Activation of the 5-HT1C receptor expressed in Xenopus oocytes by the benzazepines SCH 23390 and SKF 38393.

1. A cloned 5-HT1C receptor expressed in Xenopus laevis oocytes was used to characterize the action of four dopamine D1-selective benzazepines at the 5-HT1C receptor. Additionally, the apparent binding of the D1-selective benzazepines to 5-HT1C receptors was measured in the choroid plexus of the pig. 2. In voltage-clamped oocytes expressing the cloned 5-HT1C receptor, 5-hydroxytryptamine (5-HT) elicited a characteristic inward current response with an EC50 of 13 nM. SCH 23390 acted as a stereoselective agonist (or partial agonist) with an EC50 of about 550 nM. SKF 38393 (1 microM-1 mM), SKF 77434 (100 microM), and SKF 82958 (100 microM) also acted as agonists (or partial agonists) at the cloned 5-HT1C receptor. SKF 38393 was not stereoselective at the 5-HT1C receptor. 3. The response to SCH 23390 activated slowly and, although the response contained many oscillations characteristic of the activation of the phosphatidylinositol signal transduction system, SCH 23390 rarely elicited the rapid spike-like response seen routinely in response to 5-HT. However, the responses to SKF 38393, SKF 77434, and SKF 82958 were identical in appearance to the response to 5-HT, except that the responses to the benzazepines were smaller. These comparisons were made by applying both a benzazepine and 5-HT to each individual oocyte expressing the cloned 5-HT1C receptor. 4. Consistent with the responses measured in oocytes, SCH 23390 bound stereoselectively to 5-HT1C receptors in the choroid plexus of the pig (Ki = 6.3 nM), and SKF 38393 bound non-stereoselectively with lower affinity (Ki = 2.0-2.2 microM).5. It is concluded that while these benzazepines demonstrate selectivity for the dopamine D1 receptor, they also can act as agonists or partial agonists at the 5-HT1c receptor in situ and as expressed in Xenopus oocytes. The oocyte expression system is useful for studies of the functional pharmacology of these 5-HTic receptors. Information about the pharmacological actions and variations in stereoselectivity among dopamine and 5-HT receptors should be of interest in modelling the interactions of ligands with these G-protein coupled receptors, and in the testing of such models through receptor mutagenesis.

Voltage dependence of Na/K pump current in Xenopus oocytes.

Stage V and VI (Dumont, J.N., 1972, J. Morphol. 136:153-180) oocytes of Xenopus laevis were treated with collagenase to remove follicular cells and were placed in K-free solution for 2 to 4 days to elevate internal [Na]. Na/K pump activity was studied by restoring the eggs to normal 3 mM K Barth's solution and measuring membrane current-voltage (I-V) relationships before and after the addition of 10 microM dihydroouabain (DHO) using a two-microelectrode voltage clamp. Two pulse protocols were used to measure membrane I-V relationships, both allowing membrane currents to be determined twice at each of a series of membrane potentials: (i) a down-up-down sequence of 5 mV, 1-sec stair steps and (ii) a similar sequence of 1-sec voltage pulses but with consecutive pulses separated by 4-sec recovery periods at the holding potential (-40 mV). The resulting membrane I-V relationships determined both before and during exposure to DHO showed significant hysteresis between the first and second current measurements at each voltage. DHO difference curves also usually showed hysteresis indicating that DHO caused a change in a component of current that varied with time. Since, by definition, the steady-state Na/K pump I-V relationship must be free of hysteresis, the presence of hysteresis in DHO difference I-V curves can be used as a criterion for excluding such data from consideration as a valie measure of the Na/K pump I-V relationship. DHO difference I-V relationships that did not show hysteresis were sigmoid functions of membrane potential when measured in normal (90 mM) external Na solution. The Na/K pump current magnitude saturated near 0 mV at a value of 1.0-1.5 microA cm-2, without evidence of negative slope conductance for potentials up to +55 mV. The Na/K pump current magnitude in Na-free external solution was approximately voltage independent. Since these forward-going Na/K pump I-V relationships do not show a region of negative slope over the voltage range -110 to +55 mV, it is not necessary to postulate the existence of more than one voltage-dependent step in the reaction cycle of the forward-going Na/K pump.

Effect of parenteral medications on tcPO2/PaO2 ratios.

We studied the effect of parenteral infusions on transcutaneous arterial oxygen tension ratios in 31 newborn rabbits. Tolazoline and prostaglandin E1 produced a significant fall in skin PO2 values (P less than 0.01). Antibiotics, bicarbonate, diazepam, and dopamine infusions produced no change in PO2 ratios.

Osmolality of carbohydrate solutions and gastric emptying in the newborn.

