Role of primary and secondary maternal viremia in transplacental guinea pig cytomegalovirus transfer.

The modulation of the outcome of intrauterine guinea pig cytomegalovirus (GPCMV) infection by maternal viremia was investigated in the guinea pig model. Virus assay and in situ hybridization were used to study GPCMV infection of maternal blood, placentas, and fetuses following inoculation of pregnant guinea pigs by the subcutaneous, intracardiac, or intranasal route. Animals were inoculated in early gestation and were evaluated every 7 to 10 days throughout pregnancy. Although placental and fetal infections occurred in all groups examined, transfer of GPCMV to placentas and fetuses was most efficient in mothers inoculated subcutaneously. Primary viremia was followed by virus clearance from blood and by an episode of secondary viremia in the three groups of mothers examined. Placental and fetal infections in animals infected subcutaneously or intracardially were first detected at the time of primary viremia, persisted throughout gestation, and increased during secondary viremia. In contrast, placental and fetal infections in animals inoculated intranasally were demonstrated primarily during secondary viremia. Fetal infection was detected in all mothers with detectable primary and secondary viremia but in only 33% of mothers that experienced only primary viremia. These results suggest that secondary maternal viremia is associated with increased placental and fetal GPCMV infections.     

Characterization of guinea pig cytomegalovirus DNA.

The genome of guinea pig cytomegalovirus (GPCMV) was analyzed and compared with that of human cytomegalovirus (HCMV). GPCMV and HCMV DNAs were isolated from virions and further purified by CsCl centrifugation. Purified GPCMV DNA sedimented as a single peak in a neutral sucrose gradient and was infectious when transfected into guinea pig embryo fibroblast cells. The cytopathology was characteristic of that seen after infection with GPCMV. Virus DNA purified from virions isolated from infected GPEF or 104C1 cells had a CsCl buoyant density of 1.713 g/cm3, which corresponds to a guanine plus cytosine content of 54.1%. The CsCl buoyant density of GPCMV DNA was slightly less than that of HCMV DNA (1.716 g/cm3), but sufficiently different so that the two virus DNA peaks did not coincide. GPCMV DNA cosedimented with T4 DNA in a neutral sucrose gradient. Restriction endonuclease cleavage of GPCMV or HCMV DNAs with HindIII, XbaI, or EcoRI yielded fragments easily separable by agarose gel electrophoresis and ranging from 1.0 X 10(6) to 25.8 X 10(6) daltons. The number, size, and molarity of GPCMV DNA fragments generated by restriction enzymes were determined. Hybridization of restriction endonuclease-cleaved GPCMV DNA with radioactively labeled HCMV DNA and, conversely, hybridization of restriction endonuclease-cleaved HCMV DNA with radioactively labeled GPCMV DNA indicated sequence homology between the two virus DNAs.     

Pathogenesis of cytomegalovirus-associated labyrinthitis in a guinea pig model

Cytomegalovirus infects fetuses through the placenta, resulting in various congenital disorders in newborns, including hearing loss. We developed a monoclonal antibody to guinea pig cytomegalovirus (GPCMV) that was available for immunohistochemistry, and investigated the expression of the GPCMV antigen in animal models of direct and congenital infections. Injection of GPCMV, directly to the inner ear, increased the sound pressure level and resulted in labyrinthitis with severe inflammation. Immunohistochemistry detected GPCMV-infected cells mainly in the scala tympani, scala vestibule and spinal ganglion, but rarely in the cochlear duct. Injection of GPCMV to 5-week pregnant guinea pigs resulted in severe labyrinthitis in fetuses. Immunohistochemistry detected GPCMV-infected cells in the perilymph area and spinal ganglion, but not in the endolymph area, including hair cells. These data suggest that the virus spreads via the perilymph and neural routes in the inner ear of both models of direct and congenital infections.     

Testosterone synthesis in vitro by the fetal testis of the guinea pig

Synthesis and secretion of testosterone by testes of guinea pig fetuses were studied in organ culture. The amount of testosterone secreted into the culture medium was estimated by radio-immunoassay. It was demonstrated that testosterone was already secreted by testes explanted at 25 days. The amount of testosterone secreted during the first day in culture by testes from fetuses of different ages (25–30 days) increased with fetal age. The amount of testosterone extracted from fetal guinea pig testes at ages used for explantation (25–30 days) were much lower than the amount secreted during the first 24 hours in culture. During subsequent days in culture, an increase in the amount of testosterone secreted was observed only for testes explanted at 25 days. The amount secreted by testes from older fetuses (26–30 days) stayed constant or decreased. Aminogluthetimide phosphate (100 μM) decreased significantly testosterone secretion by testes explanted at 25 days.These findings indicate that the capacity for biosynthesis of testosterone is present in fetal guinea pig testes at 25 days and increases during the subsequent days.     

