title: Effect of gamma-L-glutamyl-L-dopa on phosphate excretion.
abstract: gamma-L-glutamyl-L-DOPA (gludopa) is a dopamine prodrug that is relatively specific for the kidney. Because dopamine is phosphaturic, the present study compared the phosphaturic effects of the infusion of equimolar doses of gludopa (n = 8), L-DOPA (n = 8), and gamma-L-glutamyl-L-tyrosine (glutyrosine, n = 6). Glutyrosine was used as a control to evaluate the effect of the glutamyl portion of gludopa on phosphate excretion. Sprague-Dawley rats (350 to 400 g) were anesthetized with 5-sec-butylethyl-2-thyobarbituric acid (Inactin; 100 mg/kg, IP) and underwent thyroparathyroidectomy. Clearances were taken during the infusion of normal saline vehicle, followed by the infusion of gludopa, L-DOPA, or glutyrosine, all infused at the rate of 10 nmol/kg bolus and 0.8 nmol/kg/min (iv). To determine the contribution of glutamyl derivative to phosphate excretion, gludopa or L-DOPA was infused in the presence of SCH23390, a DA-1 receptor antagonist. Gludopa infusion significantly increased dopamine excretion (from 1.9+/-0.2 ng/min to 17.0+/-3.9 ng/min, delta15.0+/-3.9 ng/min, P < .008) and fractional excretion of phosphate (from 2.6%+/-0.6% to 34.8%+/-1.8%, delta32.0%+/-1.6%, P < .001). L-DOPA infusion significantly increased dopamine excretion (from 1.4+/- 0.4 ng/min to 9.7+/-1.6 ng/min, delta8.3+/-1.5 ng/min, P < .001) and fractional excretion of phosphate (from 1.7%+/-0.6% to 8.2%+/-2.0%, delta6.4%+/-1.5%, P < .004). Glutyrosine infusion significantly increased fractional excretion of phosphate (from 2.8%+/-0.8% to 17.5%+/-5.2%, delta14.6%+/-4.8%, P < .03) without changing dopamine excretion (delta0.5+/-0.2 ng/min). Infusion of gludopa in the presence of SCH23390 increased fractional excretion of phosphate (from 5.7%+/-2.5% to 12.6%+/-3.5%, delta6.8%+/-2.3%, n = 6, P < .03), whereas SCH23390 completely blocked the phosphaturic effect of L-DOPA. We conclude that gamma-L-glutamyl-L-DOPA is more phosphaturic than L-DOPA in the rat because of the combined effects of dopamine and the glutamyl moiety.
authors.affiliation: Department of Medicine, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA.
authors.forename: S
authors.initials: S
authors.lastname: Sadiq
authors.forename: T J
authors.initials: TJ
authors.lastname: Berndt
authors.forename: K A
authors.initials: KA
authors.lastname: Nath
authors.forename: F G
authors.initials: FG
authors.lastname: Knox
mesh_terms: D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D004295:Dihydroxyphenylalanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004151:Dipeptides / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D005919:Glomerular Filtration Rate / Q000187:drug effects; D007275:Injections, Intravenous; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism; D007980:Levodopa / Q000037:antagonists & inhibitors / Q000494:pharmacology; D008297:Male; D010710:Phosphates / Q000652:urine*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D001552:Benzazepines; D004151:Dipeptides; D018492:Dopamine Antagonists; D010710:Phosphates; D007980:Levodopa; C017342:gamma-glutamyl DOPA; D004295:Dihydroxyphenylalanine; C054674:gamma-glutamyltyrosine