Department of Anatomy, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, Texas 78284, USAO and Veteran Administration Hospital Endocrine and Polypeptide Lab and Department of Medicine, Tulane University, School of Medicine, New Orleans, La., USA2)
EFFECT OF D-Trp6-LH-RH ON THE PITUITARY-GONADAL AXIS DURING THE LUTEAL PHASE IN THE BABOON
By N. Hagino, O. Nakamoto, Y. Kunz, A. Arimura, D. H. Coy and A. V. Schally ABSTRACT An effect of D-Trp6-LH-RH (superactive LH-RH agonist) in the pituitary and ovarian function was examined. Four regularly cycling baboons were used for this study. After determination of control values of plasma levels of LH, oestrogen and progesterone during the entire menstrual cycle, D-Trp6-LH-RH was infused subcutaneously for 7 days during the early luteal phase in these four baboons. An infusion of D-Trp6-LH-RH increased plasma LH and oestrogen, but it failed to alter the plasma level of progesterone. From these results, it seems unlikely that 1) D\x=req-\ Trp6-LH-RH has a luteolytic effect, and 2) an increased ovarian oestrogen causes luteolysis in the baboon.
development of analogs of luteinizing hormone releasing hormone (LHRH) (Coy et al. 1976) prompted us to determine the effect of D-Trp6-LH-RH on the pituitary and ovarian function in baboons. Microinfusion of D-Trp6-LHRH (24 //g/kg body weight/24 h, 6 /.fg/24 h/rat) caused luteolysis in rats when applied after ovulation and blocked implantation of fertilized ova and sub¬ sequent gestation (Arimura et al., in press). Therefore, D-Trp6-LH-RH (24 /eg/ kg body weight/24 h; 480 /.cg/24 h/baboon) was infused subcutaneously during the luteal phase of the baboons, and plasma levels of progesterone as well as Recent
LH and oestrogen
were
determined.
MATERIALS AND METHODS In regularly cycling female baboons, blood was collected every other day through femoral puncture under light sedation (Ketamine hydrochloride, 10 mg/kg body weight, Bristol Lab, Syracuse, N.Y.). Light sedation does not interfer with the plasma levels of the LH, oestrogen and progesterone (Hagino 1974). Plasma levels of oestrogen, LH and progesterone were measured by radioimmunoassay, for an indicative of ovulation and functional luteinization (Hagino 1974). After determination of ovulation and functional luteinization, a superactive LH-RH agonist (D-Trp6-LH-RH; 24 «g/kg body weight/24 h: 9.9 «g/1 id, 0.9% saline solution/h: 480 «g/24 h/baboon) was infused sc using the microinfusion osmotic pump
(Alza, Palo Alto, California) for 7 days during the early luteal phase. Blood was col¬ lected every other day during the infusion and for another 5 days after cessation of the infusion.
O
18
(_>
14
?
El
2-
0
5
10
15
Days After D-Trp6-LHRH Administration
Figs.
1-3
show plasma levels of LH, oestrogen, and progesterone in control (O-O) baboons and in D-Trp6-LH-RH treated baboons (·-·). Vertical axis indicates plasma concentration of LH (ng/ml), oestrogen (pg/ml), or progesterone (ng/ml). Horizontal axis represents days after initiation of D-Trp6-LH-RH microinfusion (infusion was performed for 7 days) to the menses.
by double-antibody RIA methods. A used, and purified baboon LH was radioiodinated per tube and the intra- and interassay coefficients of variation of 70 per cent of the maximum binding were 4.7 and 9.5 per cent, respectively. Plasma LH assay was performed in the RIA Core in the Center lor Research in Reproductive Biology in the University (Pauerslein et al. 1978, supported by NIH Grant P30 HD 10202). Plasma LH.
Baboon LH
specific antibody generated —
Plasma progesterone.
was
determined
to baboon LH
A celite column
was
was
used for isolation of progesterone in
plasma. Plasma progesterone was determined by radioimmunoassay (Abraham et al. 1972). The coefficient of within assay variation was 7.90% in the range of 25 to 600 pg/tube. The sensitivity of the assay was 500 pg/ml in plasma. -
Plasma oestrogen. Total plasma oestrogen was determined by radioimmunoassay et al. 1972). The coefficient of within assay variation was 3.34 °/o in the range of 10 to 100 pg/tube. The sensitivity of the assay was 50 pg/ml in plasma. RIA assay for plasma progesterone and oestrogen was performed in our laboratory.
