Voluntary Oral Administration of Losartan in Rats

Gavage is a widely performed technique for daily dosing in laboratory rodents. Although effective, gavage comprises a sequence of potentially stressful procedures for laboratory animals that may introduce bias into experimental results, especially when the drugs to be tested interfere with stress-dependent parameters. We aimed to test vehicles suitable for drug delivery by voluntary ingestion in rats. Specifically, Male Wistar rats (age, 2 to 3 mo) were used to test nut paste (NUT), peanut butter (PB), and sugar paste (SUG) as vehicles for long-term voluntary oral administration of losartan, an angiotensin II receptor blocker. Vehicles were administered for 28 d without drug to assess effects on the glucose level and serum lipid profile. Losartan was mixed with vehicles and either offered to the rats or administered by gavage (14 d) for subsequent quantification of losartan plasma levels by HPLC. After a 2-d acclimation period, all rats voluntarily ate the vehicles, either alone or mixed with losartan. NUT administration reduced blood glucose levels. The SUG group had higher concentrations of losartan than did the gavage group, without changes in lipid and glucose profiles. Our results showed that NUT, PB, and SUG all are viable for daily single-dose voluntary ingestion of losartan and that SUG was the best alternative overall. Drug bioavailability was not reduced after voluntary ingestion, suggesting that this method is highly effective for chronic oral administration of losartan to laboratory rodents.Oral administration, whether by gavage or voluntary ingestion, is a common method for providing a single daily dose of drug to animal models. Gavage is widely performed for precise oral dosing in rodents, particularly in efficacy, toxicity, and drug discovery studies. This technique, applicable in unanesthetized animals, is a rapid and efficient mean of accurately delivering fixed doses of the drug to be tested.³⁰ However, gavage comprises a sequence of procedures that are potentially stressful for laboratory animals. The removal of an animal from its cage, its manual restraint, and the insertion of a flexible or rigid dosing cannula into the esophagus with direction to the stomach all cause high levels of stress, even in trained animals.^2,5 In addition, the use of gavage is associated with welfare issues when it is done by inexperienced people or in long-term studies.¹³ Indeed, gastroesophageal aspiration and pulmonary injury represent recurrent complications of gavage dosing of rodents that can be triggered by technical errors.⁸ Moreover, the use of gavage for various drugs and vehicles can elicit a significant stress response in a vehicle- and dose-volume–dependent fashion.⁵When testing antihypertensive drugs, a noninvasive and stress-free method for drug delivery is crucial, because any source of external stress on rodents can significantly increase heart rate and blood pressure^3-5,18 and therefore potentially confound the experimental results.Several alternatives to gavage, which require less human involvement, have been tested in recent years. The administration of a drug mixed with an attractive vehicle by voluntary ingestion seems to be an effective, noninvasive method.^12,15 In previous attempts to refine the gavage procedure, nut paste has been successfully used for analgesic drug delivery^1,12,15,17 and is a promising option for estrogen administration.¹⁴ Other alternatives involve the use of pill dosing method,³² flavored gelatin (‘jello’) preparations,¹⁰ sugar cookie dough,⁷ honey,¹⁹ and syringe-feeding.²In our study, we used nut paste (NUT), peanut butter (PB), and sugar paste (SUG) as drug vehicles due to their palatability, consistency, and previously reported results. We aimed to investigate the suitability of these vehicles for voluntary oral administration and, as an alternative method to gavage, for the chronic administration of losartan to laboratory rats. We hypothesized that low amounts of these vehicles, even when administered to rats over a long period of time, would not induce relevant changes in blood glucose or lipid profiles and would efficiently deliver the tested drug, as assessed by losartan serum concentrations. Accordingly, we further hypothesized that the serum concentrations of the drug delivered by voluntary ingestion would be at least as high as that obtained by using gavage.