ABSTRACT
The questions raised are: what is the physiological or pharmacological basis for the differentiation into beta 1- and beta 2-, and alpha 1- and alpha 2-adrenergic receptors?; and do the neurotransmitter norepinephrine and the hormone epinephrine differ in their receptors? On the basis of a preference of beta 2- and alpha 2-adrenergic receptors for epinephrine, the hormone, and of beta 1-and alpha 1-receptors for norepinephrine, the neurotransmitter, it was postulated that the alpha 2- and beta 2-receptors are predominantly epinephrinergic in nature and located extrajunctionally and presynaptically whereas the alpha 1- and beta 1-receptors are predominantly norepinephrinergic in nature and located postsynaptically in the sympathetic terminal junction. The alpha 2- and beta 2-character of the presynaptic receptors matches that of the corresponding extrajunctional receptors. This indicates that a circulating catecholamine, namely epinephrine, is involved in the regulation of adrenergic transmitter release.
Subject(s)
Receptors, Adrenergic , Adrenergic alpha-Antagonists/pharmacology , Adrenergic beta-Antagonists/pharmacology , Amphibians , Animals , Cats , Cattle , Classification , Epinephrine/physiology , Guinea Pigs , Heart/drug effects , Humans , Mice , Neurotransmitter Agents/physiology , Norepinephrine/physiology , Rabbits , Rats , Receptors, Adrenergic/pharmacology , Receptors, Adrenergic/physiology , Receptors, Adrenergic, alpha/physiology , Receptors, Adrenergic, beta/drug effects , Receptors, Adrenergic, beta/physiology , Synapses/physiologyABSTRACT
The toxic potential of formaldehyde has recently been widely discussed, including the consequences of its release from certain building materials. The action of methenamine, used in the treatment of urinary infections, is based on the release of formaldehyde in the body. Various aspects of formaldehyde toxicity are discussed as a basis for reevaluation of methenamine and reconsideration of its safety.
