Maternotoxicity and fetotoxicity of an angiotensin-converting enzyme inhibitor, enalapril, in rabbits

Is omphalocele a non-specific malformation in New Zealand White rabbits?

We evaluated the incidence of omphalocele, a malformation that occurs sporadically in many studies. We assembled data on external malformations using all treatment groups from every study published in three major journals over the past 35 years using New Zealand White rabbits. Fifty-eight papers were included: 4905 litters and 36,977 fetuses. Omphalocele was reported in 43% and was among the most common defects, occurring at a rate of 1.10% (litter) and 0.16% (fetus). The defect did not appear to be treatment-related, although it may have been in two studies, based on rate and dose-responsiveness. Removing these two studies from the analysis, the defect was still prevalent (0.77% litter, 0.11% fetal incidence). Three studies evaluated the effects of food restriction and omphalocele was observed with food restriction in two of them, suggesting that decreased maternal weight gain or food consumption may be causal. Otherwise, it appears to be spontaneous and common.

Is there an embryopathy associated with first-trimester exposure to angiotensin-converting enzyme inhibitors and angiotensin receptor antagonists? A critical review of the evidence

Drugs that interfere with the renin-angiotensin system, such as angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs), are widely used to manage hypertension and heart failure. Adequate functioning of the RAS is essential for normal fetal kidney development. The potential for ACEIs and ARBs to impair fetal and neonatal renal function if taken after the first trimester of pregnancy has been well documented. Although these drugs were not found to be teratogenic in animals, until recently little was known about the teratogenic effects of ACEIs and ARBs in humans when exposure was limited to the first trimester of pregnancy. New evidence from epidemiologic studies indicates that there may be an elevated teratogenic risk when these drugs are taken during the first trimester of pregnancy. However, this elevated risk does not appear to be specific to ACEIs and ARBs, but is instead related to maternal factors and diseases that typically coexist with hypertension in pregnancy, such as diabetes, advanced maternal age, and obesity. Women who become pregnant while being treated with an ACEI or ARB should be advised to avoid exposure to these drugs during the second and third trimesters of pregnancy by switching to a different class of antihypertensive drugs between weeks 8 and 10 after conception.

Effects of stage and degree of restricted feeding on pregnancy outcome in rabbits

This study's aim is to investigate the relationship between stage and degree of restricted feeding during the gestation period and occurrence of abortion, premature birth or fetal damage in rabbits. The study was composed of 5 groups of pregnant Kbl:NZW rabbits that consisted of 8 animals each. These groups were subjected to restricted feeding in the following ways: (A) control group, free access to food, (B) 60 g per day from gestational days (GD) 6 to 18 (middle period), (C) 20 g per day from GD 6 to 18, (D) 20 g per day from GD 19 to 28 (post-middle period), and (E) 20 g per day from GD 6 to 28 (middle and post-middle periods). Even though all dams in Groups A, B and C went to full term, abortion or premature birth occurred to 2/8 and 8/8 dams in Groups D and E, respectively. Fetal lethality increased in Group C, which was subjected to restricted feeding at 20 g/head/day in the middle period. Slight inhibition of fetal growth was recorded only in Group D, which was subjected to restricted feeding in the post-middle period. Restricted feeding at 20 g/head/day in the middle period induced no abortion or premature birth, but increased fetal lethality that in the middle and post-middle periods resulted in abortion or premature birth of all dams, and that in the post-middle period resulted in abortion or premature birth at low incidence and slightly inhibited fetal growth. These results demonstrated that the post-middle period is vulnerable to effects of reduced food consumption in pregnant rabbits.

Mode of action: angiotensin-converting enzyme inhibition--developmental effects associated with exposure to ACE inhibitors

Relative to species tested in laboratory studies, the human fetus displays higher vulnerability to enalapril and other angiotensin-converting enzyme inhibitors (ACEI) exhibiting a malformative syndrome that does not appear to have a similar counterpart in experimental animals. An important reason for this higher vulnerability is the earlier intrauterine development of the kidney and the renin-angiotensin-aldosterone (RAS) system in humans, organ systems that are specific targets of ACEI's pharmacological effect. In humans, these systems begin developing prior to the onset of skeletal ossification at the end of the first trimester, with continuing vulnerability throughout the pregnancy. In most animal species tested, these target systems develop close to term, when the fetus is relatively more mature and less vulnerable to the effects of developmental toxicants. For this reason, animal studies that follow standard protocols and evaluate developmental toxicity only for exposures during embryogenesis will miss developmental effects arising secondary to disruption of target systems that develop after the period of major organogenesis. Thus, although the animal mode of action (MOA) for enalapril and other ACEI is plausible in humans, differences in the timing of development of critical target organ systems, particularly the renal system and RAS, explain the absence of definitive structural abnormalities in test animals.