(Abraham
-
cr
(3| 200Q
D-Trp6-LHRH
0
5
10
Days After D-Trp6-LHRH Administration
Fig. 2.
RESULTS
Plasma LH. During luteal phase, the control values of plasma LH re¬ mained lower (mean and standard error in 4 baboons; 5.67 ± 1.00 ng/ml) (Fig. 1). An infusion of D-Trp6-LH-RH increased plasma levels of LH during the infusion (6.08 ± 3.25 vs 6.13 ± 2.10 ng/ml control; 23.15 ± 0.93 vs 6.88 ± 2.75; 15.12 ± 1.83 vs 2.37 ± 1.53; 14.70 ± 2.67 vs 8.36 ± 3.10; 13.22 ± 2.30 vs 2.93 ± 2.93 respectively). Six days after cessation of infusion, plasma LH re¬ turned to normal luteal value (5.50 ± 2.05 vs 6.69 ± 3.38 ng/ml control) (Fig. -
0· Plasma oestrogen. During luteal phase, the control values of plasma remained lower oestrogen (mean and standard error in 4 baboons; 8.15 ± 6.03 pg/ml) and there was no fluctuation or peak (Fig. 2). An infusion of D-Trp6LH-RH increased plasma levels of oestrogen during the luteal phase (114.23 ± 22.29 vs 91.23 ± 7.85 pg/ml control; 232.80 ± 9.80 vs 90.94 ± 9.06; 185.45 ± 43.05 vs 94.94 ± 15.77; 231.68 ±38.89 vs 119.91 ±28.50 respectively), and even though after cessation of the infusion plasma oestrogen remained higher (253.15 ± 55.64 vs 96.74 ± 18.27 ng/ml control; 237.13 ± 72.77 vs 103.38 ± -
19.60; 149.20 ± 91.81
vs
89.90 ± 11.77,
respectively) (Fig. 2).
£
1% if 9
D-Trp6-LHRH
— -1- ¬
5
10
Days After D-Trp6-LHRH Administration
Fig. 3.
Plasma progesterone. ovulation, and reached
-
a
Plasma progesterone was increased gradually after mid-luteal plateau (mean and standard error in 4
7.43 ± 0.82 ng/ml), and declined gradually to baseline value prior to menstruation (Fig. 3). An infusion of D-Trp6-LH-RH did not alter the plasma concentration of progesterone (3.95 ± 1.30 vs 4.45 ± 1.66 ng/ml control; 4.65 ± 0.87 vs 5.75 ± 1.94; 6.48 ± 0.91 vs 7.10 ± 0.82; 6.48 ± 0.31 vs 7.43 ± 0.82: 6.98 ± 0.39 vs 5.58 ± 1.44; 4.68 ± 0.45 vs 4.33 ± 0.82; 2.93 ± 1.48 vs 3.33 ±
baboons;
2.40,
respectively). DISCUSSION
Baboons showed
an
increased
(Hagino 1974; Koyama
plasma oestrogen
al. 1977; Pauerstein
and LH
et al.
