Betty Bernard

Biochemical properties of arginase in human adult and fetal tissues.

Abstract Data comparing the kinetic, physical, and chemical properties of arginase, ( l -arginine ureahydrolase; EC 3.5.3.1) the last enzyme of the urea cycle, in human adult and fetal liver, kidney, brain, and gastrointestinal tract are reported. The arginases demonstrated similar pH optima in vitro , greater than 9.5; requirement for a metal cofactor, Mn 2+ ; biphasic denaturation curves at 68°C in the absence of MnCl 2 ; exponential denaturation curves at 81°C in the presence of 20 m m MnCl 2 ; and similar K m for arginine, 8–18 m m , and K i s for lysine and ornithine, 1–20 m m . The arginases differed in their electrophoretic mobility in polyacrylamide gels at basic pH (8.6) and acid pH (5.6).

MATERNAL-FETAL HEMORRHAGE: INCIDENCE AND SENSITIZATION

Observations indicate that the first born RhO (D)-positive (Rh+) infant of an RhO. (D)-negative (Rh-) mother may have a higher risk of hemolytic disease if the grandmother is Rh+ rather than Rh-. This “grandmother theory” gives rise to the speculation that the primary sensitizing dose of Rh+ blood was received in-utero by the Rh- baby from the Rh+ mother. To investigate the incidence and the timing of a possible maternal-fetal transfusion and its resultant antibody stimulation in the Rh- infant born of an Rh+ mother, 402 infant serums (292 at birth and 110 at 2 days) were studied for presence of anti-D antibody (modified Lalezari method) and retested in 237 patients at 1-6 months of age. In addition, 275 blood samples from 2 day old infants were tested for presence of maternal Rh+ red cells (fluorescein labeled anti-globulin technic). Although several reactions initially appeared to identify antibody, none of these proved to be anti-D when these serums were tested with a 10 red-cell panel. Maternal Rh+ red cells were detected in 3 neonatal blood samples (1.1%), but no anti-D antibody was found in these 3 babies on follow-up-at 1, 3 and 6 months in 2 babies or at birth and 4 months in the other. Published reports indicating a significant risk for parturition sensitization of the Rh- neonate of the Rh+ mother cannot be corroborated by our studies.(Support:Ortho Diagnostics)

231 PHARMACOKINETICS OF AQUEOUS PENICILLINS IN CEREBROSPINAL FLUID OF NEONATES

If central nervous system (CNS) involvement is suspected in congenital syphilis, both aqueous penicillin G (APG) and aqueous procaine penicillin G (APP) are recommended for treatment. To study pharmacokinetics after administration of APG and APP, single samples of cerebrospinal fluid (CSF) and serum of 21 infants treated for congenital syphilis were obtained 1½ to 6 hrs. following a single IM dose of 50,000 units/kg body weight. Only one baby was symptomatic. Serum levels and half-lives of APG and APP were within the ranges reported for term infants. Treponemacidal levels after APG (≥.03 ug/ml) were detected in 11 CSF specimens in the first sample at ½ hr. and persisted through the 6 hr. study. A peak CSF level of 0.17 ug/ml was found at 2½ to 3 hrs. with an estimated half-life of 1½ hrs. After APP, penicillin activity was not detected in 5 CSF samples between ½ to 1 hr., but was present by 1½ hrs. Only 2 of 9 samples reached APP levels of ≥.03 ug/ml; in these two, a peak of 0.08 ug/ml was reached at 2½ hrs. These preliminary data show that both penicillins will provide treponemacidal levels in the serum, but APG reaches a higher CSF level and persists for a longer time. APG appears to be a more appropriate drug for treatment of congenital syphilis with suspect or proven CNS involvement.(*Current address: UCLA Sch. of Med., Dept. of Pediatrics)

