For the 3750, it's off.
For the 4500, depends:
The default settings for Gigabit Ethernet interfaces are as follows:
•Sending pause frames is off-non-oversubscribed Gigabit Ethernet interfaces.
•Receiving pause frames is desired-non-oversubscribed Gigabit Ethernet interfaces.
•Sending pause frames is on-Oversubscribed Gigabit Ethernet interfaces.
•Receiving pause frames is desired-Oversubscribed Gigabit Ethernet interfaces
The default settings for Tengigabit Ethernet interfaces are as follows:
•Sending pause frames is off.
•Receiving pause frames is on.
It's really platform specific.
