Dear Laura

Dose is mainly concerned to obtain hyperglycemic animal. How could you analyze the dose by self feeding.

We trained common marmosets to drink a glucose solution from a syringe. Thus we could accurately measure the dose by weighing the syringe before and after. Marmosets find a glucose solution highly palatable. (paper is Power et al 2013 in Obesity)

I would be concerned about a sugar pellet, as the rate at which the sugar is absorbed might be more variable compared to a liquid dose.

If the animals drink the solution (as opposed to gavage) then there will be a cephalic phase effect due to the sweet taste. More realistic for normal physiology, but it depends on your question whether this is an advantage or a complication. 

For some questions I would see no problem with using a palatable solution the animals are familiar with that contains a consistent amount of glucose and other nutrients as long as you can accurately measure intake. Remember that there is an insulin response to amino acids as well as to glucose (in most species; I think this is true in rats). You are suggesting a mixed-nutrient meal; perfectly acceptable for many questions. possibly not if you are looking specifically at glucose metabolism.

It all depends on the questions you are asking and the purpose behind collecting your data.

Milk contains complex sugars, fats and aa as well. How will accurately measure the 75 gram glucose load in sweetened mik...I think it would make things more complicated.

In addition to some of the concerns pointed out by others, your zero time point, which is normally the time when concentrated glucose solution is given to a rat orally or through other routes, in a matter of just a few seconds, could greatly vary. This will complicate your results.

solid pellets of glucose will similarly entail similar problems.

oral gavage or ip injections are fairly simple and quick. If your concern in using them is lack of experience, try a few times on unrelated rats and you will quickly become familiar with the procedure.  

Best...

Thank you very much for your answers.

What I would like to know about my animal model is: Are baseline glucose levels elevated? And is the insulin response abnormal?

The model comes with several particularities compared to wild type rats: Reduced hunger, lower food intake, lower water intake, slower feeding speed of certain diets, lower lean mass, but higher fat mass.

As it is a model of neuronal dysfunction, the cephalic phase of insulin response might be particularly interesting, or better the comparison of pre- and postabsorptive responses.

The route of administration for investigating the postprandial phase would also be in question, as we don’t know anything about the rats’ gut function so far.

Thus, might it make sense to perform a larger study and investigate

1)  the response to a palatable diet the rats approach themselves (even though there might be increased variation),

2) the response after oral gavage feeding,

3) the response after intraveneous injection?

I guess, in case I would want to compare the three responses, I would need to use the same solution every time.

I wonder, does the stress of oral gavage feeding and injection as well as blood sampling not alter the hormonal response? Thus, would it need to be three separate cohorts of rats?

Any suggestions on the blood sampling method? Is a catheter required?

In general. it is always a good idea to get handle your animals for a few days prior to beginning the experiment. This allows the animals to become familiar with your touch and handling and helps them stay more calm. Yes, any addition stress will cause their blood glucose to go up, via catecholamine as well as cortisol. 

The level of stress experienced by the person who is conducting the experiment directly plays into the bigger picture and experience helps a great deal. If you are yourself not very experienced with animal handling or performing such procedures you need to conduct, try to find someone who is experienced and willing to help you in the beginning. This practice should include not only physically handling the animal but also doing a set of dummy runs. For example, practice oral gavage, iv or intravenous injections with saline and monitor blood glucose levels before and after. Once you have experience, the procedure will go very smoothly, take a few seconds and you will note minimal difference in glucose levels before and after the procedure.

Having relevant controls is a necessity.

If you are only measuring blood glucose levels, blood drawing is very simple through a small puncture on the tail vein using a fine needle (27G). The commonly used glucometers these days use no more than 1µl blood volume. On the other hand, if you are interested in measuring hormone levels as well, you have to weigh a few factors in your experimental design. If multiple hormone levels are to be assayed, you will need substantial volume of blood. This means that you have pick fewer time points that you can test. In case of glucose alone, one can do a group of 5 animals, where time points are 10min apart. Drawing blood takes longer time, consider doing 0, 20, 40, 60, 90, 120min at the most. You may have to drop to 0, 30, 60, 120 min depending on the size of the rats because collectively, in a day you can only draw a limited amount of blood.

Catheter in an anesthetized is convenient but it also entails the effect of anesthesia. Your decision will have to be guided by what questions are more critical for you to address.

Best...

This would neither be feasible nor advisable for the purpose.

Dear Lalit, what do you exactly refer to when you say not feasible or advisable?

Its a tuff thing. Milk is a complex thing and I can't think of any situation where adult experimental rats are likely to have access to lactose. In adult rats, I have observed that brush border lactase activity is negligible compared to sucrase. Milk treatment is likely to change that. With ad libitum feeding, insulin values are likely to be higher than usual. Under these conditions, it is tuff to measure glucose tolerance. Would it be possible to fast your rats overnight before ogtt? In that case u don't have to worry at all. Glucose soln in water will be great

Dear Laura

you may take into account the fact that in rodents oral glucose combined with some other easily digestible glucids and proteins (from milk) might induces a severe digestive dismicrobism. We VE HAD SUCH BAD EXPERIENCE IN CHINCHILAS, inducing secondary Clostridium infection