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. 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. Fetal exposure to an adverse intrauterine environment has been linked with cardiovascular and metabolic disease later in life. We have shown previously, in sheep, that brief exposure (48 h) to maternally administered dexamethasone (0.28 mg/kg per day) at 27 days of gestation (prenatal treatment group (PTG) 1; term approximately 150 days), but not at 64 days of gestation (PTG2), produced hypertensive offspring at 40 months of age. The present study aimed to determine whether the elevated blood pressure in these sheep was associated with an altered peripheral renin–angiotensin system (RAS).2. Measurements of the basal levels of the RAS components (renin, angiotensinogen, angiotensin (Ang) I, angiotensin- converting enzyme (ACE), AngII and Ang-(1–7)) were made. In addition, we studied the effect of a peripherally administered AngII type 1 (AT1) receptor antagonist (irbesartan at 1.02 mg/kg per h) on mean arterial pressure (MAP) over 4.5 h.3. There was no significant difference in basal plasma concentrations of the components of the RAS measured between control (n = 7) and PTG1 (n = 5) or PTG2 (n = 6) animals. The MAP in PTG1 was significantly higher than in the control group during both vehicle infusion and AT1 receptor blockade. The effect of 4.5 h irbesartan (1.02 mg/kg per h) infusion on blood pressure was similar between the groups.4. In conclusion, intrauterine exposure for 48 h to maternally administered dexamethasone at 27 days of gestation caused elevated blood pressure in adult sheep that does not appear to be associated with an alteration in the peripheral RAS.

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. 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: 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. When pregnant ewes and their fetuses are exposed to the synthetic glucocorticoid dexamethasone for 2 days early in pregnancy (days 26–28; term 145–150 days), female offspring have increased blood pressure relative to a control group. In one series, this was shown to be due to increased cardiac output, concomitant with a reset mean arterial pressure/heart rate reflex. The first group of such animals had, by the age of 7 years, left ventricular hypertrophy and reduced cardiac functional capacity.2. The elevation in blood pressure is not maintained by any change in the peripheral renin–angiotensin system (RAS).3. There is, however, preliminary evidence that some aspects of local RAS (particularly in the kidney and brain) could have participated in the ‘programming’ event. The levels of mRNA for angiotensin II receptors (AT1, AT2) and angiotensinogen are increased in the kidney of such dexamethasone-treated fetuses in late gestation (130 days), some 100 days after steroid treatment. Similar increases in AT1 mRNA in the medulla oblongata of the fetal brain and large increases of mRNA for angiotensinogen occur in the hypothalamus.4. These findings, together with evidence from the literature, suggest that both the kidney and parts of the brain are affected by events that also ‘program’ high blood pressure in the offspring of animals in which the intra-uterine environment has been perturbed at some stage.

Notes: 1. The role of the kidneys in the maintenance of normal foetal plasma (FP) composition and hormone concentrations was examined in the present study. Five ovine foetuses were chronically cannulated and nephrectomized (nephx) at 100±1 days of gestation and maintained for 14 days. These were compared to five intact control foetuses.2. Four hours after nephx, FP renin concentrations were significantly lower than in control foetuses. By 48 h, renin concentrations in nephx foetuses were below the level of detectability of the assay. Foetal plasma aldosterone concentrations declined in nephx foetuses, but were not significantly different to those in control foetuses (P = 0.08).3. During the second week, the nephx foetuses were significantly hypoxic, but FP erythropoietin concentrations were not increased. Adrenocorticotropic hormone (ACTH) and cortisol concentrations, when measured on day 14, were not different between the two groups. Adrenocorticotropic hormone levels were correlated with adrenal weight at post-mortem.4. Foetal plasma creatinine, magnesium and phosphate concentrations in nephx foetuses increased, eventually reaching values approximately twice that in controls. Foetal plasma chloride levels decreased continuously in nephx foetuses, eventually being 23 mmol/L lower than controls. Maternal plasma composition was unchanged.5. Total foetal fluid (amniotic + allantoic) volumes were reduced when measured at post-mortem on day 14 after nephx. The composition of both fluids was significantly altered in the nephx foetuses compared with controls.6. Fetuses can survive in utero for 2 weeks after bilateral nephrectomy. However, there are multiple changes in plasma composition that may compromise foetal survival in the long term.

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. 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.