International union of pharmacology. XLV. Classification of the kinin receptor family: from molecular mechanisms to pathophysiological consequences

Kinins are proinflammatory peptides that mediate numerous vascular and pain responses to tissue injury. Two pharmacologically distinct kinin receptor subtypes have been identified and characterized for these peptides, which are named B1 and B2 and belong to the rhodopsin family of G protein-coupled receptors. The B2 receptor mediates the action of bradykinin (BK) and lysyl-bradykinin (Lys-BK), the first set of bioactive kinins formed in response to injury from kininogen precursors through the actions of plasma and tissue kallikreins, whereas the B(1) receptor mediates the action of des-Arg9-BK and Lys-des-Arg9-BK, the second set of bioactive kinins formed through the actions of carboxypeptidases on BK and Lys-BK, respectively. The B2 receptor is ubiquitous and constitutively expressed, whereas the B1 receptor is expressed at a very low level in healthy tissues but induced following injury by various proinflammatory cytokines such as interleukin-1beta. Both receptors act through G alpha(q) to stimulate phospholipase C beta followed by phosphoinositide hydrolysis and intracellular free Ca2+ mobilization and through G alpha(i) to inhibit adenylate cyclase and stimulate the mitogen-activated protein kinase pathways. The use of mice lacking each receptor gene and various specific peptidic and nonpeptidic antagonists have implicated both B1 and B2 receptors as potential therapeutic targets in several pathophysiological events related to inflammation such as pain, sepsis, allergic asthma, rhinitis, and edema, as well as diabetes and cancer. This review is a comprehensive presentation of our current understanding of these receptors in terms of molecular and cell biology, physiology, pharmacology, and involvement in human disease and drug development.

Cardiovascular Pharmacotherapeutic Considerations During Pregnancy and Lactation

Table 2 summarizes the recommendations regarding the use of cardiovascular drugs during pregnancy and lactation.

Unexpected nephrotoxicity induced by tetrabromobisphenol A in newborn rats

The repeated dose toxicity of tetrabromobisphenol A (TBBPA), a flame retardant, was examined in male and female newborn rats given TBBPA orally at 0, 40, 200, or 600 mg/kg per day for 18 days from 4 days of age until weaning at 21 days of age. Half the rats in each dose group were sacrificed for a full gross necropsy and a histopathology on the organs and the tissues at 22 days of age and the remaining rats were reared without any treatment from post-weaning until 84 days of age to examine the recovery and the delayed occurrence of toxic effects. Treatment with 200 or 600 mg/kg TBBPA-induced nephrotoxicity characterized by the formation of polycystic lesions, and some deaths occurred in the 600 mg/kg group. There was no gender difference of nephrotoxicity and there were no other critical toxicities. At 85 days of age, nephrotoxic lesions were still present in the 200 and 600 mg/kg groups, but no abnormalities indicating delayed occurrence of toxic effects were found in the treated groups. In order to investigate the specificity of the nephrotoxicity induced by TBBPA in newborn rats, TBBPA was given to male and female young rats (5 weeks old) by oral administration at 0, 2000, or 6000 mg/kg per day for 18 days. The kidneys showed no histopathological changes even at the high dose. These results clearly indicate that the nephrotoxicity of TBBPA is specific for newborn rats although the toxic dose level was relatively high. To gain insight into the possible effects on human infants, the mechanism of this unexpected nephrotoxicity of TBBPA in newborn rats should be examined.

Enalapril: pharmacokinetic/dynamic inferences for comparative developmental toxicity. A review

Enalapril is an antihypertensive drug of the class of angiotensin-converting enzyme inhibitors (ACEI) used in pregnancy for treatment of pre-existing or pregnancy-induced hypertension. The use of ACE inhibitors (drugs that act directly on the renin-angiotensin system) during the second and third trimester of pregnancy in humans is associated with specific fetal and neonatal injury. The syndrome, termed "ACEI fetopathy" in humans, does not appear to have a similar counterpart in experimental animals. The present paper reviews pharmacokinetic and pharmacodynamic aspects of enalapril that are physiologically important during pregnancy and intrauterine development in humans and in experimental animal species with the aim of better understanding the comparability of the manifestations of enalapril developmental toxicity in animals and humans. The human fetus is at a disadvantage with regard to in utero enalapril exposure in comparison to some of the animal species for which gestational pharmacokinetic data are available. Important reasons for the higher vulnerability of the human fetus are its accessibility by enalapril and the earlier (relative to animal species) intrauterine development of organ systems that are specific targets of ACEI pharmacologic effect (the kidney and the renin-angiotensin system). In humans, these systems develop prior to calcarial ossification at the end of first trimester of pregnancy. The specific pharmacodynamic action of enalapril on these systems during fetal life is the chief determinant of the etiology and pathogenesis of ACEI fetopathy in humans. In contrast, in most of the studied animal species, these target systems are not developed until close to term when the fetus is relatively more mature (and therefore less vulnerable), so that the window of vulnerability is narrower in comparison to the human. Among animal species, the best concordance in fetal pharmacodynamics to the human is seen in the rhesus monkey, but further studies are necessary to determine if similar developmental pathology is induced in this animal model upon repeated administration of the drug during the relevant period of intrauterine development. Animal-human concordance of developmental toxicity is least likely in the rat because of greater disparities in enalapril availability to the fetus and the relative development of the kidney and skeletal ossification compared to that in humans.

