Artificial feeding and hospitalization in the first 18 months of life

The association between type of feeding and hospitalization during the first 18 months of life was examined among 1,058 infants from Jing-An district, Shanghai, People's Republic of China. Infants who had never been fed with mother's milk were categorized as artificially fed; the remainder were breast-fed. The rate of hospitalization for first episodes of respiratory infections during the first 18 months of life for the artificially fed infants was 18.0% v 11.2% for the breast-fed infants (P less than .01). Multiple logistic regression analysis demonstrated that the adverse effect of artificial feeding on the hospitalization rate for respiratory infections was independent of birth weight, father's education, passive smoking, and any case(s) of chronic respiratory disease in the family. The adjusted odds ratio for the artificially fed infants compared with the breast-fed infants was 2.11. The artificially fed infants were also hospitalized more frequently for gastroenteritis and other conditions, but the differences were not significant.

Comparison of albumin and casein microspheres as a carrier for doxorubicin

Doxorubicin (Adriamycin)-loaded casein and albumin microspheres, with diameters between 14 and 38 micron (50% weight average) were prepared by glutaraldehyde stabilization of the aqueous phase (containing protein and drug) of a water in oil emulsion. Physical properties, drug loading characteristics and release rates from microspheres in-vitro have been compared and correlated with effects on tumour growth when injected intratumourally in rats. Compared with albumin, the surface charge of the casein system was more negative and the microspheres exhibited a slower release of drug in-vitro. Both observations could be explained by the lower drug content of the casein system. There was evidence for the formation of a doxorubicin complex in the microspheres, the significance of which is not yet known. Casein microspheres containing 11 micrograms of doxorubicin had a similar inhibitory effect on tumour growth (growth delay = 20.7 days) to 85 micrograms of drug incorporated into albumin microspheres (growth delay = 18.6 days). The absence of a simple dose-response relationship shows that carrier matrix can influence potency of incorporated drug. The results are consistent with release rate of the drug from microspheres (obversely, rate of drug delivery to the tumour), being a determinant of potency in these systems.

Unexpected responses of the hypothalamic gonadotropin-releasing hormone "pulse generator" to physiological estradiol inputs in the absence of the ovary

In the rhesus monkey (Macaca mulatta), the frequency of pulsatile gonadotropic hormone release is relatively constant in the face of widely varying levels of estradiol (E2) in the peripheral circulation--e.g., in the course of the follicular phase of the menstrual cycle and after ovariectomy. This suggests that modulation of the hypothalamic gonadotropin-releasing hormone (GnRH) "pulse generator" by this steroid is not of major physiological importance. Herein is described the unexpected inhibition or total blockade of the electrical activity of this pulse generator in ovariectomized monkeys by physiological levels of exogenous E2. This inhibition began 2-4.5 hr after the initiation of E2 infusion and was noted 1 to 3 weeks after subcutaneous implantation of E2-containing capsules. Pulse generator activity was also arrested during the initiation and subsequent development of estrogen-induced surges of luteinizing hormone. We propose that this inhibition of hypothalamic GnRH pulse generator activity by E2 in ovariectomized monkeys reflects the absence of an ovarian factor that normally protects this neuronal system from the inhibitory action of estrogen during the menstrual cycle.

Free energy transduction in membrane transport systems induced by externally imposed fluctuations in ligand concentrations

The effect of externally induced fluctuations in ligand concentration on the transport of ligand across a membrane is studied theoretically. It is found that, when only one of the two baths is externally perturbed to fluctuate the concentration, a net transport of ligand from the unperturbed to the perturbed side of the membrane is always observed, even though the average concentrations of ligand of the two baths are equal. As a result, apparent up-hill transport against a gradient can be realized in this case. In the case of both baths being perturbed independently, apparent up-hill transport is also possible. However, the direction of net transport of ligand will depend on the amplitudes and the frequencies of the two fluctuations as well as the kinetic mechanism of the transport system. From these results, it is concluded that externally imposed fluctuations in ligand concentration act to reduce the chemical potential of the ligand so that the effective activity is always less than the mean concentration of the ligand. The conclusion is very general in that it applies to any transport model that involves one ligand per turnover. The same principle can be used to analyze the effect of fluctuations in equilibrium ligand binding and cyclic enzyme reactions in solution.

Synchronous oscillations in microtubule polymerization

Under conditions where microtubule nucleation and growth are fast (i.e., high magnesium ion and tubulin concentrations and absence of glycerol), microtubule assembly in vitro exhibits an oscillatory regime preceding the establishment of steady state. The amplitude of the oscillations can represent greater than 50% of the maximum turbidity change and oscillations persist for up to 20 periods of 80 s each. Oscillations are accompanied by extensive length redistribution of microtubules. Preliminary work suggests that the oscillatory kinetics can be simulated using a model in which many microtubules undergo synchronous transitions between growing and rapidly depolymerizing phases, complicated by the kinetically limiting rate of nucleotide exchange on free tubulin.

Binding of n-mers to one-dimensional lattices with longer than close-contact interactions

A general formalism is derived for the evaluation of binding isotherms of n-mers (ligands) to one-dimensional polymers in the presence of ligand-ligand interactions which extend over several binding sites with distance-dependent interaction energies (multi-parameter model). This is an extension of the usual n-mer binding theory developed by several investigators in which ligand-ligand interaction occurs only when two ligands are in close contact (one-parameter model). The difference in binding isotherms between a one-parameter model and a multi-parameter model is studied numerically using the present formalism.

Anisotropic fiber with a depressed-cladding profile

Anisotropic fibers of the depressed-cladding type are analyzed by employing an iterative perturbation technique in a simple and straightforward way. An analytic expression is obtained for calculating the leaky-mode losses of an anisotropic depressed-cladding fiber. Numerical results show that such fibers possess much higher losses than those predicted earlier for a step-index model and hence are more advantageous for use in achieving singlepolarization, single-mode operation.