Systemic and regional hemodynamic effects of 1,25-dihydroxyvitamin D3 administration.
OBJECTIVE
To evaluate the cardiovascular effects of 1,25-dihydroxyvitamin D3 (1,25-D).


METHODS
Recent studies suggest that Ca-regulating hormones may contribute to the genesis of hypertension. We determined systemic and regional hemodynamics 24 h after administration of 1,25-D or vehicle to normal conscious Sprague-Dawley rats. In addition, to dissociate the vascular effects of 1,25-D from changes in serum ionized Ca2+, 1,25-D and vehicle were administered to rats maintained for 3 days on a low-Ca diet. To evaluate the effect of the slight rise in serum ionized Ca2+ with 1,25-D administration, we infused CaCl or vehicle over 1 h into normal rats to raise the serum Ca2+ to near that of rats treated with 1,25-D.


METHODS
The radioactive microsphere technique was used.


RESULTS
Systemic hemodynamics (blood pressure, heart rate, cardiac output, total peripheral resistance and stroke volume) did not differ between the two groups receiving a normal-Ca diet. In these rats 1,25-D significantly decreased renal blood flow (RBF), increased renal vascular resistance (RVR) and slightly increased serum ionized Ca2+. Similarly, in rats receiving a low-Ca diet, 1,25-D administration decreased renal blood flow, increased renal vascular resistance and caused only a minimal increase in serum ionized Ca2+. A low-Ca diet also increased heart rate, cardiac blood flow and renal blood flow. Although CaCl infusion raised serum ionized Ca2+, blood pressure, renal blood flow and renal vascular resistance did not change significantly.


CONCLUSIONS
1,25-D may constrict the renal vasculature directly or indirectly by enhancing the vascular sensitivity to circulating vasoconstrictors.
Roca-Cusachs
A
A
Department of Internal Medicine, University of Texas Medical Branch, Galveston 77550.
DiPette
D J
DJ
Carson
J
J
Graham
G A
GA
Holland
O B
OB
D000818:Animals; D002117:Calcitriol / Q000097:blood / Q000494:pharmacology*; D003326:Coronary Circulation / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D007583:Jejunum / Q000098:blood supply; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow / Q000187:drug effects; D012079:Renal Circulation / Q000187:drug effects; D013270:Stomach / Q000098:blood supply; D014655:Vascular Resistance / Q000187:drug effects
D002117:Calcitriol