Serum concentrations of 17beta-estradiol in ovariectomized rats during two times six weeks crossover treatment by daily injections in comparison with slow-release pellets.
Estrogens exert widespread biological functions that reach far beyond their well-known role in reproduction. Exogenous administration of 17beta-estradiol to ovariectomized experimental animals is of the utmost importance in elucidating its mechanisms of action. In the present study, we compared two different modes of exogenous administration of 17beta-estradiol to ovariectomized rats in relation to the serum 17beta-estradiol concentrations over prolonged periods of time. 17beta-estradiol was administered either by slow-release pellets (Innovative Research of America, Sarasota, Fl. 34236, USA, 90-day release, NHH-115, 1.5 mg) or by daily subcutaneous injections of 15 microg 17beta-estradiol dissolved in sesame oil. After 6 weeks, the mode of administration of estradiol was changed to the opposite method and continued for a further 6 weeks. Blood samples for measurement of serum 17beta-estradiol were taken every second week. After 2 weeks, the serum concentrations of 17beta-estradiol in group A initially receiving the pellets were 73 % higher (p<0.001) compared to those of group B receiving daily injections. The difference was even more prominent, 580 % (p<0.001), after 4 weeks. Steady state was reached at week 6 in group A, but already by week 4 in group B. Once steady state was reached, the concentrations were the same in both groups for the remainder of the experiment (12 weeks in total). Our study indicates that steady-state concentrations of 17beta-estradiol occur 5-6 weeks later than the 48 h the manufacturer of the slow-release pellets claims.
Theodorsson
A
A
Department of Clinical Chemistry, Linköping University Hospital, Linköping, Sweden. annette.theodorsson@telia.com
Hilke
S
S
Rugarn
O
O
Linghammar
D
D
Theodorsson
E
E
D000818:Animals; D004958:Estradiol / Q000008:administration & dosage* / Q000097:blood* / Q000493:pharmacokinetics; D005260:Female; D007267:Injections; D010052:Ovariectomy; D051381:Rats; D012715:Sesame Oil; D013997:Time Factors
D004958:Estradiol; D012715:Sesame Oil