Ovariectomy and 17β-estradiol Replacement in Rats and Mice: A Visual Demonstration

Summary

Ovariectomy and subsequent replacement of 17β-estradiol by means of silastic capsules and peroral Nutella are demonstrated in rats and mice.

Abstract

Estrogens are a family of female sexual hormones with an exceptionally wide spectrum of effects. When rats and mice are used in estrogen research they are commonly ovariectomized in order to ablate the rapidly cycling hormone production, replacing the 17β-estradiol exogenously. There is, however, lack of consensus regarding how the hormone should be administered to obtain physiological serum concentrations. This is crucial since the 17β-estradiol level/administration method profoundly influences the experimental results^1-3. We have in a series of studies characterized the different modes of 17β-estradiol administration, finding that subcutaneous silastic capsules and per-oral nut-cream Nutella are superior to commercially available slow-release pellets (produced by the company Innovative Research of America) and daily injections in terms of producing physiological serum concentrations of 17β-estradiol^4-6. Amongst the advantages of the nut-cream method, that previously has been used for buprenorphine administration⁷, is that when used for estrogen administration it resembles peroral hormone replacement therapy and is non-invasive. The subcutaneous silastic capsules are convenient and produce the most stable serum concentrations. This video article contains step-by-step demonstrations of ovariectomy and 17β-estradiol hormone replacement by silastic capsules and peroral Nutella in rats and mice, followed by a discussion of important aspects of the administration procedures.

Protocol

1. Ovariectomy via the Dorsal Route

1. Anesthetize the animal, for example using 1.5% isoflurane (4% for induction) in an oxygen/nitrous oxide 30%/70% mixture. Place the animal in prone position on a heating plate connected to a rectal thermometer. It is important to have a thin layer of isolation between the animal and the plate, and that the thermometer feed-back system keeps the body temperature within 37 ± 0.5 °C. Apply gel for eye protection and administer 5 mg Rimadyl/kg bodyweight diluted in saline subcutaneously on the lateral aspect of the animal's neck for postoperative pain relief.
2. Shave a 4*4 cm (3*3 cm for mice) area cephally from the i....

Discussion

The administration modes presented above have in earlier studies proved superior to commercial slow-release pellets and injections in terms of producing physiological serum concentrations of 17β-estradiol. While the slow-release pellets produce very high and prolonged serum concentration peaks, the injections cause extreme, daily hormone fluctuations and require repeated stressful handling of the animals ^4-6. The importance of choosing adequate administration modes is highlighted by recent studies indicat.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Rimadyl, 50 mg/mL	Pfizer Pharma GmbH	462986	Postoperative analgesia after ovariectomy.
Lubrithal eye gel	Leo Laboratories		Eye protection during surgery.
Jodopax vet	Pharmaxim		Surgery disinfection.
Vicryl 4-0 suture	Johnson & Johnson		Wound suture and ovary ligation.
17β-estradiol, >98%	Sigma-Aldrich	E8875-1G	In sesame oil for silastic capsules and Nutella.
Sesame oil	Sigma-Aldrich	S3547-1L	Dissolving the 17β-estradiol.
Silastic tubing, ID/OD: 1.575/3.175 mm	Dow Corning	508-008	Production of silastic capsules.
Wooden applicator stick	Selefatrade	12-0783	Capping of silastic capsules.
Nutella	Ferrero		Medium for peroral 17β-estradiol.