infusion period. In both the groups, there was a significant decrease in glucose, urea and creatinine over weeks 3–10 after birth. There was no difference in growth rates between the two groups.6. Thus, it appears that the observed changes in haematocrit are due to a constant increase in plasma volume with varying rates of red cell volume increases.7. IGF-I infused at a dose that maintains physiological concentrations and alters protein metabolism does not result in increased erythropoietin or erythropoiesis during the neonatal period of the lamb.

Notes: 1. The reproducibility of blood volume measurements, using [51Cr]-labelled red blood cells (RBC) was tested in three lambs, 79–89 days of age, and the accuracy was tested in eight lambs, 83± 0.4 days of age, in which blood volume was measured simultaneously by [51Cr]-RBC and [125I]-gamma globulin plus haematocrit (hct).2. The blood volumes (mean ± s.e.) of the three lambs, on four occasions, were 64.5± 2.5, 68.8 ± 2.9 and 63.9 ± 3.7 mL/kg, respectively, and the coefficients of variation were 7.8, 8.6 and 11.6%, respectively.3. The mean blood volume of eight lambs was 60.9 ± 3.3 mL/kg by [51Cr]-RBC, and 60.8 ± 2.4 mL/ kg from plasma volume and hct. These were not statistically different.4. Arterial hct was 31.2 ± 0.5%, which was not statistically different from the whole body hct of 31.2 ±2.6%.5. It is concluded that [51Cr]-RBC can be used to measure accurate and reproducible blood volumes in lambs.

Notes: 1. The effects of intravenous infusions of arginine vasopressin (AVP), parathyroid hormone-related protein (PTHrP) and AVP + PTHrP on renal function in intact ovine foetuses at 100–125 days of gestation were examined.2. A low dose of AVP (5.5 ± 0.9 pmol/h) increased plasma AVP concentrations from 0.6 pmol/L to 2.1 ± 0.4 pmol/L (mean ± s.e.m; n= 8). This dose caused a significant reduction in free water clearance (CH2O; P〈0.001), without any significant change in fetal arterial blood pressure, glomerular filtration rate (GFR), or the urinary excretion rates of sodium, calcium or 3', 5'-cyclic adenosine monophosphate (CAMP).3. Infusions of PTHrP (1 nmol/h), with or without 1 nmol bolus dose, significantly increased (P〈0.05) urine osmolality (Uosm), but did not synergize with AVP in reducing CH2O.4. It is concluded that AVP and PTHrP do not act synergistically on the kidney of the intact ovine foetus.

Notes: 1. This study describes the effects of prolonged (48 h) infusion of cortisol into ovine foetuses (100–110 days of gestation: term is 150 days) at a time when endogenous plasma cortisol concentrations are 〈5 nmol/L.2. In four chronically cannulated foetuses (107 ± 0.9 day) the infusion of saline (0.9% NaCl; w: v 0.19 mL/h, 48 h) had no effect on blood pressure, renal function, or composition of amniotic and allantoic fluids.3. In six foetuses (107 ± 1 day) the infusion of cortisol (250 μg/h) increased plasma cortisol concentrations from 4.1 ± 0.7 to 118 ± 9 nmol/L (P 〈 0.001), increased mean arterial pressure from 34 ± 1 to 40 ± 1 mmHg (P 〈 0.001), increased glomerular filtration rate (P〈0.05), urine flow rate, and free water clearance (P〈0.01).4. There was a significant increase in excretion rates of potassium and creatinine as a result of cortisol infusion, but no natriuresis, indicating some functional maturation of the fetal kidney.5. Cortisol infusion had no effect on the volumes of amniotic and allantoic fluids; allantoic fluid composition was unchanged; significant decreases occurred in amniotic fluid osmolality, sodium and chloride concentrations, and in lung liquid osmolality, potassium, creatinine, magnesium, glucose and fructose concentrations.6. Thus prolonged exposure of the immature ovine foetus to elevated cortisol concentrations produced significant alterations in the water and electrolyte balance of the foetus.

Notes: SUMMARY 1. The concentrations of aldosterone, corticosterone, cortisol and renin substrate in plasma and the plasma renin activity were determined in five non-pregnant and five pregnant rhesus monkeys.2. The mean aldosterone concentrations are 25.9 ng/100 ml in the non-pregnant and 31.4 ng/100 ml in the pregnant monkey: the difference is not significant (P〉0.5).3. The mean corticosterone concentrations are 1.11 and 1.84 μg/100 ml respectively: the difference is not significant (P〉0.1).4. The mean cortisol concentrations are 21.3 and 28.2 μg/100 ml respectively: the difference is significant (P〈0.05).5. Pregnancy does not result in increases in either plasma renin activity, mean values being 4.96 and 3.72 ng/ml per h, respectively, or renin substrate concentrations, the means being 1.09 and 0.82 μg/ml, respectively.6. The lack of elevation of these hormones is consistent with findings that concentrations of progesterone and oestrogen are only slightly increased in pregnancy in rhesus monkeys.

