In vitro assessment of the selectivities of various beta-adrenergic blocking agents

Intrinsic sympathomimetic- and membrane activities of beta-adrenoceptor blocking agents are of little or no clinical significance. A selective blockade of cardiac receptors has important therapeutic consequences, especially in the treatment of patients with obstructive airways diseases. Profound depression of miocardial contractility can be deleterious in patients with cardiac muscle damage and the use of beta-adrenergic blockers with a quantitative selectivity towards chronotropism may become an important consideration. The effects of a number of beta-sympatholytics have been determined on isolated cardiac preparations (beta₁-adrenergic receptors) and tracheal preparations (beta₂-adrenergic receptors) of guinea-pigs. Results indicate that prindolol is the most selective blocker of the beta₁ chronotropic receptors whilst atenolol could be classified as being the most cardioselective beta-adrenergic blocker investigated. Butoxamine, on the other hand, proved to be the most beta₂-selective one.     

Heat exchanges in wet suits

Flow of water under foam neoprene wet suits could halve insulation that the suits provided, even at rest in cold water. On the trunk conductance of this flow was approximately 6.6 at rest and 11.4 W . m-2 . C-1 exercising; on the limbs, it was only 3.4 at rest and 5.8 W . m-2 . degrees C-1 exercising; but during vasoconstriction in the cold, skin temperatures on distal parts of limbs were lower than were those of the trunk, allowing adequate metabolic responses. In warm water, minor postural changes and movement made flow under suits much higher, approximately 60 on trunk and 30 W . m-2 . degrees C-1 on limbs, both at rest and at work. These changes in flow allowed for a wide range of water temperatures at which people could stabilize body temperature in any given suit, neither overheating when exercising nor cooling below 35 degrees C when still. Even thin people with 4- or 7- mm suits covering the whole body could stabilize their body temperatures in water near 10 degrees C in spite of cold vasodilatation. Equations to predict limits of water temperature for stability with various suits and fat thicknesses are given.