Donald E Hill

Skeletal Muscle Cell Mass and Growth: The Concept of the Deoxyribonucleic Acid Unit

Speculation: Two important predictions, contradicting current opinion, arise from his review:Removal of the pituitary causes loss of muscle deoxyribonucleic acid (DNA) in the weanling rat. Exercise causes increase in muscle tissue with a commensurate increase in DNA and protein. Therefore, some of the muscle DNA must be in a dynamic state.Calorie restriction (without protein restriction) imposed during the postweanling period of growth in rats does slow cell multiplication but does not cause permanent growth retardation. Therefore, protein restriction, per se, is probably responsible for permanent growth retardation in the experimental animal.

Malnutrition in Infancy: Changes in Muscle and Adipose Tissue Before and After Rehabilitation

Extract: In nine infants suffering from protein-calorie malnutrition, significantly low values for muscle mass and cell mass which were proportional were observed. These were 1.02±0.44 kg and 2,295±693 pg, respectively (P < 0.001). The extracellular volume was disproportionally high relative to creatinine excretion before and after rehabilitation. The extracellular volume was disproportionally high relative to creatinine excretion before and after rehabilitation. The major loss of muscle mass was due to loss of cell size rather than cell number.The protein/DNA ratio was 78±18.7 (P<0.001) prior to rehabilitation and 109.6±45.1 (P<0.001) following rehabilitation. The RNA/DNA ratio was low at 0.96±0.26 (P0.001) prior to rehabilitation while after rehabilitation the value increased to 1.24±0.14 but was still less than normal (P<0.01).The levels of Mg and Zn per unit DNA were reduced in muscle prior to rehabilitation. These values were 6.6±0.7 and 35.6±15.8, respectively (P<0.001).The significantly reduced protein/DNA and RNA/DNA ratios after rehabilitation suggest either persistent alteration in mechanisms responsible for protein synthesis or a prolonged period necessary for recovery. Muscle mass of 1.67±0.64 kg was not significantly different from the normal for body length after rehabilitation.The concerntrations of water (39.96±16.99) and collagen (3.86±2.24) in adipose tissue were elevated (P<0.01), while that of fat (50.36±21.87) was low prior to rehabilitation. The noncollagen protein was constant per gram of tissue in marasmus and following rehabilitation.Speculation: Because insulin is intimately related to protein synthesis and the attainment of normall cytoplasmic growth, the persistently poor secretion of insulin during rehabilitation from malnutrition may be responsible for inadequate cytoplasmic growth.Inaulin administered judiciously during the recovery phase may accelerate recovery and insure a return to normal.

125I-Insulin Receptor Binding to Cord Blood Erythrocytes of Varying Gestational Age and Comparison with Adult Values

Summary: The measurement of 125I-insulin binding to erythrocytes from 34 samples of cord blood (% B/T = 11.2 ± 3.8) showed statistically significant differences when compared to adult erythrocytes (% B/T = 6.6 ± 1.7). Preterm erythrocytes (% B/T = 14.7 ± 3.4) bound significantly more insulin when compared to term erythrocytes (% B/T = 10.1 ± 3.2). The negative correlation (r = −0.613; P = 0.001) between insulin binding and gestational age indicates that the trend during the final trimester of gestation is toward the lower binding observed for adult cells.The major differences in binding between adult and term cord blood erythrocytes may be primarily attributed to differences in the number of binding sites per cell. Additionally, there are small differences in both affinity and number of sites per cell in preterm as compared to term and adult erythrocytes.Speculation: The mechanisms governing insulin release from the pancreas are not mature in utero. Insulin released directly into the circulation from the fetal pancreas may be bound to tissue receptors in relation to the affinity and concentration of specific surface receptors, thereby, providing direct control at the cellular level for rapidly growing fetal tissues. Erythrocyte receptors may serve to transport insulin for this purpose.

