Agmatine: an endogenous clonidine-displacing substance in the brain

Beneficial circulatory effect of L-arginine

L-Arginine is an essential amino acid for infants and growing children. This amino acid is a substrate for at least five enzymes identified in mammals, including arginase, arginine-glycine transaminase, kyotorphine synthase, nitric oxide synthase (NOS) and arginine decarboxylase. L-Arginine exerts antihypertensive and antiproliferative effects on vascular smooth muscles. NOS and arginine decarboxylase appear to be important for the effect of L-arginine on the circulatory system, since each produces nitric oxide (NO), a potent vasodilator, and agmatine, an endogenous noncatecholamine ligand for central alpha-2 adrenoceptors, from L-arginine. Several issues must be clarified before the mechanisms by which L-arginine exerts its effects on the circulatory system can be fully understood.

Immunodetection of putative imidazoline receptor proteins in the human and rat brain and other tissues

A specific anti-imidazoline receptor (IR) protein antiserum was used to detect these putative receptors in brain and other tissues. In immunoblotting experiments, various brain areas and tissues expressed a double band of 29-30 kDa, and some of them bands of 47 and 66 kDa. The human medulla oblongata also showed bands of 44 and 50 kDa; and the rat adrenal medulla, bands of 58 and 86 kDa. Total immunoreactivity correlated with the density of IR binding sites in the various tissues. This is first evidence of heterogeneity of immunoreactive IRs in the mammalian brain.