L-prolyl-L-leucyl-glycinamide analogues--a new class of peptide antihypertensives.

Accumulating evidence suggests that there is an increase in the density (maximum binding sites) of striatal dopamine receptors in the central nervous system of spontaneously hypertensive rats (SHR). A tripeptide of hypothalamic origin, PLG (L-Prolyl-L-Leucyl-Glycinamide) has been found to have modulatory effect on the dopamine receptors in the central nervous system of rats. Two analogues of PLG with cyclic amino-acid residues, L-Prolyl-L-Leucyl-(-)-thiazolidine-2-carboxamide and L-Prolyl-L-Leucyl-(+)-thiazolidine-2-carboxamide, have shown antihypertensive effect at the established phase of hypertension in 16-week old SHRs at a dose of 35 mg/kg per day per 7 days i.p. It was also observed from studies of radioligand [3H]-spiroperidol binding that the laevo-isomer of the PLG analogue has down-regulated the up-regulated dopamine receptors. Our findings confirm the role of central dopaminergic pathways in the pathogenesis of hypertension in SHR.