James M. Norton

Evidence for Direct Control of Coronary Vascular Tone by Oxygen

The interaction between the effects of oxygen and adenosine on acetylcholine-induced contractile tension was observed in helical coronary arterial strips suspended in physiological salt solution. It was found that (1) steady-state contractile tension was unaffected or depressed 5–20% when oxygen pressure (Po2) was diminished to levels as low as 5–10 mm Hg, (2) contractile tension was markedly depressed at a Po2 of 0 mm Hg, (3) adenosine-induced relaxation of contractile tension was inversely proportional to Po2 in the tissue bath, and (4) in the presence of adenosine at a concentration just adequate to inhibit contractile tension at a Po2 of 10 mm Hg, contractile tension was directly proportional to bath Po2. The latter two observations were usually most apparent at a Po2 between 10 and 40 mm Hg. It is proposed that the vasodilating effect of adenosine on the intact coronary vasculature may be most effective during myocardial hypoxia and that physiological control of coronary vascular tone may be more closely related to variations in local Po2 than to variations in local concentrations of adenosine.

Dose-related effects of the sex hormones and cortisol on the growth of the bursa of fabricius in chick embryos

Abstract The administration of a single dose of either testosterone propionate progesterone, estradiol, or cortisol in vivo to developing chick embryos on the fifth day of incubation significantly alters the size of the bursa of Fabricius measured on day 19. Depending on dose, testosterone propionate or progesterone can have either stimulatory or inhibitory effects on bursal growth. When low doses were administered (0.02–2.0 μg), comparable to what the chick embryo might be exposed to during development, both hormones were stimulatory; at higher levels (20–2000 μg), both either partially or entirely inhibited bursal growth. In contrast, estradiol and cortisol were found to have no stimulatory effects at low levels, but markedly inhibited bursal growth at higher concentrations (20–2000 μg/egg). The results of this study suggest that the steroid hormones play an important role in the growth of the bursa of Fabricius in developing chick embryos. This phenomenon may have bearing on subsequent immunelogical responsiveness.

Effects of adenosine on isolated coronary vascular smooth muscle

SummaryThe effect of adenosine on contractile tension was investigated in helical strips taken from free-wall left ventricular coronary arteries freshly excised from rabbit hearts. Strips were cut from large and small segments of the same artery and suspended in PSS at pH 7.4, PO2 100 mm Hg and 37°. Adenosine, 0.1 μM or less, usually had little or no effect on steady-state drug-induced contractile tension while 1 μM adenosine produced moderate relaxation. Adenosine, at concentrations as low as 0.1 μM, blocked, or reduced the rate of tension development especially in strips from the smaller vessel segments. Adenosine was approximately as effective, on a molar basis, as norepinephrine and isoproterenol, but less effective than nitroglycerin in relaxing contractile tension.It is concluded that adenosine is moderately potent in relaxing steady-state contractile tension of helical strips taken from both large and small coronary vasculature of the rabbit.