If your product is orally active (quite a lot of hormone preparations are not!) you have several choices . If not, some way of direct administration is required. Thus much depends on the properties of the product you want to test. Also is it water soluble or not and is it stable in water?

Your animals will probably adapt rather quick to daily handling, but it will almost certainly cause some stress, which might interfere with your observations.

Does it need to be oral? If you are suggesting minipumps perhaps not. In the case it can be intraperitoneal, I would look into implanting an intraperitoneal catheter. I am not sure if these come with the same high maintenence and patency issues as intravenous catheters or would last for six months, but this would be an easy way of giving low-stress injections. Also, I agree with the previous answer; if using good technique, the rats will become accustomed to daily handling and i.p. injections. Even if this is not perfectly ideal, plenty of behavioral studies have used daily i.p. injections over long periods of time (months).

If it needs to be oral, and I am not sure about the other concerns of your study, you could also dissolve your hormone in a water solution and give it to rats which are water-deprived. If it is mostly flavorless (or not bitter), the rats should drink several mL rapidly upon access to the bottle. Just allow them access to the experimental solution until they finish their dose and then allow them several more minutes access to plain water every day; then take away water access until the next day when you give the experimental solution again. Alternatively, you could put your hormone in a sucrose solution (maybe 10% sucrose in water) and give the rats a fixed amount (a few mL) to drink daily. This would likely require less water restriction since rats love sweet solutions. Certainly these would be the lowest-stress on the rats and easiest ways for you. They may sacrifice a bit of precision in your dosing, but with some careful considerations you should be able to get it working. Let me know if you want to discuss some more.

Hi Jesse,

There are certainly implants that last longer than osmotic pumps:

Article Controlled Delivery of a GnRH Agonist by a Silastic Implant ...

It depends on what your specific endocrine goals are.

It looks like these pellets go to 3 months:

http://www.belmatech.com/en/

Your best bet may be to contact innovate research for a custom pellet:

http://www.innovrsrch.com/faq.asp

I've used osmotic pumps and pellets from innovative research. Both work great.

Probably you will need approval from an Animal Ethics Committee. Consult them to be sure that whatever you choose has a fair chance of being approved.

Add your drug to sweetened condensed milk and administer daily via syringe

If you hormone has oral bioavailability and is light stable you can also administer it in food or drinking water. Blood and brain levels when we have done this are comparable to injections as far as absolute amount and variability. There are several vendors that will make "medicated" chow if you hormone is not water soluble.

I have experience with iPrecio programmable minipumps. They work for quite long periods, and the drug reservoir can be refilled through the skin with a syringe.

Hi Jesse,

if you know that the hormone you'll deliver can survive the digestive tract, we used cookies containing our drug of interest (in our case sertraline or fluoxetine, but works as well with different molecules, including endocrine disrupters). The rats love it! DOI: 10.1155/2014/123026 . However, one of the problem you might have with your hormone is the stability once it reaches the plasma. The liver will probably rapidly metabolize your hormone, so you'll end up with a peak of hormone concentration right after administration, then a rapid decline. However, it might be what you want if you want to model human oral uptake of medication. Please feel free to contact me if you need further information on the "protocol" Good luck

Hi Jesse,

Similar to Thierry's point above. We have used apples as an effective agent to administer hormones (i.e. melatonin) over the long term. See this paper for methods:

Article MT1 Melatonin Receptors Mediate Somatic, Behavioral, and Rep...

Thanks everyone for your well thought out responses, they have all been extremely helpful.

You can by a micro syringe.

Regards

Hi Jesse,

I am from the manufacturer of iPRECIO pumps. I am very late but I thought I would still share. Our pumps will infuse up to 6 months at 1ul/hour. See www.iprecio.com for the latest. You can even program the pump to infuse intermittently or to try to simulate the hormonal cycle. Please note that our pumps are not compatible with oil which is frequently used used to dissolve/deliver hormones. Propolyne glycol (PG) is compatible and may be worth the cost if you would like to try to simulate the hormonal cycle and get up to 6 months infusion with minimal handling.

Some references for the choices you mentioned.

Article Administration of Substances to Laboratory Animals: Routes o...

https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/routes-of-administration

Good luck and feel free to contact if you have more questions.