The relation between chemical constitution and physiological action : a lecture delivered before the Chemical Society on December 6th., 11917 / by Frank Lee Pyman.

  • Pyman, Frank Lee.
Date:
1917.]
Catalogue details

Licence: Public Domain Mark

Credit: The relation between chemical constitution and physiological action : a lecture delivered before the Chemical Society on December 6th., 11917 / by Frank Lee Pyman. Source: Wellcome Collection.

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    the same type of smell—for instance, the lower latty acids, whilst each member may have a specific odour—which, in this particular case, serves to distinguish the individual members from iormic to valeric acids. Sense of taste also provides an occasional means of discrimination, not only between side chains of different lengths —p-ethoxyphenylcarbamide (dulcine) being sweet, whilst the higher alkylphenylcarbamides are not—but also in certain cases between stereoisoinerides—^/-histidine, for example, tasting sweet, whilst Z-liistidine is tasteless. It is noteworthy that stereo¬ chemical influences often have profound effects on the physio¬ logical actions of quite different classes of compounds, particularly in actions on nerve-endings, as Cushny has pointed out (Lancet, September 9th, 1916, 459); thus, Z-hyoscyamine has about 100 times the mydriatic action of the rZ-variety and Z-adrenaline has many times the pressor effect of ^-adrenaline. In the case of pilocarpine, which contains two asymmetric carbon atoms, a change of sign of one of these results in the formation of the stereoisomeric Zsopilocarpine, which has only a fraction of the activity of pilo¬ carpine itself. The asymmetry of a nitrogen atom may also con¬ dition a difference in physiological action; when Z-canadine is methylated, a mixture of the a- and /3-methochlorides is obtained, the isomerism of which is due to the asymmetry of the nitrogen atom; these produce a typical curare effect (paralysis of nerve endings in voluntary muscle) in the frog, the /3-salt being, how¬ ever, twelve times as powerful as the a-salt. Stereoisomerides, however, do not always show large differences in physiological action, even in actions on nerve-endings; d- and Z-homatropine differ little from each other and r/Z-homatropine in mydriatic action, whilst rZ-cocaine, a stereoisomeride of natural laevorotatory cocaine, has a local anaesthetic action which, although quicker and more intense, is also more evanescent than that of cocaine. Very little is known about the cause of the variation in the physiological actions of stereoisomerides, but recently an explana¬ tion has been suggested by Windaus (Xac.hr. K. Ges. TP-iss. Gut tingen, 1916, 301) for the different physiological behaviour of the stereoisomerides /3- and e-cholestanol. These compounds differ greatly in their power of inhibiting the haemolytic action of saponins, such as digitonin, the former having this property in a high degree, whilst the latter has only slight preventive proper¬ ties. Now, the /8-compound has been found to combine with digitonin to give an almost inactive additive product, whilst e-cholestanol does not combine with digitonin. This case is of special importance, because of the close relation of the cholestanols to cholesterol, a constituent of the living