Altrenogest

Details:

Progestins are primarily produced endogenously by the corpus luteum. They transform proliferative endometrium to secretory endometrium, enhance myometrium hypertrophy and inhibit spontaneous uterine contraction. Progestins have a dose-dependent inhibitory effect on the secretion of pituitary gonadotropins and also have some degree of estrogenic, anabolic and androgenic activity.
 
Altrenogest (or allyltrenbolone) is a synthetic trienic C21 steroidal progestomimetic, belonging to the 19-nor-testosterone series. It is an orally active (pro)gestagen. Like all steroids, altrenogest acts by its liposolubility by penetrating the target cells where it binds to specific receptors.
 
Altrenogest is indicated (labeled) to suppress estrus in mares to allow a more predictable occurrence of estrus following withdrawal of the drug. It is used clinically to assist mares to establish normal cycles during the transitional period from anestrus to the normal breeding season often in conjunction with an artificial photoperiod.
 
It is more effective in assisting in pregnancy attainment later in the transition period. One group of authors (Squires et al. 1983) suggest selecting mares with considerable follicular activity (mares with one or more follicles 20 mm or greater in size) for treatment during the transitional phase. Mares that have been in estrus for 10 days or more and have active ovaries are also considered to be excellent candidates for progestin treatment.

Altrenogest is effective in normally cycling mares for minimizing the necessity for estrus detection, for the synchronization of estrus and permitting scheduled breeding. Estrus will ensue 2-5 days after treatment is completed and most mares ovulate between 8-15 days after withdrawal. Altrenogest is also effective in suppressing estrus expression in show mares or mares to be raced.
 
Although the drug is labeled as contraindicated during pregnancy, it has been demonstrated to maintain pregnancy in oophorectomized mares and may be of benefit in mares who abort due to sub-therapeutic progestin levels.


 Applications:



Altrenogest is a steroid used for the control of estrus in horses. This drug can potentially be abused in racehorses as the occurrence of estrus can alter their performance. This work describes an analytical method based on liquid chromatography-tandem mass spectrometry for the detection of altrenogest in horse urine down to a concentration of 13 pg/mL. Furthermore, the qualitative aspect of metabolism of altrenogest in the horse has been studied.
 
The main transformations that were found for this species were conjugation with glucuronic acid and sulfate. These phase II metabolites were identified by molecular mass and by comparison of their collision-induced dissociation product ion spectra with that of the synthetic aglycone at positive and negative potential, respectively. No phase I metabolites were discovered. In order to increase the ionisation in positive electrospray, a derivatisation procedure forming a basic oxime was tested. This process significantly increased the detection sensitivity for altrenogest glucuronide in horse urine.

Adverse effects of altrenogest appear to be minimal when used at labeled dosages. One study (Shideler et al. 1983) found negligible changes in hematologic and most "standard" laboratory tests after administering altrenogest to 4 groups of horses (3 dosages, 1 control) over 86 days.
 
Occasionally, slight changes in Ca++, K+, alkaline phosphatase and AST were noted in the treatment group, but values were only slightly elevated and only noted sporadically. No pattern or definite changes could be attributed to altrenogest. No outward adverse effects were noted in the treatment group during the trial.
 

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