INFLUENCE OF LH-RF ON LH AND FSH RELEASES IN DOMESTIC MAMMALS
Jean Marc Pelletier · annales de biologie animale biochimie biophysique · 1976
Intravenous injection of LH-RF into intact rams induces LH release into the blood ; this is related to dose.No clear relationship, however, is observed for FSH.LH peak levels appear after a long time (about 2 hours after a ioo j i g synthetic LH-RF injection) ; the maximum level is about io ng/ml.Conversely, LH-RF injection given to castrated rams has a rapid effect ( 10 -20 mn), and the peak level is much higher then in intact rams ( 70 -8 0 ng/ml).This effect is observed as early as 3 hours post-castration.In castrated rams, acute testosterone propionate treatment, given 6 hours before LH-RF, decreases the intensity of LH release by 40 p. 100 , but does not modify the time needed to reach peak level.On the other hand, chronic testosterone propionate treatment delays the peak level but, in the conditions used, does not modify the magnitude of the LH peak.Thus, there is may be two different ways in which testosterone acts on LH release through LH-RF action : i) it decreases LH release after LH-RF ; 2 ) it delays LH peak time.In the male lamb, LH-RF injection induces LH patterns which vary with age.At 20 -6 0 days of age, LH response to LH-RF is immediate, as in castrates ; thereafter, there is progressive lengthening of this time, which reaches peak level in the intact adult at r 4 o days of age.Thus, a kind of maturity of the hypothalamohypophyseal system seems to be achieved only at puberty.In the ewe, intensity of LH release after LH-RF varies during the estrous cycle according to the plasma 1 73-oestradiolfprogesterone ratio, maximum LH release being observed at day 1 6 (ioo p. 100 ) and minimum release at day z2 (i 3 .5 p. ioo).During seasonal anestrus, LH release after LH-RF also varies according to physiological state : in dry ewes LH release is greater (about 40 p. roo) than in post partum lactating or non-lactating ewes.Influence of LH-RF on LH and FSH releases in other species is discussed in comparison with the above results.!....