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Prostaglandins and catecholamines in gonadtropin secretion
PROSTAGLANDINS
LETTER
PROSTAGLANDINS
TO THE
AND
GONADOTROPIN
EDITOR
CATECHOLAMINES
IN
SECRETION
Gentlemen, I was quite interested in a recent comment of Patron0 and Serta (1) on the failure of indomethacin treatment to block the response of the pituitary gland in man to exogenous LRI?. As their comanent was prompted by our earlier paper (2), it is perhaps not inappropriate to discuss some aspects of our study. This particular study dealt with the possible role of PGF in potentiating adrenergic transmission, which is known to be involved in gonadotropin secretion (3).
The hypothesis was tested in McCormack-
Meyer model which involves use of 26-day-old immature rats primed with 5 i.u. of PMS and given a single subcutaneous injection of progesterone 24 hr later (4). While the dose of PMS is inadequate to induce ovulation by itself, subsequent injection of progesterone evokes full ovulatory response (4).
This facilitator-yaction of progesterone is media-
ted via a-adrenergic pathway in the hypothalamus as intraventricular injection of phenoxybenzamine-an a-adrenergic blocker, can block ovulation (5) and increased LH secretion (6). Thus the model is ideally suited for the test of our hypothesis.
It was found that bilateral
injections of aspirin into the anterior hypothalamic area (AHA) at about the time of onset of the critical period blocked the facilitatory effect of progesterone; but microinjection of vehicle above did not (2).
OCTOBER
However, simultaneous injection of PGF2a or dopamine into
10, 1974
VOL. 8 NO. 1
79
PROSTAGLANDINS
ARA fully restored ovulation blocked by aspirin (2). We interpreted these results to mean that PGs and catecholamines (CA) may interact to potentiate adrenergic transmission known to be normally required for gonadotropin secretion (3). Before undertaking the above experiments, we injected aspirin into the 3rd ventricle prior to the onset of the critical period on the day of progesterone injection in the McCormack-Meyer model.
Results
of this experiment proved uniformly negative and, therefore, were not included in our published report (2). However, the negative results suggest that aspirin in the dose used (60-100 ug) failed to diffuse in an effective quantity from the 3rd ventricle to suppress PG synthesis in the relevant area of the hypothalamus, i.e. APIA,where presumably CA fibres most likely form synapses with LRP secreting neurons (12). Thus it is not surprising that the peripherally administered indomethacin failed to affect LH secretion in the experiments of Patron0 and Serra (1).
Indeed in several experiments it has been
shown that parenterally administered indomethacin interferes with spontaneous ovulation primarily by acting on the ovary as exogenous gonadotropins could not reverse the effect of the inhibitor (7, 8, 9) and LH surge on the day of proestrus occurred normally despite the inhibition of ovulation (10). Thus none of these studies exclude the possible role of hypothalamic and/or pituitary PGs in gonadotropin secretion as subcutaneously administered indomethacin may be more effective in inhibiting PG synthesis in the ovary than in the hypothalamus possibly due to differential sensitivity of these tissues and/or poor penetration of the drug across the blood-brain barrier.
80
OCTOBER
10, 1974
VOL. 8 NO. 1
PROSTAGLANDINS
Significantly none of these studies included measurements of hypothalamic PG levels following administration of indomethacin.
However,
Behrman et al. (11) did report decreases in hypothalamic-pituitary levels of PGs in immature rats in which gonadotropically induced ovulation was blocked by subcutaneous injection of aspirin; administration of LRP or LH restored ovulation in such rats suggesting the possible central site of action of aspirin, a fact confirmed later in our study (2). Thus one implication of the negative results of Patron0 and Serra (1) and those of others is that peripheral route of administration of inhibitors of PG biosynthesis cannot always be used to demonstrate the role of hypothalamic or pituitary PGs in gonadotropin secretion. For this purpose those agents must be administered locally within the hypothalamus or pituitary gland.
However, problems inherent in such
an approach should not be forgotten.
One of the problems is the
possibility that the inhibitor may not act at the site of injection, i.e. AHA, but may diffuse to other areas such as the median eminence and from there through the portal circulation to the anterior pituitary. This problem in our experiments was minimized by the demonstration that the intrapituitary injection of aspirin failed to interfere with progesterone-induced ovulation (2). The other problem concerns the reversal experiment.
As already
stated, dopamine was dissolved in the same common solution as aspirin to reverse the inhibitory effect of the latter.
