Abstract
OBJECTIVE: To study the effects of a high-calcium diet upon blood pressure, vascular smooth muscle contractions and intracellular free calcium in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats.
DESIGN: Eight-week old animals were placed on a normal-calcium diet (1.1% calcium; SHR and WKY rat groups) or a high-calcium diet (2.1% calcium; Ca-SHR and Ca-WKY rat groups) and observed for 12 weeks.
METHODS: Blood pressure was measured indirectly by the tail-cuff method and in vitro smooth muscle responses were studied using a standard organ bath chamber. Platelets were used as a cell model for analysis of intracellular free calcium concentration, measured by the fluorescent indicator Quin-2.
RESULTS: The blood pressure of Ca-WKY and WKY rats did not differ, but increased systolic blood pressure was attenuated in Ca-SHR compared with SHR. The concentration-response curves of mesenteric arterial rings for potassium chloride and noradrenaline were not affected by the high-calcium diet in either SHR or WKY rats. The time required for total relaxation after washout of contractile agents (washout time) was shortest in WKY and Ca-WKY rats after both agonists, and shorter in Ca-SHR than in SHR after noradrenaline. Smooth muscle responses were also studied by contracting the preparations with noradrenaline and potassium chloride in a calcium-free solution, after which, calcium was added to the organ bath in increasing concentrations. Calcium contraction responses were similar in WKY and Ca-WKY rats; SHR displayed an attenuated response to calcium addition in mesenteric rings stimulated by both agonists. After potassium chloride as agonist, the responses of SHR and Ca-SHR did not deviate but, after noradrenaline, a significant shift in the calcium contraction curve towards the normotensive curve was observed in Ca-SHR. Intracellular free calcium was clearly lower in WKY rats than in SHR, and was significantly reduced by calcium supplementation in the hypertensive but not the normotensive animals.
CONCLUSIONS: A reduction in intracellular free calcium concentration and an effect upon receptor-mediated vascular smooth muscle contraction and excitation-contraction coupling may participate in the blood pressure lowering effect of a high-calcium diet.
| Original language | English |
|---|---|
| Pages (from-to) | 255-63 |
| Number of pages | 9 |
| Journal | J Hypertens |
| Volume | 10 |
| Issue number | 3 |
| Publication status | Published - Mar 1992 |
| Externally published | Yes |
| Publication type | A1 Journal article-refereed |
Keywords
- Analysis of Variance
- Animals
- Blood Platelets/chemistry
- Blood Pressure/drug effects
- Calcium/blood
- Calcium, Dietary/administration & dosage
- Dose-Response Relationship, Drug
- Hypertension/blood
- Male
- Muscle Contraction/drug effects
- Muscle, Smooth, Vascular/drug effects
- Norepinephrine/pharmacology
- Potassium Chloride/pharmacology
- Rats
- Rats, Inbred SHR/physiology
- Rats, Inbred WKY