Pathogenesis of guinea pig adenovirus infection

BACKGROUND AND PURPOSE: The existence of guinea pig adenovirus (GPAdV) has been suspected on the basis of histopathologic findings, but the virus has not yet been isolated. In susceptible animals, it may cause severe bronchopneumonia and death. Adenovirus-like inclusion bodies have been observed in the lungs of animals with clinical disease. Prevalence of the infection is unknown. Recently, a polymerase chain reaction (PCR) assay was described that was able to selectively detect GPAdV. METHODS: To investigate the pathogenesis of GPAdV, we inoculated eight guinea pigs with GPAdV; eight control animals were sham inoculated. The PCR assay was used to trace the infection. In a second experiment, transmission of GPAdV from an experimentally infected animal to five immune-naive cohorts was examined. RESULTS: None of the infected animals developed clinical disease. The GPAdV could be detected by PCR analysis of nasal-swab specimens on days 6 through 15 after infection. Infective virus could be recovered from the nasal mucosa during this period (as determined by inoculation of immune-naive animals). The virus was transmitted from an experimentally infected animal to two of five immune-naive cage mates. CONCLUSION: The GPAdV may cause transient subclinical upper respiratory tract infection that may descend to the lungs.     

Ontogeny of pituitary gonadotrophin secretion in the fetal and post-natal pig in response to LHRH in vitro

Monolayer cultures of anterior pituitary cells from male or female pigs of 60, 80, 105 days of fetal life or of 60, 160 and 250 days of post-natal life were prepared and treated with LHRH (1 pM to 10 nM). Dose-related increases of LH were first seen at 80 days of gestation in both sexes, while only female fetuses responded to maximal LHRH at 60 days. Basal and stimulated LH release doubled in cultures from 105-day-old fetuses when compared with those at 80 days. Compared to late fetal stages LH release was 20- to 30-fold higher in cell cultures from 60-day-old (post-natal) donors without further change during the post-natal period. In all pre- and post-natal age groups basal and maximal LH release of pituitary cells from males was lower than that of females. FSH stimulation started in male and female cells at 80 days of gestation only at LHRH concentrations exceeding or equal to 0.1 nM. By 105 days FSH secretion was dose-related and pituitary cells of females responded with higher FSH values than did those of males. In general, post-natal cells released much higher amounts of FSH than did prenatal cells. Basal and maximal release of FSH decreased during post-natal development in both sexes. Basal as well as maximal FSH release of cultures from female donors was higher than that found in cultures from male donors. Determination of total LH and FSH content in fetal pituitary cell cultures indicated that the developmental increase in gonadotrophin release potential is a function of the total gonadotrophin content in vitro. We conclude that (1) the in-vitro release of gonadotrophins to LHRH is dose-, age- and sex-dependent; (2) in the female fetal pig LH responsiveness develops earlier than FSH responsiveness; (3) apparently, these maturational changes mainly reflect alterations in pituitary gonadotrophin content; and (4) there is no simple relationship between in-vitro release and circulating gonadotrophins.     

The development of adipocytes in primary stromal-vascular culture of fetal pig adipose tissue

Primary cultures of stromal-vascular cells of adipose tissue from fetuses at 70 and 110 days of gestation were evaluated as potential model systems for studies of fetal adipocyte differentiation and proliferation. In the cultures, fat cells developed as very discrete clusters. Fat cell cluster development was dependent on initial cell density and time. Histochemical analysis for NADP-dependent dehydrogenases revealed an age of donor effect. Similar levels of enzymes (malate and glucose-6-phosphate dehydrogenase) were apparent in fat cell clusters and stromal cells in cultures of cells from fetuses at 70 days of gestation. These enzymes were only present in fat cell clusters in cultures of cells from fetuses at 110 days of gestation. The distribution of histochemically detectable esterase activity was dependent on the cell density at time of analysis. In areas of high cell density, esterase was restricted to fat cell clusters whereas, both stromal cells and fat cells were esterase reactive in areas of low cell density. Omitting PMS from the dehydrogenase media revealed differences in enzyme reactions of cells grown on collagen-coated and uncoated glass surfaces. These studies demonstrate that primary cultures of stromal-vascular cells from 110-day-old fetuses would be a useful system to identify factors involved in adipocyte proliferation and differentiation.     