prior
to ovulation
1978). Similar phenomena were observed in rhesus monkey (Karsch et cd. 1973; Hotchkiss el al. 1971) and human (Midglcy 8c Jaffe 1968; Van de Wiele et al. 1970; Abraham et al. 1972). In addition, plasma progesterone increased gradually after ovulation and reached a midluteal plateau and declined gradually to baseline value prior to menstruation (Fig. 3). Similar phenomena were observed in rhesus monkey (Monroe et al. 1970; Moudgal et al. 1972) and human (Johansson 1969; Abra¬ ham et al. 1972). However, in baboons plasma levels of oestrogen and LH remained lower values during the luteal phase (Figs. 1 and 2). LH acts as the luteotrophic hormone on the corpus luteum in the baboon (Hagino 1974; Hagino 8c Schally 1977); like in monkey (Nalbandov 8c Cook 1968; Knobil 1973; Moudgal et al. 1972) and in human (Van de Wiele et al. 1970). However, an increased plasma LH by sc infusion of D-Trp6-LH-RH in all four baboons did not increase the plasma level of progesterone (Fig. 3). Systemic administration of LH-RH agonist ([D-Leu6, Des-Gly-NH210] LH-RH, Anchar et al. 1977«), causes a reduction of LH receptors in the male gonads. Supplementing these results, progesterone has a negative regulatory system of progesterone synthesis from the cholesterol (Haksar et al. 1967). Therefore, it seems likely that a negative regulatory system of LH receptors as well as progesterone production in the corpus luteum may prevent the over production of progesterone by an excessive amount of circulating LH. In rats, chronic sc infusion of D-Trpö-LH-RH suppressed luteal function and blocked a nidation (Arimura et al., in press), however, in baboons, it failed to show any luteolytic effect of D-Trp6-LH-RH. The differences could be due to the species differences. Another evidence was found that all four baboons receiving the infusion of D-Trp6-LH-RH demonstrated an increased plasma oestrogen (endogenous oestrogen). An increased oestrogen in circulation by administration of oestradiol benzoate during the luteal phase in baboons suppressed plasma level of progeset
tin, and failed to return to the control value even though after cessation of oestrogen administration (Hagino, submitted for publication). Similar pheno¬ mena were observed in the rhesus monkey (Knobil 1973) and in human (Board et al. 1973; Gore et al. 1973; Johansson 8c Gemzell 1971). A luteolytic effect of administered oestrogen reflects mainly a direct action of oestrogen on the uterus in human (Denamur 8c Kann 1973), but not in rhesus monkey; selfproduced oestrogen in the corpus luteum (Savard et al. 1965) leads to its own demise of the corpus luteum (Knobil 1973). However, in this experiment, an increased ovarian oestrogen in circulation did not suppress the functional luteinization. An explanation may be that an excessive amount of LH in plasma which was produced by D-Trp6-LH-RH infusion overrides the luteo¬ lytic effect of ovarian produced oestrogen. However, previous study with baboons indicates that administered oestrogen suppressed the functional luteini¬ zation strikingly, even though plasma LH was elevated extensively (Hagino, submitted for publication), and further, the inhibitory action of administered on progesterone secretion was not associated always with a reduction in circulating LH levels (Karsch et al. 1973). Supplementing these observations ovarian LH/hCG receptors in cultured follicles have been shown to become relractory to further ovine LH stimulation following an initial exposure to ovine LH (Lamprecht et al. 1973), while LH has also been implicated in the loss of LH-receptors during luteinization (Richards 8c Midgley 1976). Further¬ more, systemic administration of LH (Anclair et al. 19770; Hsueh et al. 1976;
oestrogen
Sharpe 1976)
LH-RH agonist (Anclair et al. 1977a) caused a reduction of LH receptors in male gonads. Therefore, it seems unlikely that the excessive amount of plasma LH overcomes the luteolytic effect of oestrogen. A possible consideration may be that an endogenous oestrogen produced in the ovary may not have a luteolytic effect like that was found in the admi¬ nistered oestradiol benzoate. or
ACKNOWLEDGMENTS This study was supported by NIH Grant NICHD-10071. Plasma LH was determined in RIA Core Facility in NICHD Center for Research in Reproductive Biology (Sup¬ ported NIH Grant P30 HD 10202).
REFERENCES Abraham G. £., Odell W. D.,
Swerdlolf R. S. & Hopper
K.:
J.
clin. Endocr. 34
(1972)
312.
Anclair C,
(1977«)
Kelly
P.
1890.
., Coy D. H., Schally A. V. & Labrie F.: Endocrinology
101
Anclair C, Kelly P. ., Labrie F., Coy D. H. 8c Schally A. V'.: Biochem. biophys. Res. Commun. 76
(19776)
855.
Board J. .. Bhatnagar A. S. 8- Bush C. W.: Fértil and Steril. 24 (1973) 95. Coy D. H., Vilchez-Martinez J. ., Coy . J. 8- Schally . V'..· J. med. Chem.
(1976)
19
423. Denamur R. & Kann G.: Acta endocr. (Kbh.) 73 (1973) 635. Gore B. S.. Caldwell B. W. & Speroff L.: J. clin. Endocr. 36 (1973) 615. Hagino N. In: Coutinho E. M. and Fuchs F., Eds. Follicular Maturation, Ovulation, Luteinization and Menstruation in the Baboon. Physiology and Genetics of Reproduc¬ tion. Part A, (1974) pp. 323-342. Hagino N. & Schally A. V'..· Horm. Metab. Res. 9 (1977) 253. Haksar ., Romanoff E. B., Hagino N. 8c Pincus G.: Steroids 9 (1967) 405. Holchkiss ]., Atkinson L. E. 8c Knobil E.: Endocrinology 89 (1971) 177. Hsueh A. J. W.. Dufan M. L. & Catt K. J.: Biochem. biophys. Res. Commun. 72 (1976) 1145.
