Radioimmunoassay of human plasma corticosterone: method, measurement of episodic secretion and adrenal suppression and stimulation

A radioimmunoassay for human plasma corticosterone has been developed. Antisera were obtained by immunizing rabbits with corticosterone-21-hemisuccinate-BSA. An antiserum titer of 1:4000 was used for standard curves ranging from 0–1000 pg. Interfering steroids were removed from plasma extracts by paper chromatography. Plasma blanks obtained from adrenalectomized or Addisonian patients ranged from 29 to 42 ng/dl. Recovery of radioactive corticosterone through the entire method was 67.6 ± 5.2%. The coefficient of variation within assays was 19% and between assays 13%. The average 8 a.m. value in males was 396 ± 228 ng/dl and in females it was 655 ± 271 ng/dl. Corticosterone was found to be secreted episodically, in parallel with cortisol. Secretion of this steroid was suppressed by dexamethasone and stimulated by ACTH infusion.     

Inhibitors from Carob (Ceratonia siliqua L.) I. Nature of the Interaction With Gibberellic Acid on Shoot Growth

Concentrated whole extracts of the immature fruit of carob and 3 fractions derived from this extract have been shown to inhibit the gibberellic acid induced growth of pea seedlings. The inhibition can be completely reversed by increasing the amount of gibberellic acid. The inhibitors do not reduce the endogenous growth of seedlings but only that induced by gibberellic acid. One of the fractions is a newly separated one not previously reported.     

Effect of Temperature on the Potential and Current Thresholds of Axon Membrane

The effect of temperature on the potential and current thresholds of the squid giant axon membrane was measured with gross external electrodes. A central segment of the axon, 0.8 mm long and in sea water, was isolated by flowing low conductance, isoosmotic sucrose solution on each side; both ends were depolarized in isoosmotic KCl. Measured biphasic square wave currents at five cycles per second were applied between one end of the nerve and the membrane of the central segment. The membrane potential was recorded between the central sea water and the other depolarized end. The recorded potentials are developed only across the membrane impedance. Threshold current values ranged from 3.2 µa at 267deg;C to 1 µa at 7.5°C. Threshold potential values ranged from 50 mv at 26°C to 6 mv at 7.5°C. The mean Q₁₀ of threshold current was 2.3 (SD = 0.2), while the Q₁₀ for threshold potentials was 2.0 (SD = 0.1).