Changes in permeability of fetal guinea pig skin during gestation

Permeability of fetal skin to tritiated water was measured in vitro using samples taken from the back and flanks of 21 guinea pig fetuses whose gestational age ranged from 30 to 67 days (term = 68 days). From 30 to 45 days, fetal skin was relatively permeable to water, with a permeability coefficient for unidirectional, diffusional transfer of labelled water that averaged 0.372 +/- 0.041 (SEM) X 10(-4) cm/s. Then during a 5-10 day interval, the measured permeability coefficient decreased abruptly to very low and barely detectable levels. These changes took place at the time during gestation when others have shown the skin becomes keratinized and growth of new hair follicles is completed. Thus these findings are consistent with a relatively free exchange of water between amniotic fluid and fetal interstitium across the skin during the first two-thirds of gestation and then with further maturation an abrupt functional separation between these fluid compartments during the last third of gestation.     

Ovarian development in control and decapitated pig fetuses

Ovarian development was studied in control and decapitated pig fetuses. Fetuses were decapitated at 42 days postcoitum. At 51, 61, 74, 90 and 112 days postcoitum decapitated and control females were collected. Ovarian weight gradually increased during development in control animals. Deprivation of pituitary hormones as a result of fetal decapitation did not cause a decline in ovarian weight increase. Germ cell maturation in control and decapitated fetuses proceeded in a similar fashion, with secondary follicles being the most advanced stage. Enzyme histochemical activity was present in the primary interstitial gland cells and in granulosa cells and was similar in normal and decapitated fetuses. Both NADH diaphorase activity and 3 beta-hydroxysteroid dehydrogenase activity increased from 51 to 74 days and remained relatively constant thereafter. Since fetal decapitation in the pig hardly influences ovarian development, pituitary dependency of the fetal ovary in the pig is unlikely.     

Characterization of the guinea pig cytomegalovirus genome by molecular cloning and physical mapping.

Fragments of guinea pig cytomegalovirus (GPCMV) DNA produced by HindIII or EcoRI restriction endonuclease digestion were cloned into vectors pBR322 and pACYC184, and recombinant fragments representing ca. 97% of the genome were constructed. Hybridization of 32P-labeled cloned and gel-purified HindIII, EcoRI, and XbaI fragments to Southern blots of HindIII-, EcoRI-, and XbaI-cleaved GPCMV DNA verified the viral origin of cloned fragments and allowed construction of HindIII, EcoRI, and XbaI restriction maps. On the basis of the cloning and mapping experiments, the size of GPCMV DNA was calculated to include 239 kilobase pairs, corresponding to a molecular weight of 158 X 10(6). No cross-hybridization between any internal fragments was seen. We conclude that the GPCMV genome consists of a long unique sequence with terminal repeat sequences but without internal repeat regions. In addition, GPCMV DNA molecules exist in two forms. In the predominant form, the molecules demonstrate sequence homology between the terminal fragments; in the minor population, one terminal fragment is smaller by 0.7 X 10(6) daltons and is not homologous with the fragment at the other end of the physical map. The structural organization of GPCMV DNA is unique for a herpesvirus DNA, similar in its simplicity to the structure reported for murine cytomegalovirus DNA and quite dissimilar from that of human cytomegalovirus DNA.     