579 INTRAUTERINE OR INTRAPARTUM Rh ISO-SENSITIZATION AND USE OF MICRhoGAM IN THE NEONATE

To investigate incidence and timing of a possible transfusion of Rho (D)-positive (Rh+) maternal cells to a fetus with Rho (D)-negative (Rh-) cells and the role of Rho (D) immune globulin in prevention of potential primary sensitization, 354 Rh-infants born to Rh+ mothers were studied. MICRhoGAM (MRG) (50ug) was administered to 114 female infants in the first 72h. of life and 240 infants were controls (52 females, 188 males). Of 263 cord serums screened, antibody was found in 6, none of which were anti-D on retesting against a 10 red-cell panel. Two of 167 heel stick samples obtained from infants at 2 days of age revealed maternal Rh+ cells (courtesy B.Clauss & E.R. Jennings). No anti-D antibody was found in either infant at 3 and 6 mo. of age. No anti-D was found in 207 serum samples from control infants (158 males, 49 females) who were ½ to 17 mo. of age; however, 26 of 94 MRG recipients had anti-D between 2½ and 5 mo. of age. (RhoGam may be detected up to 6 mo.) Reports indicating significant risk for either intrauterine or parturition primary anti-D sensitization cannot be corroborated by our studies. Primary sensitization not presently detectable may be confirmed later by an amnestic anti-D response on a second exposure to Rh+ cells, perhaps during pregnancy with a Rh+ fetus. Long term follow-up will ultimately decide the immunoprophylactic role of MRG in prevention of Rho (D) iso-sensitization.

Metabolic Crises in the Neonate: Thermoregulation and Hypoglycemia

Next to successful neonatal resuscitation, the two most critical life-support systems essential for the neonate’s ultimate survival and potential are those concerned with thermoregulation and glucose homeostasis. To minimize the stresses of adaptation to an extrauterine life from the maternal source of heat and energy, a well-organized program of management must be instituted in the delivery room and continued in the nursery. The smaller or the more compromised the neonate, the more critical is the need for protocol, personnel, and equipment to provide a minimum of cold stress from the moment of birth and to begin to monitor blood glucose by the first 30–60 min of life. The healthy term infant can and does benefit from such a program, with broader parameters.

PREDICTORS OF GENTAMICIN EXCRETION IN SICK NEWBORNS

To improve gentamicin (GMS) dosage regimens in neonates, data from 46 infants requiring GMS therapy were analyzed for K2 (.693/half-time) using the model:Dose K1 Body Volume of Distribution (Vd) K2 Excretion.K1=1.8 hours−1 and Vd=14.7% of body weight.K2 (hrs.−1) was calculated to fit the serum level found. The patients were 1-14 days old (mean 5.5), with a gestational age (GA) of 29-42 weeks (mean 37.9) and a serum creatinine of ≥0.5 mg/dl. A serum GMS level was drawn 3-12 hours into the dose interval.Fourteen clinical parameters were examined by stepwise multiple regression (SBC Call-370 Statpack). Estimated creatinine clearance (CCr), computed as described earlier by this laboratory, was 6-34 ml/min./1.73 M2 (mean 17) and correlated best with K2. Other predictors, in order, were weight/length percentile (WL), GA, age (A) and sex (S, female=0. male=1). K2=.32838 + .00276CCr -.00167WL + .01792GA + .01893A -.07038S (r=.553, S.E.E.=137, P<.001). Based on this data, GMS half-time ranged from 0.81 to 5.13 hours with a mean of 1.82 hours. These findings have been incorporated into a computer program to permit computation of K2 for GMS with reasonable accuracy to allow initial or subsequent planning of GMS dosage regimens for sick newborn infants. (Research Support: USPHS #MB00146)

PROPERTIES OF HUMAN ADULT AND FETAL RED BLOOD CELL ARGINASE: A POSSIBLE DIAGNOSTIC TEST FOR ARGINASE DEFICIENCY

Hyperargininemia due to arginase deficiency results in a syndrome of progressive neurological and intellectual deterioration and is inherited in an autosomal recessive manner. Arginase activity is deficient in liver and red and white blood cells. Its activity in normal skin fibroblasts is barely detectable and is undetectable in amniotic fluid cells.Heparinized blood was obtained from five healthy fetuses between 14 and 20 weeks gestation at the time of therapeutic abortion by hysterotomy. Normal adult blood specimens were used as controls.The specific activity for the fetal specimens was 0.35-5.20 mmoles urea/gm Hb/hr compared to 3.00 in adult samples. The pH maximum of one fetal and one adult blood with Mn++ activation was 9.5-10.0. In the fetal samples, the activity with Co++ as the divalent cation was 83% that of Mn++ at pH 7.5 and 44% at pH 9.5. The comparable figures for adult blood were 96% and 63%. Activity with Ca++ and Mg++ was minimal for all specimens at pH 9.5. The apparent Km for arginine at pH 9.5 with Mn++ was 14×10−3M for two adult samples and ranged from 10-19×10−3M for four fetal specimens.Arginase in adult and fetal red cells may be specified by a single genetic locus. Therefore, fetal blood may be a suitable tissue for prenatal diagnosis of this disease.