Abstract
Albino rabbits were administered either vasodilative agents (acetylcholine, benzyl imidazoline hydrochloride and Kallikrein) or vasoconstrictive agents (adrenalin and ephedrine), each alone or in combination with thiamine. The concentrations of thiamine in the blood, retina, optic nerve and choroid were estimated. In the case of an administration of vasodilative agents alone, the thiamine concentrations increased as soon as 5 minutes after the injection in some cases, reaching their peaks in 15 to 30 minutes, and began to return to normal in 60 minutes in almost all cases. A marked increase of thiamine in the optic nerve only was resulted by the administration of each vasodilative agent with thiamine. When acetylcholine was given combined with thiamine, the concentration of thiamine in the blood increased. Phosphorylation was, however, accelerated in almost all cases. The thiamine concentration in ocular tissues began to decrease in 5 minutes after adrenalin administration, reaching its minimum in 15 to 30 minutes and turned to return to normal thereafter. The administration of ephedrine resulted in a marked transition of thiamine into the ocular tissues. But after two hours, it returned to the normal value. A simultaneous application of adrenalin with thiamine resulted in an inhibition of thiamine transition from the blood to the ocular tissues. This inhibition was not observed by the application of ephedrine with thiamine. The administration of vasodilative agents results in a dilatation of the blood vessels and an increase in the amount of circulating blood in the eyeball, leading to an increased permeability in the blood retinal barrier. Furthermore it may result in an accerelated glycolysis and phosphorylation of thiamine followed by an increased production of energy in the ocular tissues. When adrenalin is given, the effect on the other endocrine glands and stress syndrome should be considered in addition to its vasoconstrictive effect. Ephedrine does not inhibit the thiamine-transfer from the blood to the retina and optic nerve, because its vasoconstrictive effect is slighter with short duration.