Ontogeny of androgen receptors in fetal guinea pig brain

Sexual differentiation of the guinea pig brain is androgen dependent. To understand the cellular mechanisms of androgen action, we studied the ontogeny of cytosolic (ARc) and nuclear (ARn) androgen receptors in the brains and anterior pituitaries of fetal, neonatal, and adult guinea pigs. Using cytosol from the hypothalamus-preoptic area-amygdala-septum of 60- to 65-day fetuses and nuclear preparations from 6-day-old neonates treated with testosterone propionate, validation studies revealed an AR with an apparent Kd of 1.9 +/- 1.1 (mean +/- SEM, n = 3) x 10(-10) M (ARc) and 3.4 +/- 3.2 (n = 3) x 10(-10) M (ARn). The cytosolic receptors were highly specific for androgens. After assay validation, AR content was determined from specific brain regions of fetuses obtained on Days 30, 40, 50, and 59 of gestation and on Days 6 and 120 postpartum. ARc differed significantly (p less than 0.05) between brain regions and times of gestation, but no sex differences were apparent. In contrast, ARn showed little difference between tissues or with gestational age, but there were significant differences between males and females, especially in late gestation and early postnatal life, with males having greater ARn binding (p less than 0.05). These data demonstrate the presence of ARc and ARn in the fetal brain and pituitary gland during the critical period of sexual differentiation (Days 30-37 of gestation), thus establishing the identity of cellular structures involved in androgen action.     

Effects of exogenous steroids on androgen receptors in fetal guinea pig brain

We treated pregnant guinea pigs on Day 50 of gestation with 10 mg testosterone propionate (TP), obtaining fetuses 2, 4, 8, or 18 h later as well as after 5 days of treatment. In a second group of pregnant guinea pigs, dihydrotestosterone propionate (DHTP), estradiol benzoate (E2B), progesterone (P), or cortisol was given 2 h before obtaining fetuses. Although TP treatment elevated fetal serum T (p less than 0.05), brain cytosolic androgen receptor (ARc) content was unchanged in fetuses of either sex. In female fetuses, nuclear androgen receptors (ARn) increased 10-fold in medial-basal hypothalamus (MBH) and preoptic area (POA) at 2 and 4 h (respectively) after treatment, while fetal male ARn content was unchanged. Maternal injection of other steroids (E2B, P, or cortisol, but not DHTP) significantly increased these hormones in the fetus 2 h later (p less than 0.05). Only androgens affected fetal androgen receptor (AR) content. While TP increased ARn in female MBH, DHTP decreased ARc in fetal anterior pituitary of both sexes. In this latter case, a metabolite of DHT may mediate the effects. We conclude that T crosses the guinea pig placenta and activates ARn in POA and MBH of female fetuses; male ARn appear to be maximally occupied by endogenous T. Steroids of other classes do not induce AR responses in fetal guinea pig brain. These AR changes may represent an initial cellular mechanism in brain sexual differentiation.     

The ultrastructure of normal fetal and neonatal pig testis germ cells and the influence of fetal decapitation on the germ cell development

The development of germ cells in the male pig was investigated ultrastructurally in normal and decapitated fetuses. The age ranged respectively from 30 days p.c. till one month after birth and from 52 days p.c. until birth. The ultrastructural organization of the germ cells changes dramatically between 30 days p.c. and 52 days p.c. which coincides with the formation of 'true' sex cords. From 52 days p.c. onwards the morphology is rather stable: cells show a 'hydrated' appearance and typical cell bridges. There is no obvious difference in the ultrastructure of germ cells in decapitated animals, their normal littermates and control animals. Therefore germ cell development in the pig is likely to be insensitive to gonadotropins during the fetal period. The development of pig germ cells follows closely the pattern described for several species. Quantitatively there is an increase in the ratio of germ cell/Sertoli cell per cross sectional diameter in the decapitated animals.     

Estrogen responsiveness of fetal guinea pig uterine cells in culture

Cells from the uterus of the guinea pig fetus have been grown as a monolayer culture in serum-containing medium. Cells from the first subculture showed high concentrations of progesterone receptor (PR; 9.3-13.8 pmol/mg DNA) even after 9 days in medium containing charcoal-treated serum and estradiol did not induce any further increase. The antiestrogens, tamoxifen and monohydroxytamoxifen, both had an inhibitory effect which could be overcome by estradiol. The progestins, progesterone and R5020, as well as the antiprogestin, RU38486, also decreased the PR concentration. Estrogen receptor (ER) levels did not vary with the compounds tested but were found to be low compared to concentrations found in the fetal guinea pig uterus at 55-65 days of gestation. None of the compounds tested had any effect on the growth of the fetal uterine cells so that the modulation of PR concentrations was dissociated from the regulation of cell growth. It is concluded that estrogens are necessary but not sufficient factors in the control of PR levels in fetal uterine cells. The establishment of a culture system for separate types of fetal uterine cells will permit us to study in vitro the factors involved in the growth effects of estrogens and the control of PR synthesis.     

