ABSTRACT
The progestational, androgenic, myotrophic, and gonadotrophin-inhibiting activities of C21, C19, and C18 steroids have been correlated:
In the C21 steroid group, progestativomimetic action varies from 0.1 × progesterone (P) in the case of 17α-hydroxyprogesterone (HP) to 3 × P in the case of 17α-acetoxyprogesterone (AP); it is particularly high (15 × P) with 6α-methyl-17α-acetoxyprogesterone (MAP). These two acetoxyprogesterones are orally active, their activity being respectively 3 and 50 × that of 17α-ethinyltestosterone (ET). MAP is highly active in maintaining gestation, i. e. 42× P in the rat, and 25 × P in the rabbit. The androgenic effects of these steroids are confined to certain structures only. Only MAP displays marked myotrophic activity. Gonadotrophin-inhibiting activity which is low for P, increases for HP and AP and is greatest in the case of MAP, which in this respect is about 5 × more active than testosterone (T).
In the C19 steroid group, progestativomimetic action, which is weak with T (0.01 × P), is somewhat higher with 17α-methyltestosterone (MT) and even higher with ET (0.3 × P). This progression also holds good for oral activity as well as for maintenance of gestation. The low incidence of side effects with ET is worth noting.
Common to the C18 steroids is their very high oral progestativomimetic activity: 17α-methyl-19-nortestosterone (MNT) = 4 × ET; 17α-ethinyl-19-nortestosterone (ENT) = 3 × ET; 17α-methyl-△5–10-19-nortestosterone = 1.5 × ET; and 17α-allylestren-3-17β-ol (allylestrenol) = no less than 16 × ET. Their gestation-maintaining properties are weak with the exception of MNT (1 × P). All substances of this group, apart from allylestrenol, are more potent inhibitors of gonadotrophic function than testosterone.
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