Pharmacological characterization of KR-30988, a novel non-peptide AT1 receptor antagonist, in rat, rabbit and dog.

The pharmacological profile of KR-30988, a non-peptide AT1-selective angiotensin receptor antagonist, has been investigated by use of a variety of experimental models in-vitro and in-vivo. KR-30988 inhibited the specific binding of [125I][Sar1, Ile8]-angiotensin II to the recombinant AT1 receptor from man with a potency similar to that of losartan (IC50 values, the concentrations of drugs displacing 50% of specific binding, 13.6 and 12.3 nM, respectively), but did not inhibit the binding of [125I]CGP 42112A to recombinant AT2 receptor from man (IC50 >10 microM for both drugs). Scatchard analysis showed that KR-30988 interacted competitively with recombinant AT1 receptor from man in the same manner as losartan. In functional studies with rat and rabbit aorta, KR-30988 noncompetitively inhibited the contractile response to angiotensin II (pD2, = -log EC50 (where EC50 is the dose resulting in 50% of a reference contraction), 8.64 and 7.73, respectively) with a 20-85% decrease in the maximum contractile responses, unlike losartan. In pithed rats intravenous KR-30988 resulted in a non-parallel shift to the right of the dose-pressor response curve to angiotensin II (ID50 value, the dose inhibiting the pressor response to angiotensin II by 50%, 0.09 mg kg(-1)) with a dose-dependent reduction in the maximum responses; in this antagonistic effect KR-30988 was 20 times (approx.) more potent than losartan (ID50 1-74 mg kg(-1)). In conscious renal hypertensive rats oral administration of KR-30988 produced a dose-dependent and long-lasting (>24 h) anti-hypertensive effect; the potency was six times that of losartan (ED30 values, the dose reducing mean arterial blood pressure by 30 mmHg, 0.48 and 2.97 mg kg(-1), respectively). In conscious furosemide-treated dogs oral administration of KR-30988 produced a dose-dependent and long-lasting (>8 h) hypotensive effect with a rapid onset of action (time to Emax, the maximum effect, 1-2 h); KR-30988 was eight times more potent than losartan (ED20, the dose reducing mean arterial blood pressure by 20 mm Hg, 1.04 and 7.96 mg kg(-1), respectively). These results suggest that KR-30988 is a potent, orally active selective AT1 receptor antagonist with a mode of insurmountable antagonism.