It is in the ability descriptions, hp are explicitly changed when the modifier goes up or down.
Int is applied only at level up for skills and does not have the con statement about shifting skills known with int damage or enhancement bonuses or such.
Constitution (Con)
Constitution represents your character’s health and stamina. A Constitution bonus increases a character’s hit points, so the ability is important for all classes.
You apply your character’s Constitution modifier to:
Each roll of a Hit Die (though a penalty can never drop a result below 1—that is, a character always gains at least 1 hit point each time he or she advances in level).
Fortitude saving throws, for resisting poison and similar threats.
Concentration checks. Concentration is a skill, important to spellcasters, that has Constitution as its key ability.
If a character’s Constitution score changes enough to alter his or her Constitution modifier, the character’s hit points also increase or decrease accordingly.
Intelligence (Int)
Intelligence determines how well your character learns and reasons. This ability is important for wizards because it affects how many spells they can cast, how hard their spells are to resist, and how powerful their spells can be. It’s also important for any character who wants to have a wide assortment of skills.
You apply your character’s Intelligence modifier to:
The number of languages your character knows at the start of the game.
The number of skill points gained each level. (But your character always gets at least 1 skill point per level.)