Johansson E. D. B.: Acta endocr. (Kbh.) 61 (1969) 592. Johansson E. D. B. 8c Gemzell C: Acta endocr. (Kbh.) 68 (1971) 551. Karsch F. J., Dieschke D. J. Weick R. F., Yamaji T., Hotchkiss J. & Knobil E.: Endo¬ crinology 92 (1973) 799. Knobil E.: Biol. Reprod. 8 (1973) 246. Koyama T., de la Pena A. 8c Hagino .: Amer. J. Obstet. Gynec. 127 (1977) 67. Lamprecht S. ., Sar U., Tsafriis A. 8c Lindner H. R.: J. Endocr. 57 (1973) 217. Midgley A. R. 8c Jaffe R. B.: J. clin. Endocr. 28 (1968) 1699. Monroe S. E., Atkinson L. E 8c Knobil E.: Endocrinology 87 (1970) 453. Moudgal N. R., MacDonald G. J. Greep G. J.: J. clin. Endocr. 35 (1972) 113. Nalbandov A. V. 8c Cook B.: Ann. Rev. Physiol. 30 (1968) 245. Pauerstein C. J., Eddy C. ., Croxatto H. D., Hess R., Siler-Khodr T. M. & Croxatto H. B.: Amer. J. Obstet. Gynec. 130 (1978) 876. Richards J. S. 8c Midgley A. R. Jr.: Biol. Reprod. 14 (1976) 82. Savard K., Marsch J. M. 8c Rice B. F.: Recent Progr. Hormone Res. 21 (1965) 285.
Sharpe
R. M.: Nature (Lond.) 264 (1976) 644. Van de Wiele R. L., Bogumil J., Dyrenfurth L, Ferin M., Jewelewicz R., Warren M., Rizkallah T. 8c Mikhail G.: Recent Progr. Hormone Res. 26 (1970) 63.
Received
on
September 25th,
1978.
EFFECT OF D-Trp6-LH-RH ON THE PITUITARY-GONADAL AXIS DURING THE LUTEAL PHASE IN THE BABOON
By N. Hagino, O. Nakamoto, Y. Kunz, A. Arimura, D. H. Coy and A. V. Schally ABSTRACT An effect of D-Trp6-LH-RH (superactive LH-RH agonist) in the pituitary and ovarian function was examined. Four regularly cycling baboons were used for this study. After determination of control values of plasma levels of LH, oestrogen and progesterone during the entire menstrual cycle, D-Trp6-LH-RH was infused subcutaneously for 7 days during the early luteal phase in these four baboons. An infusion of D-Trp6-LH-RH increased plasma LH and oestrogen, but it failed to alter the plasma level of progesterone. From these results, it seems unlikely that 1) D\x=req-\ Trp6-LH-RH has a luteolytic effect, and 2) an increased ovarian oestrogen causes luteolysis in the baboon.
development of analogs of luteinizing hormone releasing hormone (LHRH) (Coy et al. 1976) prompted us to determine the effect of D-Trp6-LH-RH on the pituitary and ovarian function in baboons. Microinfusion of D-Trp6-LHRH (24 //g/kg body weight/24 h, 6 /.fg/24 h/rat) caused luteolysis in rats when applied after ovulation and blocked implantation of fertilized ova and sub¬ sequent gestation (Arimura et al., in press). Therefore, D-Trp6-LH-RH (24 /eg/ kg body weight/24 h; 480 /.cg/24 h/baboon) was infused subcutaneously during the luteal phase of the baboons, and plasma levels of progesterone as well as Recent
LH and oestrogen
were
determined.