It can be argued
that dopamine by combining in some way with aspirin may have rendered it ineffective in inhibiting ovulation.
OCTOBER
10, 1974
VOL. 8 NO. 1
However, we have observed
81
PROSTAGLANDINS
that dopamine can reverse the inhibitory effects of serotonin (5) and reserpine (Zolovick and Labhsetwar, unpublished observations) under identical conditions.
Thus while the possibility of dopamine combin-
ing with aspirin, serotonin or reserpine and rendering it ineffective when administered together cannot be completely ruled out, it appears remote as dopamine was capable of reversing inhibitory effects of 3 different chemically unrelated compounds.
A. P. Labhsetwar, Ph.D. Division of Biology Kansas State University Manhattan, Kansas 66506
1.
Patrono, C. and Serra, G.
(1974)
Prostaglandins 6, 345.
2.
Labhsetwar, A. P. and Zolovick, A. 249, 55.
3.
McCann, S., Krulich, L., Cooper, K., Kalra, P., Kalra, S., Libertuu, C., Negro-Vilar, A., Orias, R., Ronnekleiv, O., and Fawcett, C. (1973) 2. Reprod. Fert. Suppl. 20, 43.
4.
McCormack, C. E. and Meyer, R. K. 3, 300.
5.
Zolovick, A. and Labhsetwar, A. P. 245, 158.
6.
Kalra, P., Kalra, S., Krulich, L., Fawcett, C. and McCann, S. (1972) Endocrinology 90, 1168.
7.
Armstrong, A., Moon, Y. S. and Grinwich, D. science 9, 709.
8.
Tsafriri, A., Lindner, ?I.,Zor, U. and Lamprecht, S. Prostaglandins 2, 1.
9.
Saksena, S. K., Lau, I. and Shaikh, A. 25, 636.
(1973) Nature (&
Biology)
(1963) -Gen. and Camp. Endocr.
(1973) Nature (NaJ Biology)
(1973) -Adv. Bio-
(1972)
(1974) -Fert. Steril.
OCTOBER
10,1974 VOL. 8 NO. 1
PROSTAGLANDINS
10.
Sato, T., Taya, K., Fert. 39, 33.
11.
Behrman, H., Orczyk, G. P. and Greep, R. 1, 245.
12.
Kalra, S. P. and McCann, S.
Jyujo, T. and Igarashi, M.
(1973)
(1974) 2. Reprod.
(1972) Prostaglandins
Endocrinology 93, 356.
COMMENT Dr. Labhsetwar's discussion is most relevant to the interpretation of that portion of our data (1) indicating the failure of indomethacin treatment to appreciably reduce basal LH levels, which are obviously a reflection of both hypothalamic and pituitary activity. As for the question of the possible physiologic role of pituitary PGs in LRF-stimulated gonadotropin secretion and the relevance of our negative findings to it, we have now preliminary evidence to suggest that the POsynthetase of human pituitary has a lower sensitivity to the inhibitory action of non-steroid anti-inflammatory drugs as compared to other tissues. In a few experiments so far completed, the release of PGF -as measured by radioimmunoassay (2)- from fragments of human pitul*Z" ary tissue studied in vitro with the technique of continuous superfusion (3) is only slightly inhibited by the same concentration of drug capable of completely suppressing its release from the rat uterus and rabbit platelets (Patrono, Ciabattoni and Serra, unpublished experiments). Moreover, any interpretation of the effects of anti-inflammatory drugs should now take into account the recent observation of Mandel and Kuehl that indomethacin is a potent inhibitor of phosphodiesterase (4). If pituitary PGs do indeed mediate LRF-induced cyclic AMP formation and LH release, a combination of uncompletely depressed PG synthesis and of possibly inhibited phosphodiesterase activity is perhaps adequate to explain our negative results. In addition, this might account for the absence of dramatic endocrine changes in people undergoing chronic treatment with this family of drugs. C. Patrono, M.D. Dept. of Pharmacology Universitl Cattolica S. Cuore 00168 Rome, Italy
OCTOBER
10, 1974
VOL. 8 NO. 1
83
PROSTAGLANDINS
REFERENCES 1. Patrono, C. and Serra, G.B., Prostaglandins 6: 345, 1974. 2. Patrono, C. and Ciabattoni, G., in "Radioimmunoassay and Related Procedures in Medicine" vol. I: 451, International Atomic Energy Agency, Vienna, 1974. 3. Serra, G.B. and Midgley, A.R.Jr., Proc.Soc.Exp.Biol.Med. 133: 1370, 1970. 4. Kuehl, F.A.Jr., Prostaglandins 5: 325, 1974.
