Pineal N-acetyltransferase depression in rats exposed to heat

Summary Exposure of adult male rats to increased temperature of 33±1°C for 3 and 10 days brought about decreases in pineal N-acetyltransferase activity. These and previous findings of pineal HIOMT inhibition under similar conditions support the postulation of a possible thermoregulatory role for the pineal gland.     

Why do patients with respiratory muscle paralysis require artificial hyperventilation?

The primary reason for the need of hyperventilation in patients with respiratory paralysis is the insufficiency of the inhibitory Hering-Breuer reflex. The artificial distension of the lungs with normal tidal volume cannot inhibit the respiratory centre in contrast to the normal state.     

HCO 3 − -ATPase activity distribution in rat liver cell fractions prepared by zonal centrifugation

Summary Plasma membrane sheets prepared by zonal centrifugation of a premicrosomal pellet obtained from a rat liver homogenate are devoid of HCO ₃ ^– -ATPase activity. Since the microsomal fraction is also lacking in this ATPase activity, it can be concluded that the HCO ₃ ^– -ATPase is not involved in the secretion of HCO ₃ ^– into bile. Acknowledgments. This investigation was supported in part by grants No. DE-02600 and AM 80686 from the United States Public Health Service. The A-XII zonal rotor is used under subcontract No. 3796 with the Union Carbide Corporation.     

Spatial distribution of the adaptation field of the surround response mechanism in type X cat retinal ganglion cells

Summary The surround response mechanism in on-center X-cells in cat retina was found to be bimodally distributed and weak or nonexistent in the receptive field middle. An on-inhibition measure was used to assess surround mechanism gain.Acknowledgments. This research is supported by Public Health Service grant No. EY 00701.     

Serum cholesterol levels in a Nigerian population sample

Serum cholesterol was determined in 104 healthy Nigerians (57 males and 47 females). The average cholesterol concentration was 187 +/- 72.8 mg/100 ml (mean +/- SD) with a range of 60-480 mg/100 ml. Cholesterol levels were higher in males than in females and increased with age. Distribution of cholesterol level was generally skew to the left.     

A comment on the design of experiments to estimate the Michaelis-Menten parameters of enzyme-catalysed reactions

Summary Michaelis-Menten parameters can be estimated by measuring initial velocities (v) in replicate at 2 concentrations of substrate, one much lower than K_m and the other much higher than it. Analysis of simulated experimental data suggests that this design will probably give more precise estimates of K_m and V than the conventional design in which v is measured at several different concentrations of substrate.     

Comparison of bicyclic phosphorous esters with bicuculline and picrotoxin as antagonists of presynaptic inhibition in the rat cuneate nucleus

Summary The effects of 2 of a series of bicyclic phosphorous esters, the ethyl (EPTBO) and isopropyl (IPTBO) compounds, were compared with those of the GABA antagonists, picrotoxin and bicuculline, on presynaptic inhibition in the rat cuneate nucleus. Both EPTBO and IPTBO were found to be effective, reversible antagonists of presynaptic inhibition, with IPTBO approximately 10 times more potent than EPTBO and equipotent with bicuculline, EPTBO equipotent with picrotoxin.The authors are grateful to Dr J. F. Collins, Department of Chemistry, Sir John Cass School of Science and Technology, 31 Jewry Street, London, for the gift of bicyclic phosphorous esters.     

Regulation of mouse trophoblast giant cell nucleus development in hatched mouse blastocysts by cyclic cytidine 3′,5′-monophosphate (cCMP)

Summary The dibutyryl analog of cCMP enlarged the nuclei of trophoblast gian cells and promoted blastocyst development. The result suggests that cCMP has a trophic effect on embryonic development, specifically by altering the size of the trophoblast cell nucleus but does not enhance trophoblast cell proliferation processes.     

Effect of phosphorylation of myosin light chains on interaction of heavy meromyosin with regulated F-actin in ghost fibers

The binding of phosphorylated heavy meromyosin to regulated F-actin in ghost fibers at high Ca2+ concentration increases, and at low Ca2+ concentration decreases, the anisotropy of intrinsic tryptophan fluorescence of F-actin. The effect is opposite to the effect of the binding of dephosphorylated heavy meromyosin.