MATERIALS AND METHODS In regularly cycling female baboons, blood was collected every other day through femoral puncture under light sedation (Ketamine hydrochloride, 10 mg/kg body weight, Bristol Lab, Syracuse, N.Y.). Light sedation does not interfer with the plasma levels of the LH, oestrogen and progesterone (Hagino 1974). Plasma levels of oestrogen, LH and progesterone were measured by radioimmunoassay, for an indicative of ovulation and functional luteinization (Hagino 1974). After determination of ovulation and functional luteinization, a superactive LH-RH agonist (D-Trp6-LH-RH; 24 «g/kg body weight/24 h: 9.9 «g/1 id, 0.9% saline solution/h: 480 «g/24 h/baboon) was infused sc using the microinfusion osmotic pump
(Alza, Palo Alto, California) for 7 days during the early luteal phase. Blood was col¬ lected every other day during the infusion and for another 5 days after cessation of the infusion.
O
18
(_>
14
?
El
2-
0
5
10
15
Days After D-Trp6-LHRH Administration
Figs.
1-3
show plasma levels of LH, oestrogen, and progesterone in control (O-O) baboons and in D-Trp6-LH-RH treated baboons (·-·). Vertical axis indicates plasma concentration of LH (ng/ml), oestrogen (pg/ml), or progesterone (ng/ml). Horizontal axis represents days after initiation of D-Trp6-LH-RH microinfusion (infusion was performed for 7 days) to the menses.
by double-antibody RIA methods. A used, and purified baboon LH was radioiodinated per tube and the intra- and interassay coefficients of variation of 70 per cent of the maximum binding were 4.7 and 9.5 per cent, respectively. Plasma LH assay was performed in the RIA Core in the Center lor Research in Reproductive Biology in the University (Pauerslein et al. 1978, supported by NIH Grant P30 HD 10202). Plasma LH.
Baboon LH
specific antibody generated —
Plasma progesterone.
was
determined
to baboon LH
A celite column
was
was
used for isolation of progesterone in
plasma. Plasma progesterone was determined by radioimmunoassay (Abraham et al. 1972). The coefficient of within assay variation was 7.90% in the range of 25 to 600 pg/tube. The sensitivity of the assay was 500 pg/ml in plasma. -
Plasma oestrogen. Total plasma oestrogen was determined by radioimmunoassay et al. 1972). The coefficient of within assay variation was 3.34 °/o in the range of 10 to 100 pg/tube. The sensitivity of the assay was 50 pg/ml in plasma. RIA assay for plasma progesterone and oestrogen was performed in our laboratory.
(Abraham
-
cr
(3| 200Q
D-Trp6-LHRH
0
5
10
Days After D-Trp6-LHRH Administration
Fig. 2.
RESULTS
Plasma LH. During luteal phase, the control values of plasma LH re¬ mained lower (mean and standard error in 4 baboons; 5.67 ± 1.00 ng/ml) (Fig. 1). An infusion of D-Trp6-LH-RH increased plasma levels of LH during the infusion (6.08 ± 3.25 vs 6.13 ± 2.10 ng/ml control; 23.15 ± 0.93 vs 6.88 ± 2.75; 15.12 ± 1.83 vs 2.37 ± 1.53; 14.70 ± 2.67 vs 8.36 ± 3.10; 13.22 ± 2.30 vs 2.93 ± 2.93 respectively). Six days after cessation of infusion, plasma LH re¬ turned to normal luteal value (5.50 ± 2.05 vs 6.69 ± 3.38 ng/ml control) (Fig. -
0· Plasma oestrogen. During luteal phase, the control values of plasma remained lower oestrogen (mean and standard error in 4 baboons; 8.15 ± 6.03 pg/ml) and there was no fluctuation or peak (Fig. 2). An infusion of D-Trp6LH-RH increased plasma levels of oestrogen during the luteal phase (114.23 ± 22.29 vs 91.23 ± 7.85 pg/ml control; 232.80 ± 9.80 vs 90.94 ± 9.06; 185.45 ± 43.05 vs 94.94 ± 15.77; 231.68 ±38.89 vs 119.91 ±28.50 respectively), and even though after cessation of the infusion plasma oestrogen remained higher (253.15 ± 55.64 vs 96.74 ± 18.27 ng/ml control; 237.13 ± 72.77 vs 103.38 ± -
19.60; 149.20 ± 91.81
vs
89.90 ± 11.77,
respectively) (Fig. 2).
£
1% if 9
D-Trp6-LHRH
— -1- ¬
5
10
Days After D-Trp6-LHRH Administration
Fig. 3.
