The pharmacokinetics of 125I-atrial natriuretic factor in anaesthetized rats. Effects of neutral endopeptidase inhibition with candoxatrilat and of ANF-C receptor blockade.
The effects of candoxatrilat (cis-4-([2-carboxy-3-(2-methoxyethoxy)propyl]-1-cyclopentanecarbonyla mino)- 1-cyclohexane carboxylic acid) and the ring-deleted atrial natriuretic factor (ANF) analogue C-ANF4-23 (des[Gln18, Ser19, Gly20, Leu21, Gly22]ANF4-23-NH2) on the clearance of (3-[125I]iodotyrosyl28)ANF (125I-ANF) were studied in both intact and nephrectomized anaesthetized rats. HPLC analysis was used to verify that the 125I-labelled material isolated by solid phase extraction of rat plasma was intact ANF. In intact animals, clearance of 125I-ANF was biphasic with a T1/2 alpha of 17 sec and T1/2 beta of 95 sec. Volume of distribution (Vd) was 564 mL/kg and plasma clearance (Clp) 248 mL/min/kg. Candoxatrilat, over the dose range 0.01-10 mg/kg i.v., increased T1/2 beta (by a maximum of 56%) and decreased Clp (by up to 52%) with no effect on T1/2 alpha or Vd. C-ANF4-23 (10 micrograms/kg+1 microgram/kg/min i.v.) reduced Vd (by 57%) and Clp (by 54%) with no effect on T1/2 beta, whilst abolishing the T1/2 alpha phase in over 50% of animals. Increasing the dose of C-ANF4-23 did not increase the effect on any of these parameters, apart from a small increase in T1/2 beta. Combining the two agents resulted in a substantial decrease in Clp (76%) whilst the reduction in Vd and increase in T1/2 beta were comparable to those seen with C-ANF4-23 and candoxatrilat alone, respectively. In nephrectomized rats, the pharmacokinetics of 125I-ANF and the changes induced by candoxatrilat were similar to those observed in intact animals, whilst the effects of C-ANF4-23 alone were greater than in intact animals. The combination of C-ANF4-23 and candoxatrilat again produced a substantial increase in T1/2 beta (153%) and decreases in Vd (55%) and Clp (78%) in nephrectomized animals, although these changes could not be distinguished from those seen in intact animals treated with the same combination. Our studies indicate that neutral endopeptidase and ANF-C receptors are both major, and approximately equal, clearance mechanisms for 125I-ANF, together accounting for at least 75% of the total clearance of this peptide in the rat.
Barclay
P L
PL
Department of Cardiovascular Biology, Pfizer Central Research, Sandwich, Kent, U.K.
Bennett
J A
JA
Greengrass
P M
PM
Griffin
A
A
Samuels
G M
GM
Shepperson
N B
NB
D000595:Amino Acid Sequence; D000818:Animals; D009320:Atrial Natriuretic Factor / Q000097:blood / Q000302:isolation & purification / Q000493:pharmacokinetics* / Q000494:pharmacology*; D002851:Chromatography, High Pressure Liquid; D003509:Cyclohexanecarboxylic Acids / Q000494:pharmacology*; D006207:Half-Life; D007457:Iodine Radioisotopes; D008297:Male; D008657:Metabolic Clearance Rate; D008969:Molecular Sequence Data; D009392:Nephrectomy; D015260:Neprilysin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010446:Peptide Fragments / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017461:Receptors, Atrial Natriuretic Factor / Q000187:drug effects*
D003509:Cyclohexanecarboxylic Acids; D007457:Iodine Radioisotopes; D010446:Peptide Fragments; C065367:atrial natriuretic factor (4-23)NH2, de-Gln(18)-de-Ser(19)-de-Gly(20,22)-de-Leu(21)-; C060942:candoxatrilat; D009320:Atrial Natriuretic Factor; D015260:Neprilysin; D017461:Receptors, Atrial Natriuretic Factor