[The effect of alpha adrenergic agents on lipolysis in rat adipose tissue; the effect of nonselective alpha adrenomimetics and alpha adrenolytics in an experiment in vitro].

It is now generally accepted, that in most of the animal species the adrenergic control of lipolysis from adipose tissue is mediated by adrenergic beta 1 and alpha 2 receptors. Therefore, the problem we deal with in this article is concerned with the role of alpha adrenergic receptors in lipolysis in the rat adipose tissue because only in this species the function of alpha adrenergic receptors in lipolysis is still not clear. In in vitro experiments with epididymal adipose tissue of adult rats (where we followed up the release of free fatty acids into the albumin medium) we found: 1) Alpha adrenergic blocking agents phentolamine and phenoxybenzamine had no influence on the lipid mobilizing effect of adrenergic agonists. This effect was absent also when drugs with the strong alpha sympathomimetic effects, e.g. norepinephrine and noroxedrine, were used. 2) On the other hand, alpha adrenergic agonist phenylephrine was able to antagonize in rat adipose tissue the lipid mobilizing effect of beta adrenergic agonist isoproterenol. 3) From our experiments it can be concluded, that phenylephrine acts as a competitive dualist on beta adrenergic receptors, it reduces the effect of full agonist (e.g. isoproterenol) to the level of its own maximum lipolytic effect. No participation of alpha adrenergic receptors in described effects of phenylephrine were detected, because neither the lipolytic, nor the lipolysis blocking effects of phenylephrine were influenced by alpha adrenergic blocking agents. Our studies using alpha adrenergic agonist phenylephrine or nonselective alpha adrenergic blocking agents did not indicate the presence of any alpha adrenergically controlled lipolysis in the rat adipose tissue. However, the role of antilipolytic alpha 2 adrenoceptors in rat adipose tissue cannot be completely excluded, some of these receptors were found on the membranes of rat adipocytes. Our future study deals with this problem.