Plasma progesterone. ovulation, and reached
-
a
Plasma progesterone was increased gradually after mid-luteal plateau (mean and standard error in 4
7.43 ± 0.82 ng/ml), and declined gradually to baseline value prior to menstruation (Fig. 3). An infusion of D-Trp6-LH-RH did not alter the plasma concentration of progesterone (3.95 ± 1.30 vs 4.45 ± 1.66 ng/ml control; 4.65 ± 0.87 vs 5.75 ± 1.94; 6.48 ± 0.91 vs 7.10 ± 0.82; 6.48 ± 0.31 vs 7.43 ± 0.82: 6.98 ± 0.39 vs 5.58 ± 1.44; 4.68 ± 0.45 vs 4.33 ± 0.82; 2.93 ± 1.48 vs 3.33 ±
baboons;
2.40,
respectively). DISCUSSION
Baboons showed
an
increased
(Hagino 1974; Koyama
plasma oestrogen
al. 1977; Pauerstein
and LH
et al.
prior
to ovulation
1978). Similar phenomena were observed in rhesus monkey (Karsch et cd. 1973; Hotchkiss el al. 1971) and human (Midglcy 8c Jaffe 1968; Van de Wiele et al. 1970; Abraham et al. 1972). In addition, plasma progesterone increased gradually after ovulation and reached a midluteal plateau and declined gradually to baseline value prior to menstruation (Fig. 3). Similar phenomena were observed in rhesus monkey (Monroe et al. 1970; Moudgal et al. 1972) and human (Johansson 1969; Abra¬ ham et al. 1972). However, in baboons plasma levels of oestrogen and LH remained lower values during the luteal phase (Figs. 1 and 2). LH acts as the luteotrophic hormone on the corpus luteum in the baboon (Hagino 1974; Hagino 8c Schally 1977); like in monkey (Nalbandov 8c Cook 1968; Knobil 1973; Moudgal et al. 1972) and in human (Van de Wiele et al. 1970). However, an increased plasma LH by sc infusion of D-Trp6-LH-RH in all four baboons did not increase the plasma level of progesterone (Fig. 3). Systemic administration of LH-RH agonist ([D-Leu6, Des-Gly-NH210] LH-RH, Anchar et al. 1977«), causes a reduction of LH receptors in the male gonads. Supplementing these results, progesterone has a negative regulatory system of progesterone synthesis from the cholesterol (Haksar et al. 1967). Therefore, it seems likely that a negative regulatory system of LH receptors as well as progesterone production in the corpus luteum may prevent the over production of progesterone by an excessive amount of circulating LH. In rats, chronic sc infusion of D-Trpö-LH-RH suppressed luteal function and blocked a nidation (Arimura et al., in press), however, in baboons, it failed to show any luteolytic effect of D-Trp6-LH-RH. The differences could be due to the species differences. Another evidence was found that all four baboons receiving the infusion of D-Trp6-LH-RH demonstrated an increased plasma oestrogen (endogenous oestrogen). An increased oestrogen in circulation by administration of oestradiol benzoate during the luteal phase in baboons suppressed plasma level of progeset
tin, and failed to return to the control value even though after cessation of oestrogen administration (Hagino, submitted for publication). Similar pheno¬ mena were observed in the rhesus monkey (Knobil 1973) and in human (Board et al. 1973; Gore et al. 1973; Johansson 8c Gemzell 1971). A luteolytic effect of administered oestrogen reflects mainly a direct action of oestrogen on the uterus in human (Denamur 8c Kann 1973), but not in rhesus monkey; selfproduced oestrogen in the corpus luteum (Savard et al. 1965) leads to its own demise of the corpus luteum (Knobil 1973). However, in this experiment, an increased ovarian oestrogen in circulation did not suppress the functional luteinization. An explanation may be that an excessive amount of LH in plasma which was produced by D-Trp6-LH-RH infusion overrides the luteo¬ lytic effect of ovarian produced oestrogen. However, previous study with baboons indicates that administered oestrogen suppressed the functional luteini¬ zation strikingly, even though plasma LH was elevated extensively (Hagino, submitted for publication), and further, the inhibitory action of administered on progesterone secretion was not associated always with a reduction in circulating LH levels (Karsch et al. 1973). Supplementing these observations ovarian LH/hCG receptors in cultured follicles have been shown to become relractory to further ovine LH stimulation following an initial exposure to ovine LH (Lamprecht et al. 1973), while LH has also been implicated in the loss of LH-receptors during luteinization (Richards 8c Midgley 1976). Further¬ more, systemic administration of LH (Anclair et al. 19770; Hsueh et al. 1976;
oestrogen
Sharpe 1976)
LH-RH agonist (Anclair et al. 1977a) caused a reduction of LH receptors in male gonads. Therefore, it seems unlikely that the excessive amount of plasma LH overcomes the luteolytic effect of oestrogen. A possible consideration may be that an endogenous oestrogen produced in the ovary may not have a luteolytic effect like that was found in the admi¬ nistered oestradiol benzoate. or
ACKNOWLEDGMENTS This study was supported by NIH Grant NICHD-10071. Plasma LH was determined in RIA Core Facility in NICHD Center for Research in Reproductive Biology (Sup¬ ported NIH Grant P30 HD 10202).
