The short answer is no; if you're extracting the oxygen from the blood of an octopus of any size or age, then you don't have to worry about hormones coming along for the ride. How can I be so sure of that? Well, we've been extracting medical grade pure oxygen from the atmosphere for some time for use in a range of applications including the treatment of most diving-related injuries and by comparison to the complex organic compounds that hormones are, nitrogen and CO2 would appear to be harder to separate from the oxygen.
Now, as I understand it, most gas separation is done through low temperature separation techniques that involve getting gases down to a temp where one of the gases condenses but the other doesn't, and then just collecting the remaining gas or liquid depending on which you're interested in. It's possible that some organic compounds would have a similar melting or boiling point as oxygen, but I believe that's very unlikely because it's so low a temperature (around 90o Kelvin). Organic compounds, especially hormones are far more likely to liquid or solid at normal body temps of above 300o Kelvin.
But, I have to ask as a frame challenge; why on earth would you be extracting the oxygen from an octopus' blood in the first place? It would have to be the most inefficient method one can conceive of for gathering oxygen for a medical treatment for humans. We can and do already get it straight out of the air, and even if that wasn't possible for some reason there has to be some other source than octopedes which extract it from oxygenated water themselves. This means that the octopus relies on phytoplankton to create the oxygen in the water, then have to extract it for their own use, which we then extract for ours? That would require a small farm of octopedes1 to supply a single patient when we could extract the oxygen from the atmosphere directly and already do.
If there is a significant plot reason for doing this then so be it, but be aware you're going to have to explain this contrivance pretty clearly to suspend the disbelief of the majority of the population.
Edit: Based on further comments, it's possible that some form of biological symbiosis could exist between a man and an octopus, but if it's for oxygen exchange, it's more likely to benefit the octopus than it is the man for the reasons stated above. A human is far more likely to be able to support an octopus' oxygen needs than the other way around. That said, if there is some form of biological interface, it is also far more likely that a hormone exchange is possible. The likelihood of transfer of biological material would depend entirely on the nature of the biological interface supporting the symbiosis.
1. According to this paper
, an octopus of approx. 2.3Kg will use around 3.2 Litres of oxygen every day. A human consumes around 550 Litres of oxygen each day, meaning that you would need around 172 octopedes to cover off your own oxygen requirements and leaving nothing for the octopus. Increasing the size of the octopus doesn't help much because the weight-specific oxygen consumption of octopedes is (fractionally) inversely proportional to their size. Also, octopedes, while high consumers of oxygen by comparison to related species, tend to operate at much lower oxygen saturation levels (as little as 11%) to humans.