Modulation of the progesterone receptor in the fetal uterus of the progesterone-primed guinea pig in vivo and in organ culture

Guinea pig fetuses were treated with progesterone for 7 days before placing fetal uteri in organ culture to see if progesterone pre-treatment of fetuses in utero would permanently inhibit the spontaneous rise in progesterone receptor which occurs in organ culture. The data show that: the basal level of progesterone receptor in fetal uteri was not affected by the progesterone treatment and progesterone receptor concentrations in vitro were also not inhibited. When guinea pig fetuses were treated sequentially with progesterone and estradiol, estradiol failed to provoke an uterotrophic effect but it retained its ability to stimulate progesterone receptor concentrations.     

Kainate receptor modification in the fetal guinea pig brain during hypoxia

The present study tests the hypothesis that hypoxia alters the high-affinity kainate receptors in fetal guinea pig brain. Experiments were conducted in normoxic and hypoxic guinea pig fetus at preterm (45 days of gestation) and term (60 days of gestation). Hypoxia in the guinea pig fetus was induced by exposure to maternal hypoxia (FiO₂=7%) for 60 min. Brain tissue hypoxia in the fetus was documented biochemically by decreased levels of ATP and phosphorreatine. [³H]-Kainate binding characteristics (Bmax=number of receptors, Kd=dissociation constant) were used as indices of kainate receptor modification. P₂ membrane fractions were prepared from the cortex of normoxic and hypoxic fetuses and were washed six times prior to performing the binding assays. [³H]kainate binding was performed at 0°C for 30 min in a 500 l medium containing 50 mM Tris-HCl buffer, 0.1 mM EDTA (pH 7.4), 300 g protein and varying concentrations of radiolabelled kainate ranging from 1 to 200 nM. Non-specific binding was determined in the presence of 1.0 mM glutamate. During brain development from 45 to 60 days gestation, Bmax value increased from 330±16 to 417±10 fmoles/mg protein; however, the Kd was unchanged (8.2±0.4 vs 8.8±0.5 nM, respectively). During hypoxia at 60 days, the Kd value significantly increased as compared to normoxic control (15.5±0.7 vs 8.8±0.5 nM, respectively), whereas the Bmax was not affected (435±12 vs 417±10 fmol/mg protein, respectively). At 45 days, hypoxia also increased the Kd (11.9±0.6 vs 8.2±0.4 nM) without affecting the Bmax (290±15 vs 330±16 fmol/mg protein, respectively). The results show that the number of kainate receptors increase during gestation without change in affinity and demonstrate that hypoxia modifies the high-affinity kainate receptor sites at both ages; however the effect is much stronger at 60 days (term). The decreased affinity of the site could decrease the kainate receptor-mediated fast kinetics of desensitization and provide a longer period for increased Na⁺-influx, leading to increased accumulation of intracellular Ca²⁺ by reversal of the Na⁺–Ca²⁺ exchange mechanism. In addition, Kd values for kainate-type glutamate receptor sites are 30–40 fold lower (i.e. higher affinity) than those for NMDA-displaceable glutamate sites. The higher affinity suggests that the activation of the kainate-type glutamate receptor during hypoxia could precede initiation of NMDA receptormediated excitotoxic mechanisms. We propose that hypoxia-induced modification of the high affinity kainate receptor in the fetus is a potential mechanism of neuroexcitotoxicity.     

