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Effect of castration of entire or cryptorchid rams on lh secretion
1600
I33 EFFECT Blanc*
OF CASTRATION OF ENTIRE OR CRYPTORCHID RAMS ON LH SECRETION. M.R ; & J.C. Poirier, Physiologie de la Reproduction 37380 NOUZILLY F.
We have previously given evidence for a testicular protein factor acting on LRF pulsatility ("LRF-STATIN") (Blanc Gal., 1981). We wanted to know the respective action of testicular steroids and "LRF-STATIN" in the feedback mechanism between testis and LH secretion. The effect of castration on the pulsatile secretion of LH has been compared in entire (E, n=5) and cryptorchid (C, n=5) rams. Blood was sampled every 15mn during 6hour at days (D) -1,+1,8,15,22 and 29 after castration. The LH pulse frequency was increased at D8 (number of LH pulses per 6hour period: 5.2+.4 vs 2.3+.4, x+s.e.m.) and further increased at D15 (7.2+.3) and D29 (8.7+.3) for E but was increased in only 1 out of 5 animals at D8 and in 4 out of 5 at D15 for C. LH pulse amplitude increased sharply at D+l (10.4+4.0 vs l+.lng/ml) further increased at D8 (15.7+1.7) and remained unchanged thereafter for E and was augmented at M-1 (23.ofl.O vs 15.4+2.0) and unchanged thereafter for C. During D-l, testosterone mean plasma levels were not different in E (3.0+.3) and C (5.5+1.4ng/ml) In the testes, the total amount of testosterone, 5dDHT and 17 (3 estradiol were 4200+1320, 124+18.4 and 15.8+lng for E and 16860+5040, 89.8+11.4, 14.8+1.6 for C respectively. We conclude that 1) the immediate effect of castration (O-8days) in the entire ram on LRF pulse frequency is not due to sexual steroids and could be attributed to a "LRF-STATIN" similar to that found in RTF, 2) the immediate effect of castration (O-2days) on amplitude of the LH pulses in the entire ram is to be attributed either to testicular steroids or to the interaction between sexual steroids and LRF-STATIN.
I34 OVARIAN OXYTOCIN. Animal Physiology,
E.L. Sheldrick* and A.P.F. Flint, AFRC Babraham, Cambridge, CB2 4AT.
Institute
of
The corpora lutea of the sheep, cow, goat, rabbit andmsncontain immunoIn contrast, noOT reactive oxytocin (OT) in concentrations up to 10 ug/g. has been found in corpora lutea of the rat or pig. Analytical methodsused mammary pressure and uterto identify luteal OT include radioimmunoassay, ine contractility bioassays, high performance liquid chromatography and fast-atom bombardment mass spectrometry; however, the sheep is the only In sheep the cells species in which all these methods have been applied. Measurements of OT in ovarian containing OT are the large lutein cells. venous plasma in sheep show that the corpora lutea secrete OT; peripheral OT concentrations change in parallel with those of progesterone, rising to Luteal 20-40 pg/ml plasma in the mid-luteal phase of the oestrous cycle. secretion is stimulated by the PGF2c analogue, cloprostenol. As in the neurohypophysis, OT is secreted from the corpus luteum with neurophysin OT is lost from the corpora lutea when luteal function is prolonged I/II. beyond the normal time of luteal regression (day 17 post-oestrus), as Since luteal progesterone prooccurs in pregnancy or after hysterectomy. duction is unchanged under these conditions it appears unlikely OT has any local action on steroid synthesis in the corpus luteum. Luteal OT may, however, be involved in controlling ovarian steroidogenesis by a systemic action, as immunization against OT delays luteal regression in cyclic sheep, and administration of OT shortens the cycle in cows and goats, proIndividual episodes of bably by stimulating uterine secretion of PGF2,. release of PGF2, and OT occurring simultaneously at luteal regression may involve a positive feedback loop.
I33 EFFECT Blanc*
OF CASTRATION OF ENTIRE OR CRYPTORCHID RAMS ON LH SECRETION. M.R ; & J.C. Poirier, Physiologie de la Reproduction 37380 NOUZILLY F.
We have previously given evidence for a testicular protein factor acting on LRF pulsatility ("LRF-STATIN") (Blanc Gal., 1981). We wanted to know the respective action of testicular steroids and "LRF-STATIN" in the feedback mechanism between testis and LH secretion. The effect of castration on the pulsatile secretion of LH has been compared in entire (E, n=5) and cryptorchid (C, n=5) rams. Blood was sampled every 15mn during 6hour at days (D) -1,+1,8,15,22 and 29 after castration. The LH pulse frequency was increased at D8 (number of LH pulses per 6hour period: 5.2+.4 vs 2.3+.4, x+s.e.m.) and further increased at D15 (7.2+.3) and D29 (8.7+.3) for E but was increased in only 1 out of 5 animals at D8 and in 4 out of 5 at D15 for C. LH pulse amplitude increased sharply at D+l (10.4+4.0 vs l+.lng/ml) further increased at D8 (15.7+1.7) and remained unchanged thereafter for E and was augmented at M-1 (23.ofl.O vs 15.4+2.0) and unchanged thereafter for C. During D-l, testosterone mean plasma levels were not different in E (3.0+.3) and C (5.5+1.4ng/ml) In the testes, the total amount of testosterone, 5dDHT and 17 (3 estradiol were 4200+1320, 124+18.4 and 15.8+lng for E and 16860+5040, 89.8+11.4, 14.8+1.6 for C respectively. We conclude that 1) the immediate effect of castration (O-8days) in the entire ram on LRF pulse frequency is not due to sexual steroids and could be attributed to a "LRF-STATIN" similar to that found in RTF, 2) the immediate effect of castration (O-2days) on amplitude of the LH pulses in the entire ram is to be attributed either to testicular steroids or to the interaction between sexual steroids and LRF-STATIN.
I34 OVARIAN OXYTOCIN. Animal Physiology,
E.L. Sheldrick* and A.P.F. Flint, AFRC Babraham, Cambridge, CB2 4AT.
Institute
of
The corpora lutea of the sheep, cow, goat, rabbit andmsncontain immunoIn contrast, noOT reactive oxytocin (OT) in concentrations up to 10 ug/g. has been found in corpora lutea of the rat or pig. Analytical methodsused mammary pressure and uterto identify luteal OT include radioimmunoassay, ine contractility bioassays, high performance liquid chromatography and fast-atom bombardment mass spectrometry; however, the sheep is the only In sheep the cells species in which all these methods have been applied. Measurements of OT in ovarian containing OT are the large lutein cells. venous plasma in sheep show that the corpora lutea secrete OT; peripheral OT concentrations change in parallel with those of progesterone, rising to Luteal 20-40 pg/ml plasma in the mid-luteal phase of the oestrous cycle. secretion is stimulated by the PGF2c analogue, cloprostenol. As in the neurohypophysis, OT is secreted from the corpus luteum with neurophysin OT is lost from the corpora lutea when luteal function is prolonged I/II. beyond the normal time of luteal regression (day 17 post-oestrus), as Since luteal progesterone prooccurs in pregnancy or after hysterectomy. duction is unchanged under these conditions it appears unlikely OT has any local action on steroid synthesis in the corpus luteum. Luteal OT may, however, be involved in controlling ovarian steroidogenesis by a systemic action, as immunization against OT delays luteal regression in cyclic sheep, and administration of OT shortens the cycle in cows and goats, proIndividual episodes of bably by stimulating uterine secretion of PGF2,. release of PGF2, and OT occurring simultaneously at luteal regression may involve a positive feedback loop.