Vol. 282, Issue 4, R952-R959, April 2002
Enhanced vascular effects of the Ca2+ channel
agonist Bay K 8644 in pregnant rabbits
Rocco
Venuto1,
Gail
Brown2,
Marion
Schoenl1, and
György
Losonczy1,3
1 Schools of Medicine and Biomedical Science and
2 Nursing, University at Buffalo, State University
of New York, Buffalo, New York 14215; and 3 Department
of Pulmonology, Semmelweis University Medical School, Budapest 114, 1536 Hungary
Hemodynamic studies were
performed to determine if blunting of vascular pressor responsiveness
to vasoconstrictors during pregnancy may be due to impaired L-type
voltage-dependent calcium channels (L-VDCC). Bay K 8644 (BAY), an
L-VDCC agonist, was infused in pregnant and nonpregnant anesthetized
rabbits (10, 20, 40, and 60 µg/kg) and pregnant and nonpregnant
conscious, chronically instrumented (conscious) rabbits (10, 25, and 50 µg/kg). BAY infusions resulted in greater elevation of mean
arterial pressure in both anesthetized pregnant (n = 6)
vs. nonpregnant (n = 6) (P < 0.05) and
conscious pregnant (n = 10) vs. nonpregnant
(n = 10) rabbits (P < 0.05).
Fractional increase over baseline of total peripheral resistance index
was greater in pregnant (36 ± 5 to 78 ± 14%) vs.
nonpregnant rabbits (14 ± 4 to 52 ± 6%) (P < 0.02). Cardiac output index did not differ. There was a single
high-affinity L-VDCC antagonist aortic binding site with similar number
and affinity in pregnant (n = 7) and nonpregnant
(n = 7) rabbits. In conclusion, stimulation of L-VDCC
induces greater pressor responses in pregnant rabbits with heightened
peripheral vasoconstriction. This does not appear to be due to a change
in L-VDCC receptor parameters.
blood pressure; vascular reactivity; calcium channels; nifedipine
