How many variables should a constructor have?

I realize this is a pretty open question and could get a variety of answers, but here goes.

Using C# (or Java, or any OO language), is there a general rule that states how many variables should be passed into the constructor? The number of variables I am passing into the constructor of the extended classes seem to be getting out of hand.

In an effort to encapsulate the data of a class, I declare the members private, initialize them in my constructor, and use public accessors.

Here is an example:

public class A
{
  private int var1;
  private int var2;
  private int var3;

  //3 variables passed in
  public A(int v1, int v2, int v3)
  {
    var1 = v1;
    var2 = v2;
    var3 = v3;
  }

  //Properties (accessors) here
}

public class B : A
{
  private int var4;
  private int var5;

  //5 variables passed in
  public B(int v1, int v2, int v3, int v4, int v5)
  : base(v1,v2,v3)
  {
    var4 = v4;
    var5 = v5;
  }

  //Properties (accessors) here
}

public class C : B
{
  private int var6;
  private int var7;

  //7 variables passed in !!!
  public C(int v1, int v2, int v3, int v4, int v5, int v6, int v7)
  : base(v1,v2,v3,v4,v5)
  {
    var6 = v6;
    var7 = v7;
  }

  //Properties (accessors) here
}

My constructors are usually passing in different objects, not just ints. I started questioning my design when I started passing in 7 variables to the constructor of the child class, but I have also had trouble figuring out a different way to do this.

Is this considered bad programming practice? Is there a general limit to the number of variables you should pass into a constructor?