Gastric emptying in normal newborns was studied with use of a double marker technique. The volume of 200 to 400 mOsm carbohydrate solutions emptied from the stomach in 30 minutes was determined. To evaluate isocaloric solutions of different osmolalities, the osmolality of a 400-mOsm glucose solution was decreased to 300 and 200 mOsm/L by replacing a portion of the glucose with glucose oligosaccharides (GOSs). Because GOSs could be rapidly hydrolyzed in the duodenum, the effect of osmolality alone was studied by adding xylose to a 200-mOsm glucose solution to increase the osmolality to 300 and 400 mOsm/L. The volumes of the various solutions emptied in 30 minutes were not significantly different. These findings suggest that decreasing formula osmolality from 400 to 200 mOsm offers no intrinsic advantage with regard to gastric emptying.

Red blood cell volume in preterm neonates.

In the high-risk neonate, the direct determination of the red cell volume by radionuclide dilution technique appears to be the singularly definitive method of defining treatment efficacy, and is thus a useful evaluation and management tool for the pediatrician. For effective patient management, the red blood cell(RBC) volume of 69 preterm and term neonates was determined. The method utilized, Tc-99m-labeled RBCs, provided a fast and accurate answer with a large reduction in the absorbed radiation dose. In the population studied within a high-risk newborn ICU, the mean RBC volumes between the preterm and term neonates were without significant difference. Grouping and analysis of the RBC volume data with respect to birth weight, gestational ages, and 1- and 5-minute Apgar scores revealed on statistical difference. The mean value found in our population, 32.2 +/- 9.2 ml/kg, however, does differ from those previously reported in which the determinations were made using an indirect estimation from the plasma compartment.

Evaluation and testing of in vitro labeled technetium Tc-99m red blood cells in two animal models for neonatal RBC volume determinations.

The present study was designed to evaluate the red blood cell (RBC) radiolabeling technique utilizing the short half-lived radionuclide technetium-99m and to compare the results with the well-recognized standard chromium-51 method. The procedure was evaluated in a canine and a newborn lamb model utilizing dual radionuclide labeling and counting techniques. With the express purpose of providing a significant radiation dose reduction, the procedure presented was adapted for utilization in a neonatal patient population. Statistical analysis of the data revealed that there was no significant difference in the radiolabeling efficiency for the two methods (Cr-51, 86.6%; Tc-99m, 92.4%). Assessment of the in vitro stability for technetium-99m RBCs showed that less than a 4% loss of radiolabel from the RBC was seen in a 4-hr time span in the canine model (15 min, 90.5%; 2 hr, 88.9%; 4 hr, 86.6%) when compared to the 15 min equilibrium sample. Evaluation of newborn lamb RBC volumes showed that the technetium-99m RBC volume did not significantly differ from the chromium-51 labeling technique (Cr-51, 24.0 ml/kg; Tc-99m, 23.2 ml/kg). Summarization of the whole-body radiation dose showed that greater than a 30-fold reduction in absorbed dose was achieved in the newborn (Cr-51, 30.0 mrad; Tc-99m, 0.9 mrad). The modified procedure presented for the radiolabeling of the RBC with the short half-lived radionuclide technetium-99m provides a technique comparable to the utilized standard chromium-51 RBC method, yet with a large reduction in absorbed radiation dose. This procedure is presented as a superior technique for the determination of pediatric RBC volumes.

Collection and use of autologous fetal blood.

A prospective study was completed to evaluate the feasibility of autologous fetal blood collection. Following puncture on the umbilical vein, fetal blood was drawn into sterile heparinized plastic syringes and aliquots were subjected to coagulation and culture studies. None of the blood samples exhibited significant growth of bacterial pathogens and all patients had normal coagulation studies at 24 hours of age. These data demonstrate that fetal blood can be safely collected and given to infants subjected to shock or iatrogenic blood loss.

Manometric diagnosis of lower esophageal sphincter incompetence in infants: use of a small, single-lumen perfused catheter.

Lower esophageal sphincter (LES) pressure is frequently measured to diagnose LES incompetence in adults. The multilumen perfused catheters with large diameters that are used for ths purpose are not suitable for small infants. We measured LES pressure in ten normal newborns with a small, single-lumen perfused catheter and compared our values with those obtained with the standard adult apparatus. Higher pressures were recorded with the single-lumen catheter. Chloral hydrate sedation had no effect on LES pressure. Two-day-old infants had LES pressures comparable to those of adults and older children. The technique was applied to the diagnosis of LES incompetence in 23 infants. Infants with LES incompetence (chalasia) were correctly separated from infants with chronic vomiting secondary to all other causes. Single-lumen manometric studies provide a simple, reliable, and safe method of assessing LES incompetence in small infants.

Effect of uterine artery insulin infusions on umbilical glucose uptake in sheep.