NMDA receptor modification in the fetal guinea pig brain during hypoxia

The effect of maternal hypoxia on the modification of the fetal brain cell membrane N-methyl-d-aspartate (NMDA) receptor and its modulatory sites was investigated. Experiments were conducted in pregnant guinea pigs of 60 days of gestation. Guinea pig fetuses were exposed to maternai hypoxia (FiO₂=7%) for 60 minutes. Tissue hypoxia in the fetal brain was documented biochemically by decreased levels of ATP and phosphocreatine (91.3% and 88.6% lower than normoxia, respectively). MK-801 binding characteristics (Bmax = number of receptors, Kd = affinity of receptor) were used as an index of NMDA receptor modification. P2 membrane fraction was prepared from the cortex of normoxic and hypoxic fetal brain and washed thoroughly before carrying out the binding assay. In hypoxic brains, Bmax decreased from the normoxic control level 0.79±0.03 pmol/mg protein to 0.58±0.03 pmol/mg protein (P<0.005) and Kd value decreased (increased affinity) from 8.54±0.27 nM to 4.01±0.23 nM (P<0.005) respectively. The MK-801 binding in the absence of added glutamate and glycine in hypoxic brain was 100% higher as compared to controls, indicating an increased sensitivity of the NMDA receptor to activation. The spermine dependent maximum activation of the NMDA receptor increased to 44% in the hypoxic animals as compared to 25% in controls. The Mg²⁺ response of the NMDA receptor was not affected by hypoxia. The increased affinity and increased basal activation (tone) of the NMDA receptor during hypoxia, as well as its increased activation by spermine, would hyperstimulate the NMDA receptor-ion channel complex function which could increase the susceptibility of the fetal brain to hypoxia. The results of this study indicate that hypoxia causes differential and selective modification of specific sites (recognition, co-activator, and modulatory) of the NMDA receptor ion channel complex. The hypoxia-induced modification of the NMDA receptor modulatory sites appears to be the potential mechanism of neuroexcitotoxicity.     

Oxytocin-induced labor augments IL-1beta-stimulated lung fluid absorption in fetal guinea pig lungs

We tested the hypothesis that oxytocin-induced labor augmented IL-1beta-induced/-stimulated lung fluid absorption in preterm guinea pig fetuses. IL-1beta was administered subcutaneously daily to timed-pregnant guinea pigs for 3 days with and without simultaneous cortisol synthesis inhibition by metyrapone. At day 3, oxytocin was administered, and fetuses were delivered by abdominal hysterotomy at 61 and by oxytocin-induced birth at 68 days gestation. Delivered fetuses were instilled with isosmolar 5% albumin into the lungs, and lung fluid movement was measured over 1 h by mass balance. Lung fluid absorption was induced in 61-day and stimulated in 68-day gestation lungs by IL-1beta. Labor induction by oxytocin augmented IL-1beta-induced/-stimulated lung fluid absorption. Metyrapone pretreatment did not affect oxytocin-induced/-stimulated lung fluid absorption, while completely blocking IL-1beta-induced/-stimulated fluid absorption. Fetal lung fluid absorption, when present, was always propranolol and amiloride sensitive, suggesting that beta-adrenoceptor stimulation and amiloride-sensitive sodium channels were critical for fluid absorption. Epithelial sodium channel and Na-K-ATPase subunit expressions were both increased by IL-1beta, but not further by oxytocin. Our results indicate that IL-1beta release into the maternal blood circulation positively affects lung maturation due to the IL-1beta-induced release of cortisol and thus prepares the lungs for the epinephrine surge associated with labor.     

Selective changes to phosphatidylcholine and phosphatidylethanolamine molecular species in the developing fetal guinea pig liver and plasma

The molecular species composition of membrane phospholipids influences the activities of integral proteins and cell signalling pathways. We determined the effect of increasing gestational age on fetal guinea pig liver phosphatidylcholine (PC) and phosphatidylethanolamine (PE), and plasma PC molecular species composition. The livers were collected from fetuses (n = 5/time point) at 5 day intervals between 40 and 65 days of gestation, and at term (68 days). Hepatic PC and PE molecular species composition was determined by electrospray ionisation mass spectrometry. An increasing gestational age was accompanied by selective changes in individual molecular species. The proportion of the sn-1 18:0 species increased relative to the sn-1 16:0 species in liver PC, but not PE, with an increasing gestational age. 1-O-alkyl-2-acyl PC species concentrations decreased significantly between 40 and 45 days of gestation (40%), and 65 and 68 days (54%). Total 1-O-alkenyl-2-acyl PE species concentration increased between days 60 and 65, due to a rise in 1-O-16:0 alkyl/20:4 content, and then decreased until term. Between day 40 and term, PC and PE sn-2 18:2n-6 species concentrations increased 3-fold. PC16:0/18:2 increased gradually throughout gestation, while PC18:0/18:2 content only increased after day 65. The overall increase in PE18:2n-6 content was due to PE18:0/18:2 alone. The composition of plasma PC essentially reflected hepatic PC. Overall, these data suggest differential regulation of hepatic PC and PE molecular species composition during development which is essentially independent of the maternal fatty acid supply.