Photoperiodic control of LH release in the ram. II. Light-androgens interaction
Pelletier, J.; Ortavant, R.
Acta Endocrinologica 78(3): 442-450
1975
ISSN/ISBN: 0001-5598 PMID: 1173013 Document Number: 83273
In experiment I, 2 groups of 15 castrated rams under 8 or 16 h illumination daily were slaughtered at different times after intramuscular injection of 200 mg testosterone propionate (TP). Animals receiving the vehicle only acted as controls. In both groups of rams, the LH concentration increased in the pituitary following TP treatment. A return to the pre-injection level was observed 48 h later only in animals under an 8-h light photoperiod, indicating a shorter negative effect of the injection than in the case of rams under a 16-h light photoperiod. In experiment II, the inhibitory effect of 300 and 600 mg TP was assessed by the decrease in the plasma LH level following an intramuscular injection. In both cases the decrease in LH release was more pronounced in rams under 16 h of daily illumination than in those under 8 h (mean decrease in LH release 21.2 and 33.2% resp. in 300- and 600-mg treated rams under 16 h daylight v 9.2 and 14.8% in rams under 8 h). It appears that steroid hormones modify the effect of photoperiod on hypothalamo-hypophyseal activity.