How to "stop" an API call?

Question

JavaScript

Good afternoon.
I want to output variables to the template from the database. Made a service

import {Http} from 'angular2/http';
import {Injectable} from 'angular2/core';
import 'rxjs/Rx';

@Injectable()
export class MainService {
  public http:Http;
  public localhostUrl = 'http://localhost:3000/api/v1/main/text/';
  public pageTitleBase:Object = {};

constructor(http: Http) {
  this.http = http;
}
    getVar() {
     return this.http.get(this.localhostUrl)
          .map(res => res.json())
          .toPromise();
      }
}

and call it in the component

import {Component} from 'angular2/core';
import {CORE_DIRECTIVES} from 'angular2/common';
import {MainService} from '../../shared/services/main.service';
import {Title} from 'angular2/platform/browser';
@Component({
  selector: 'sd-home',
  moduleId: module.id,
  viewProviders: [MainService],
  templateUrl: './home.component.html',
  styleUrls: ['./home.component.css'],
  directives: [CORE_DIRECTIVES]
})
export class HomeComponent {
  public pageTitle : String;
  private text_content : Object;
  constructor (private _title:Title, private _main:MainService) {}
ngOnInit() { this.getTextContent(); }

    getTextContent() {
    
    this._main.getVar()
    .subscribe(text_content =>
    this.text_content = text_content,
    error =>  this.errorMessage = <any>error);

   }
}

And there is a constant call to the API, non-stop. How to make the data "climb" once and calm down on it?