Cardiovascular and renal effects of dopamine and dobutamine in healthy, conscious piglets

The pharmacologic effects of dopamine and dobutamine (2 to 32 micrograms/kg.min) were evaluated in 12 1 to 2-month-old piglets. Dopamine increased cardiac output at 16 to 32 micrograms/kg.min (p less than .05) and increased heart rate (HR) at 4 to 32 micrograms/kg.min (p less than .05). Dobutamine produced an increased cardiac output at doses of 16 to 32 micrograms/kg.min (p less than .05), and increased HR at 32 micrograms/kg.min (p less than .05), decreased systemic arterial pressure and systemic vascular resistance at 16 to 32 micrograms/kg.min (p less than .05), decreased renal vascular resistance at 16 to 32 micrograms/kg.min, and increased renal blood flow at 4.8 and 32 micrograms/kg.min (p less than .05). We conclude that dopamine and dobutamine increase cardiac output in healthy, conscious piglets primarily by increasing HR. Neither agent was effective in increasing stroke volume, although a positive inotropic effect obscured by tachycardia cannot be ruled out. Dobutamine was the superior agent for renal vasodilation, whereas neither agent produced significant pulmonary vasodilation.

A NEW SYNDROME OF FAMILIAL PANCREATIC AGENESIS: THE ROLE OF INSULIN AND GLUCAGON IN SOMATIC AND CELL GROWTH

Two sibs of a consanguineous union were born with severe intrauterine growth retardation and agenesis of the pancreas confirmed at autopsy. We report the association between the growth failure and absence of fetal insulin and glucagon, and some of the changes in somatic and cell growth occurring in one of the infants at age 6 weeks. Birth weight 1280 gm at term; length 37 cm; head circ. 29 cm; (all <3rd centile). The brain weighed 214 gm (<3rd centile), and the liver weighed 95.7 gm (<25th centile). All other visceral organs were extremely small, particularly the adrenals whose combined weight of 1 gm was less than that of a 24-week old fetus. The total DNA in the cerebrum was 172 mg (N=258), in the cerebellum 95.6 mg (N=120), and in the liver 200 mg (N=320), respectively, indicating a reduction in the cell number in each of these organs. Protein/DNA ratio was normal or increased in brain and liver indicating a relatively greater reduction in DNA content than in protein. In muscle, the total DNA was reduced as calculated from muscle mass and the protein/DNA ratio of 58 was extremely low (N=100). The results in brain and muscle were similar to those seen in infants with severe postnatal marasmus, and suggest that insulin and glucagon are key hormones for normal fetal growth.

Glucose homeostasis in preterm rhesus monkey neonates.

Summary: Response to a primed glucose infusion (0.5 g/kg injected over 3 min and 8 mg/kg/min infused for 3 hr) was studied in 5 term and 11 preterm rhesus monkey neonates 2–3 hr after delivery by cesarian section. The glucose challenge perturbed a steady state glucose specific activity achieved in the previous 100 min by a primed trace infusion of 2-[3H]glucose (6 μCi and 0.2 μCi/min). This allowed the determination of changes in endogenous glucose turnover in response to exogenous glucose in the immediate newborn period.With glucose challenge, the 5 term animals and 6 of the 11 preterm animals developed a new steady state glucose concentration (80–100 ml/dl). Coincident with this was a marked reduction in endogenous hepatic glucose output and a moderate increase in peripheral glucose utilization as measured by the tracer methodology. In contrast, the other five preterm monkeys developed hyperglycemia upon glucose challenge (190–210 mg/ dl). All groups had similar glucose-stimulated insulin release which peaked after 60 min of glucose infusion. However, in comparison to the other groups, the group that was to develop hyperglycemia exhibited: (1) lower basal insulin and higher basal glucose values; (2) no suppression of endogenous hepatic glucose output or lipolysis despite glucose-stimulated insulin release; (3) lower birth weight and gestational age, and increased eventual mortality. Hypoxia was not evident in any group as evidenced by clinical signs and decreasing lactate/ pyruvate ratios during the glucose infusions.Speculation: The inability of certain preterm rhesus monkeys to maintain normoglycaemia, but rather to develop hyperglycemia in the face of a glucose infusion might be related to inappropriate adrenergic activity unrelated to cither hypoxia or hypothermic stress. This represents an animal model for the further study of hyperglycemia seen in certain human preterm neonates.