Notes: 1. In conscious ewes pregnancy was associated with a significantly increased heart rate and cardiac output, while mean arterial pressure (MAP) and stroke volume were unchanged.2. The present study examines the effect of arginine vasopressin (AVP) infused at 0.3, 1, 3.0, and 10 μg/h, into water-loaded and sodium-depleted ewes, either non-pregnant or during the last third of gestation.3. In the water-loaded state, MAP rose significantly at the lowest rate of infusion in both pregnant and non-pregnant ewes. Bradycardia occurred first at 0.3 μg/h in the pregnant ewes but not until 3.0 μg/h in the non-pregnant animals.4. In sodium deficiency there was no increase in MAP at any rate of infusion in either group. Bradycardia occurred in both groups at 1 μg/h.5. This study shows that the pressor effects of AVP are unchanged by pregnancy. However, pregnant ewes are more sensitive to AVP-induced bradycardia when the ewes are water-loaded.

Notes: 1. The peripheral blood concentrations of aldosterone, corticosterone and cortisol were measured during pregnancy in conscious, undisturbed sheep.2. Aldosterone levels did not change during pregnancy and the mean pregnant value, 1·2 s.d. 1·4 ng/100 ml (n= 12) was not significantly different from the non-pregnant value, 2·1 s.d. 1·7 (n= 16).3. Cortisol levels likewise were unchanged by pregnancy–non-pregnant values were 0·56 s.d. 0·50 μg/100 mi (n= 12) compared with 0·46 s.d. 0·40 μg/100 ml (n= 16) in pregnant sheep.4. Sheep of 110–140 days gestation had a 400 mmol greater total exchangeable sodium than non-pregnant sheep. Plasma volume and plasma renin concentration tended to be elevated near to term.5. Very high aldosterone secretion rates and peripheral blood levels could be produced in pregnant sheep by stress, intravenous ACTH or angiotensin II infusions, and by sodium deficiency. It is suggested that the pregnant sheep may show increased sensitivity in contrast to non-pregnant sheep to these stimuli and the enlarged size of their adrenals may be a contributing factor.

Notes: 1. It now appears that when water crosses an endothelium which is not fenestrated, or an epithelium with tight junctions, it does so rapidly, and with low energy cost, only if the cell membrane contains an adequate number of specific water channels, encoded by one of at least six different genes.2. The water channel genes so far cloned encode a series of integral membrane proteins called aquaporins, all of approximately 30kDa (265–282 amino acids), in the unglycosylated state. All but one (AQP3) are specific water channels and all but one (AQP4) are inactivated by mercurial compounds.3. Aquaporin 0 is the major (60%) intrinsic protein (MIP) of lens fibre cells of the eye. Mutations in this gene are associated with cataract formation in mice.4. Aquaporin 1, also called CHIP-28, exists in the membrane as a homotetramer, and is present in red blood cells, the choroid plexus, the proximal tubule and descending limb of the loop of Henle in the kidney as well as in many other sites. Surprisingly, no pathological consequence is known in patients lacking a functional AQP1 gene.5. Aquaporin 2, also called WCH-CD, is the water channel of the principal cell of the cortical and medullary collecting duct, and is located in cytoplasmic vesicles unless arginine vasopressin is acting, when it is translocated to the apical membrane by synaptobrevins or vesicle associated membrane protein 2 (VAMP2). Lack of a functional AQP2 gene leads to a rare form of nephrogenic diabetes insipidus.6. Aquaporins 3, 4, and 5 are located in many tissues—AQP3 and AQP4 being in the basolateral membrane of the renal cortical and medullary principal cell, as well as in the gastrointestinal tract (AQP3) and the brain (AQP4).7. Four sequences are known for urea transporters HUT11—the urea transporter of the human red cell membrane, and HUT2, rUT2, rbUT2—the arginine vasopressin inducible urea transporters of the human, rat and rabbit kidney. They are specifically permeable to urea, not to water, and are claimed to be inhibited by phloretin.8. The water channel proteins contain six membrane-spanning regions, whilst the urea transporters are thought to contain at least 10 membrane spanning segments.9. Very little work has examined the ontogeny of these proteins, except in the rat, and virtually nothing is known of the expression of these genes in pregnancy or in any disorder of fluid balance in the mother or foetus.