Transport of beta-hydroxybutyrate (betaHB) into rat brain was estimated from the early rise in brain/serum 14C ratio after subcutaneous injection of [14C]betaHB. Permeability of the D isomer exceeded that of the L isomer. Permeability of either isomer rose throughout suckling (sevenfold) and declined after weaning to the low, newborn values. This age dependence differed markedly from those of cerebral blood flow and cerebral permeabilities of urea, glucose, valine, leucine, and DMO (5,5-dimethyloxazolidine-2,4-dione). Fat-feeding more than doubled cerebral betaHB permeability without significantly affecting cerebral blood flow or the permeabilities of urea, glucose, and DMO. Temperature dependence of betaHB permeability was similar to that of glucose transport. The age and diet dependence of betaHB were not accounted for in terms of body temperature, capillary surface, capillary porosity, or plasma proton concentration. A modulable betaHB carrier seemed indicated. Utilization of betaHB by the brain was signficantly governed by permeability, hence the increased permeability in ketotoc states should contribute to glucose sparing and eventually to protein sparing.

The APS Journal Legacy Content is the corpus of 100 years of historical scientific research from the American Physiological Society research journals. This package goes back to the first issue of each of the APS journals including the American Journal of Physiology, first published in 1898. The full text scanned images of the printed pages are easily searchable. Downloads quickly in PDF format.

The APS Journal Legacy Content is the corpus of 100 years of historical scientific research from the American Physiological Society research journals. This package goes back to the first issue of each of the APS journals including the American Journal of Physiology, first published in 1898. The full text scanned images of the printed pages are easily searchable. Downloads quickly in PDF format.

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The peak pressure which a chamber would develop in isovolumic contraction at end-diastolic distention (peak source pressure) is an expression of contractile vigor and a determinant of systolic performance. One can predict source pressure of an ejecting beat by fitting its isovolumic phases with a model isovolumic-wave function. Characteristics of the left-ventricular isovolumic pressure wave (amplitude, duration, shape) were studied in isolated, perfused, artificially loaded dog hearts, where strictly isovolumic conditions could be obtained over a wide range of cavity volumes at constant heart rate and approximately constant contractile state. The characterization involved two steps: (1) beginning and ending points were identified by a transition-locating algorithm, and (2) Fourier analysis was performed on points in between. The amplitude of the isovolumic pressure wave increased with cavity volume as expected, the duration of contraction increased with cavity volume, and the shape of the wave (normalized Fourier coefficients) depended slightly on the cavity volume. Duration of contraction declined slightly with increasing heart rate, but the shape of the isovolumic pressure wave was independent of heart rate. The mean shape was similar to that found in dog hearts subjected to one-beat aortic-root clamping in vivo-the wave being less sharply peaked than a cosine wave and tilted to the left because relaxation was slower than contraction. When ejecting beat duration declined linearly with increasing ejection fraction. This relation could be used to predict the duration of the isovolumic beat corresponding to the duration of an ejecting beat. Source pressure could then be predicted by fitting a model isovolumic wave of predicted duration to the isovolumic contraction phase of the ejecting beat. In 270 comparisons, the ratio of predicted peak source pressure to observed peak source pressure was 1.04 +/- 0.10 (SD). This method provides a reasonably accurate prediction of an important determinant of systolic performance.