Cromolyn Sodium Decreases the Pulmonary Vascular Response to Alveolar Hypoxia in Lambs

ABSTRACT. We investigated the effect of cromolyn sodium, a mast cell stabilizing agent, on the pulmonary vascular response to alveolar hypoxia in six chronically instrumented lambs aged 9 to 11 days. Each lamb was instrumented on day 6 or 7 for measurements of systemic arterial, pulmonary arterial and left atrial pressures, and pulmonary blood flow. The animals were allowed to recover from surgery at least 3 days before they were studied. Each animal was studied twice, once with a cromolyn sodium infusion and once with a normal saline infusion (placebo). These paired experiments were separated by 24 h. Physiologic measurements were made during a 1-min predose control period, after an 8-min drug or placebo infusion, and after a 15-min period of alveolar hypoxia. Cromolyn sodium infusion alone did not affect baseline cardiovascular variables. Alveolar hypoxia following placebo infusion produced an increase in pulmonary arterial pressure and pulmonary vascular resistance; these responses were blocked in the animals given cromolyn sodium prior to induction of hypoxia. These results show that cromolyn sodium blocks the pulmonary vascular response to hypoxia and provide indirect evidence that mast cell degranulation, with subsequent release of vasoactive agents, mediates the pulmonary vascular response to hypoxia in newborn lambs.

The Noncollagen Protein in Adipose Tissue as an Index of Cell Number

Summary Adipose tissue biopsies from infants and children ranging in age from 6 months to 17 years were examined. The composition of the adipose tissue was determined and the percentage of noncollagen protein computed. Duplicate adipose tissue samples were used for fat cell number determinations according to the method of Hirsch and Gallian (3). A highly significant (p < .001) positive correlation was found between the percentage of noncollagen protein (NCP) and the cell number per gram of tissue. This correlation may be improved by direct measurement of isolated fat cell protein. The regression equation can be an aid in prediction of total body fat cell number when body fat is known. The authors gratefully acknowledge the surgical assistance of Dr. G. N. Peters and J. J. White, and the technical assistance of Miss Rachel Scott and Mrs. E. Higginbottom.

Theophylline and caffeine disposition in the neonatal piglet

A pharmacokinetic study to evaluate the piglet as a model for caffeine and theophylline disposition was undertaken in 28 animals who received a 10.0-mg/kg intravenous dose of either methylxanthine, followed by multiple blood sampling over a 24-hour period. Theophylline and caffeine concentrations were quantitated from serum using a microanalytical HPLC technique (coefficient of variability less than 7% at 0.1-100 mg/l). The influence of postnatal development on drug disposition was examined by dividing the experimental animals into three age groups (newborn, 2 days; perinatal, 4-5 days; infants or young, 15-22 days). Pharmacokinetic parameters were calculated from nonlinear curve fitting of serum concentration vs time data. On the basis of the terminal elimination rate constant (lambda z) and total clearance (CL) for both theophylline and caffeine, differences were found among the age groups. The apparent volume of distribution (Vz) for both methylxanthines was not found to be different when compared between age groups. Covariance determinations between age and pharmacokinetic parameters revealed linear correlations for Vz of caffeine and CL for both theophylline and caffeine. In all piglets receiving theophylline, no caffeine was detected in serum during a 24 hr period. Theophylline, however, was detected (0.4 +/- 0.2 mg/l at 11.5 hr) in the four oldest piglets who received caffeine. Similarities between pharmacokinetic parameters for caffeine and theophylline reported for human neonates were found only for newborn piglets. Furthermore, the biotransformation of theophylline to caffeine reported for human neonates was not observed in neonatal piglets.

Reduced insulin binding in a large kindred with severe diabetic retinopathy

Specific insulin binding to erythrocyte receptors (IRB) has previously been reported to be unaltered in children and adolescents with insulin dependent diabetes mellitus (Ped. 66:385, 1980). However, we report here that five insulin dependent, ketosis-resistant juvenile diabetics from the same kinship have a significant reduction in the percent IRB (normal 8.32±2.71 vs 4.72±0.84 for the diabetic children). Three non-diabetic juveniles in the family have an intermediate value of 5.77±1.08. The youngest child shows normal binding. Scatchard analysis of the high and low affinity insulin binding sites indicates that the reduced IRB is due to a decrease in the number of receptor sites per cell. There is no correlation with circulating plasma insulin values nor with the severity of diabetes. However, the insulin dependent diabetics have an inordinate degree of ocular and vascular complications for the severity of their diabetes. Human lymphocyte antigens A, B, C, and D as well as islet cell antibodies are being determined in all family members to correlate with IRB data. Since diabetes mellitus is a heterogeneous disorder, we postulate that abnormal IRB in these patients may be genetically determined and related etiologically to their severe microangiopathy (retinopathy).