Although glucose is an important fuel for fetal oxidative metabolism, regulation of its availability to the mammalian fetus is poorly understood. This study was performed to determine the effect of infusions of insulin into the uterine arterial circulation on umbilical uptake of glucose in chronically instrumented, unstressed sheep. Twenty-eight determinations of umbilical glucose uptake and diffusion clearance of glucose by the placenta were made in four ewes. Immediately following a control study during which saline was infused into the uterine artery, porcine regular insulin diluted in saline was infused at 0.05 to 8.1 mU/min . kg uterine weight for 20--30 min and the determinations were repeated. Subsequent studies were performed at the conclusion of additional infusions of insulin to a maximum of 21.6 mU/min . kg. There was a significant increase in umbilical glucose uptake during initial insulin infusions (4.47 +/- 0.6 mg/min . kg fetus) compared to the control studies (3.08 +/- 0.6 mg/min . kg) associated with an increase in diffusion clearance (13.8 +/- 1.9 ml/min . kg fetus vs. 8.99 +/- 1.8 ml/min . kg). When the total cumulative dose of exogenous insulin, It, was 162 mU/kg uterine weight or less, the umbilical uptake of glucose, Q, may be expressed as a function of maternal arterial blood glucose concentration in milligrams per dl, [A], and of It.

Neonatal shock in the first postnatal day.

Advances in neonatal medicine have markedly reduced mortality in preterm infants. Current emphasis should be placed on early detection and treatment of neonatal hypotension and shock. Ideal clinical management includes perinatal recognition of low birth weight infants at risk for hypotension. All critically ill preterm infants should be closely monitored for tachycardia, hypotension, and/or decreased urinary output. By use of noninvasive blood pressure screening techniques, hypotensive infants may be identified in the first hours of life. Judicious use of whole blood or balanced salt solutions will result in reduction of mortality from 50% to 10%.

Congenital torsion of the penis in father-son pairs.

Congenital torsion of the penis was observed in 5 newborns, 3 of whom had fathers with torsion of the penis. We believe that this common benign condition may be transmitted as an autosomal dominant trait.

Syndrome of inappropriate antidiuretic hormone secretion in neonates with pneumothorax or atelectasis.

Nine episodes of the syndrome of inappropriate antidiuretic hormone secretion occurred in five newborn infants following atelectasis or pneumothorax. All infants had pre-existing lung disease and were being treated with positive pressure ventilation. The mean interval between acute atelectasis or pneumothorax and the development of diagnostic hyponatremia, hypo-osmolal serum, hyperosmolal urine, and oliguria was 13.4 hours. Fluid restriction and removal of the triggering event resulted in resolution of the abnormalities within 1.5 to 4 days. Infants who develop atelectasis or pneumothorax should be evaluated for the subsequent occurrence of SIADH; the administration of a water load to them may result in dilutional hyponatremia, for which fluid restriction, not sodium infusion, is the proper therapy.

Osmolalities of infant formulas.

The osmolalities of breast milk and of 36 products that may be fed to infants were determined by the freezing-point depression method. A wide range of osmolality was observed among formulas that provide 67 kcal/100 ml, and many have osmolalities greater than 400 mOsm/kg of water. Reconstituted powdered formulas have osmolalities that are widely varied from batch to batch, are greater when prepared by scoop measures when the osmolalities of corresponding ready-to-feed formulas, and are greater than the osmolalities of the formulas prepared by weighed measures from the manufacturer's formulation. The osmolality of products for oral consumption should be considered in the selection of formulas for preterm infants.

Post-traumatic anterior hypopituitarism.

Reports of anterior pituitary insufficiency following closed head trauma are unusual. In those cases reported, extensive endocrinologic evidence to support the clinical syndrome is often lacking. The present report documents a case of anterior pituitary insufficiency in a 14-year-old girl following a skull fracture. Endocrine evaluation one year after her automobile accident revealed hypopituitarism minifested by cachexia, hypothyroidism, hypoadrenocorticism, and hypogonadism with regression of secondary sex characteristics. Laboratory studies demonstrated deficiencies of both trophic and peripheral anterior pituitary hormones. The patient has responded to replacement therapy and is clinically well. A review of previously described cases is included.

Hemodialysis in an infant with propoxyphene intoxication.

A 10-month-old infant was treated with intensive supportive care and hemodialysis for severe propoxyphene intoxication. Dialysis clearance studies demonstrated that propoxyphene was removed from the serum at approximately 50% of the rate of blood urea nitrogen removal. Possibly because of tissue binding of the drug, the absolute quantity of propoxyphene removed by dialysis was small. The child survived the acute episode of intoxication but died of pulmonary complications several days later. The role of dialysis in propoxyphene intoxication remains to be established.