Effects of fetal and neonatal renin-angiotensin system blockade in Lyon hypertensive rats

It has been shown that a brief period of angiotensin-converting enzyme (ACE) inhibition in growing spontaneously hypertensive rats (SHRs) induces long-term decrease of the blood pressure (BP) level. This study assessed whether persistent effects of ACE inhibition could be disclosed in Lyon genetically hypertensive (LH) rats treated from conception to age 3 weeks. ACE inhibition was obtained with captopril (100 mg/kg/24 h in the drinking water of the breeders) because this compound crosses the placental barrier. For each of the six treated pairs, the first litter was discarded, the second served as control, whereas the third and the fourth were obtained during captopril treatment. Six other pairs remained untreated. Aortic BP was beat-to-beat recorded in freely moving 14-week-old rats. It was observed that captopril reduced the number of newborns (42 in the second vs. 17 rats in the third litter of six LH pairs). BP and left ventricle weight did not differ between control and treated animals. It is concluded that, unlike SHRs, in LH rats, ACE inhibition is devoid of persistent effects on BP after cessation of the treatment.

Angiotensin II: a reproductive hormone too?

It has long been known that angiotensin II (Ang II) can affect reproductive tissues such as the uterus. However, the existence of a local renin-angiotensin system (RAS) in female as well as male reproductive tissues is a relatively recent observation. Of great interest is the discovery that all components of the RAS are present in the ovary, that the ovary secretes components of the RAS into the bloodstream, and that the ovary itself is responsive to Ang II. Recent studies suggest that the primary role of Ang II in the ovary is to cause atresia in non-ovulatory follicles; however, there is also compelling data to suggest that Ang II facilitates ovulation. Male reproductive structures also contain all of the components of the RAS, gonadotropins regulate the activity of these components, and these tissues have Ang II receptors. Of great interest is the expression of testis-specific angiotensin-converting enzyme (ACE), which is located on germ cells. Recent studies using gene knock-out techniques indicate that testis ACE plays an important role in male fertility. However, the overall significance of the RAS for normal reproductive function remains questionable. There is now a body of evidence implicating the RAS in pathophysiologies associated with reproductive function, which gives rise to the possibility that drugs acting on the RAS might ameliorate some of these disorders. Considerable work remains to determine the role of Ang II in reproductive functions.

The role of Angiotensin-converting enzyme in blood pressure control, renal function, and male fertility

Angiotensin-converting enzyme (ACE) is a zinc peptidase that plays a major role in the renin-angiotensin system. In mammals, the enzyme is present as two isozymes: a somatic form involved in blood-pressure regulation and a testis form of unknown function. Mice lacking ACE have been created and shown to have low systolic blood pressures and defects in renal development and function. These mice also have reduced male fertility, implicating the testis isozyme in reproductive function. (Trends Endocrinol Metab 1997;8:181-186). (c) 1997, Elsevier Science Inc.

Angiotensin II and its different receptor subtypes in placenta and fetal membranes

The recent discovery of a local renin-angiotensin system in trophoblastic tissues has raised many questions regarding its role in the physiology of normal gestation and its implications in the pathophysiology of hypertension during pregnancy. In this article, the authors first review the most interesting aspects of the chorioplacental renin-angiotensin system, dwelling on the tissue distribution of angiotensin II and its receptor subtypes in the placenta and fetal membranes of different species. The relationship between angiotensin II and other locally synthesized chorioplacental substances is also analysed and the therapeutic implications of phenomena observed in pregnancy-associated hypertension are discussed.