REFERENCES Abraham G. £., Odell W. D.,
Swerdlolf R. S. & Hopper
K.:
J.
clin. Endocr. 34
(1972)
312.
Anclair C,
(1977«)
Kelly
P.
1890.
., Coy D. H., Schally A. V. & Labrie F.: Endocrinology
101
Anclair C, Kelly P. ., Labrie F., Coy D. H. 8c Schally A. V'.: Biochem. biophys. Res. Commun. 76
(19776)
855.
Board J. .. Bhatnagar A. S. 8- Bush C. W.: Fértil and Steril. 24 (1973) 95. Coy D. H., Vilchez-Martinez J. ., Coy . J. 8- Schally . V'..· J. med. Chem.
(1976)
19
423. Denamur R. & Kann G.: Acta endocr. (Kbh.) 73 (1973) 635. Gore B. S.. Caldwell B. W. & Speroff L.: J. clin. Endocr. 36 (1973) 615. Hagino N. In: Coutinho E. M. and Fuchs F., Eds. Follicular Maturation, Ovulation, Luteinization and Menstruation in the Baboon. Physiology and Genetics of Reproduc¬ tion. Part A, (1974) pp. 323-342. Hagino N. & Schally A. V'..· Horm. Metab. Res. 9 (1977) 253. Haksar ., Romanoff E. B., Hagino N. 8c Pincus G.: Steroids 9 (1967) 405. Holchkiss ]., Atkinson L. E. 8c Knobil E.: Endocrinology 89 (1971) 177. Hsueh A. J. W.. Dufan M. L. & Catt K. J.: Biochem. biophys. Res. Commun. 72 (1976) 1145.
Johansson E. D. B.: Acta endocr. (Kbh.) 61 (1969) 592. Johansson E. D. B. 8c Gemzell C: Acta endocr. (Kbh.) 68 (1971) 551. Karsch F. J., Dieschke D. J. Weick R. F., Yamaji T., Hotchkiss J. & Knobil E.: Endo¬ crinology 92 (1973) 799. Knobil E.: Biol. Reprod. 8 (1973) 246. Koyama T., de la Pena A. 8c Hagino .: Amer. J. Obstet. Gynec. 127 (1977) 67. Lamprecht S. ., Sar U., Tsafriis A. 8c Lindner H. R.: J. Endocr. 57 (1973) 217. Midgley A. R. 8c Jaffe R. B.: J. clin. Endocr. 28 (1968) 1699. Monroe S. E., Atkinson L. E 8c Knobil E.: Endocrinology 87 (1970) 453. Moudgal N. R., MacDonald G. J. Greep G. J.: J. clin. Endocr. 35 (1972) 113. Nalbandov A. V. 8c Cook B.: Ann. Rev. Physiol. 30 (1968) 245. Pauerstein C. J., Eddy C. ., Croxatto H. D., Hess R., Siler-Khodr T. M. & Croxatto H. B.: Amer. J. Obstet. Gynec. 130 (1978) 876. Richards J. S. 8c Midgley A. R. Jr.: Biol. Reprod. 14 (1976) 82. Savard K., Marsch J. M. 8c Rice B. F.: Recent Progr. Hormone Res. 21 (1965) 285.
Sharpe
R. M.: Nature (Lond.) 264 (1976) 644. Van de Wiele R. L., Bogumil J., Dyrenfurth L, Ferin M., Jewelewicz R., Warren M., Rizkallah T. 8c Mikhail G.: Recent Progr. Hormone Res. 26 (1970) 63.
Received
on
September 25th,
1978.
