Well, what could reasonably be meant? An injection that would dissolve a female cat’s ovaries while leaving her otherwise healthy? Yeah, right. Or conversely, one that would fry the testicles with no other damage?
Well, an FDA approved injectable sterilization product is already on the market for male dogs that works by eliminating testosterone required for sperm production. And there is millions more in reward money out there for the successful development of other chemical castration techniques. Neutering by needle is definitely going to happen in our lifetimes. :)