Excess extrafetal fluid without demonstrable changes in placental concentration gradients after week-long infusions of angiotensin into fetal lambs

It is known that a week-long infusion of angiotensin into fetal sheep produces polyhydramnios. The purpose of the present experiments was to determine whether an increased osmotic force across the placental barrier could account for the excess transfer of water. Six fetuses with indwelling catheters were infused with angiotensin-I and one with angiotensin-II; all, except one fetus in the first group, developed gross polyhydramnios. None of the transplacental concentration differences of the small plasma solutes Na+, Cl-, HCO3-, K+, urea, or glucose showed a demonstrable change and the same was true of the transplacental difference in freezing point osmolality and for the transplacental difference in plasma protein concentration. It is concluded that the infusion of angiotensin at a low dose rate is a reliable protocol for producing polyhydramnios. However, the present findings lend no support to the hypothesis that a primary change in transplacental osmotic force is the cause of the increased transplacental water transfer in this form of polyhydramnios. Alternative hypotheses are discussed in the light of recent discoveries.

Teratogen update: angiotensin-converting enzyme inhibitors

Occasionally there is a drug whose record in pregnancy is so frequently associated with adverse outcome of so specific a pattern that it becomes clear that its use must be restricted before scientific proof from epidemiological studies is obtained. I believe this to be the case with the drug class of ACEIs. There are mammalian models suggesting substantial fetotoxicity in a dose-related fashion. There is a strong and consistent pattern to the reported cases of ACEI-related adverse outcomes: the syndrome of oligohydramnios-anuria, neonatal hypotension, renal dysplasia, and hypocalvaria is too specific in association with the use of these drugs to be ignored. There is a very plausible biologic mechanism to explain the relationship. The features of ACEI fetopathy suggest that the underlying pathogenetic mechanism is fetal hypotension, which may also result from other exposures. Thus, while the fetopathy may not be truly specific to ACEIs, they are particularly liable to produce adverse fetal renal effects with their sequels (anuria-oligohydramnios, pulmonary hypoplasia, growth restriction) and hypocalvaria.

Risks of angiotensin-converting enzyme inhibition during pregnancy: experimental and clinical evidence, potential mechanisms, and recommendations for use

OBJECTIVE

To review reports on the use of angiotensin-converting enzyme inhibitors (ACE-I) during pregnancy in order to determine the incidence, nature, and potential mechanisms of fetal complications in an attempt to establish recommendations related to the use of these drugs during gestation.

DATA SOURCES

Relevant English-language articles identified through a Medline search and bibliographies found in recent articles.

STUDY SELECTION

Large number of reports both on animals and on humans have consistently shown a high degree of morbidity and even mortality in fetuses or newborns exposed to ACE-I during pregnancy. The reported complications include oligohydramnios, intrauterine growth retardation, premature labor, fetal and neonatal renal failure, bony malformations, limb contractures, persistent patent ductus arteriosus, pulmonary hypoplasia, respiratory distress syndrome, prolonged hypotension, and neonatal death. A high incidence of fetal complications was related to the use of ACE-I at all trimesters of pregnancy.

CONCLUSION

The gestational use of ACE-I may be associated with a high degree of fetal and newborn morbidity and even mortality. The use of these drugs should be avoided at all trimesters of pregnancy.

Renin-angiotensin system in neonatal rats: induction of a renal abnormality in response to ACE inhibition or angiotensin II antagonism

In experiments designed to analyze cardiovascular structure in response to antihypertensive therapy with an ACE inhibitor, we decided to start very early in life with the aim to prevent blood pressure increases and the development of vascular structural changes. In these treated groups of rats we unexpectedly observed that after they were weaned, their water consumption and urine volume, respectively, increased substantially. The present study was designed to determine if inhibition of the renin-angiotensin system produced similar effects in different strains of rats, and focused on characterizing the abnormal fluid balance occurring as a consequence to neonatal treatment with ACE inhibitors or angiotensin II blockers. Three-day-old Wistar Kyoto (WKY), Wistar (WR) and spontaneously hypertensive rats (SHR) were given either saline, enalapril, captopril, losartan and the AT2 blocker, PD123319, in the same amount of volume for 20 days. Treatment was stopped and rats were examined with regard to renal morphology at 4, 14 and 30 weeks of age. In addition, water consumption, urine volume, urine electrolytes and osmolality were analyzed at 14 weeks of age, that is, 10 weeks off treatment. Early treatment with the ACE inhibitors, enalapril and captopril, and the AT1 blocker, losartan, but not the AT2 blocker, PD 123319, in the SHR and in the normotensive strains WKY and WR produced persistent, irreversible histopathological renal abnormalities in adult life, long after the rats had been taken off treatment. These abnormalities consisted of mainly cortical tubulointerstitial inflammation, various degrees of papillary atrophy and pelvic dilation.(ABSTRACT TRUNCATED AT 250 WORDS)