84
OCTOBER
10, 1974
VOL. 8 NO. 1
LETTER
PROSTAGLANDINS
TO THE
AND
GONADOTROPIN
EDITOR
CATECHOLAMINES
IN
SECRETION
Gentlemen, I was quite interested in a recent comment of Patron0 and Serta (1) on the failure of indomethacin treatment to block the response of the pituitary gland in man to exogenous LRI?. As their comanent was prompted by our earlier paper (2), it is perhaps not inappropriate to discuss some aspects of our study. This particular study dealt with the possible role of PGF in potentiating adrenergic transmission, which is known to be involved in gonadotropin secretion (3).
The hypothesis was tested in McCormack-
Meyer model which involves use of 26-day-old immature rats primed with 5 i.u. of PMS and given a single subcutaneous injection of progesterone 24 hr later (4). While the dose of PMS is inadequate to induce ovulation by itself, subsequent injection of progesterone evokes full ovulatory response (4).
This facilitator-yaction of progesterone is media-
ted via a-adrenergic pathway in the hypothalamus as intraventricular injection of phenoxybenzamine-an a-adrenergic blocker, can block ovulation (5) and increased LH secretion (6). Thus the model is ideally suited for the test of our hypothesis.
It was found that bilateral
injections of aspirin into the anterior hypothalamic area (AHA) at about the time of onset of the critical period blocked the facilitatory effect of progesterone; but microinjection of vehicle above did not (2).
OCTOBER
However, simultaneous injection of PGF2a or dopamine into
10, 1974
VOL. 8 NO. 1
79
PROSTAGLANDINS
ARA fully restored ovulation blocked by aspirin (2). We interpreted these results to mean that PGs and catecholamines (CA) may interact to potentiate adrenergic transmission known to be normally required for gonadotropin secretion (3). Before undertaking the above experiments, we injected aspirin into the 3rd ventricle prior to the onset of the critical period on the day of progesterone injection in the McCormack-Meyer model.
Results
of this experiment proved uniformly negative and, therefore, were not included in our published report (2). However, the negative results suggest that aspirin in the dose used (60-100 ug) failed to diffuse in an effective quantity from the 3rd ventricle to suppress PG synthesis in the relevant area of the hypothalamus, i.e. APIA,where presumably CA fibres most likely form synapses with LRP secreting neurons (12). Thus it is not surprising that the peripherally administered indomethacin failed to affect LH secretion in the experiments of Patron0 and Serra (1).
Indeed in several experiments it has been
shown that parenterally administered indomethacin interferes with spontaneous ovulation primarily by acting on the ovary as exogenous gonadotropins could not reverse the effect of the inhibitor (7, 8, 9) and LH surge on the day of proestrus occurred normally despite the inhibition of ovulation (10). Thus none of these studies exclude the possible role of hypothalamic and/or pituitary PGs in gonadotropin secretion as subcutaneously administered indomethacin may be more effective in inhibiting PG synthesis in the ovary than in the hypothalamus possibly due to differential sensitivity of these tissues and/or poor penetration of the drug across the blood-brain barrier.
80
OCTOBER
10, 1974
VOL. 8 NO. 1
PROSTAGLANDINS
Significantly none of these studies included measurements of hypothalamic PG levels following administration of indomethacin.
However,
Behrman et al. (11) did report decreases in hypothalamic-pituitary levels of PGs in immature rats in which gonadotropically induced ovulation was blocked by subcutaneous injection of aspirin; administration of LRP or LH restored ovulation in such rats suggesting the possible central site of action of aspirin, a fact confirmed later in our study (2). Thus one implication of the negative results of Patron0 and Serra (1) and those of others is that peripheral route of administration of inhibitors of PG biosynthesis cannot always be used to demonstrate the role of hypothalamic or pituitary PGs in gonadotropin secretion. For this purpose those agents must be administered locally within the hypothalamus or pituitary gland.
However, problems inherent in such
an approach should not be forgotten.
One of the problems is the
possibility that the inhibitor may not act at the site of injection, i.e. AHA, but may diffuse to other areas such as the median eminence and from there through the portal circulation to the anterior pituitary. This problem in our experiments was minimized by the demonstration that the intrapituitary injection of aspirin failed to interfere with progesterone-induced ovulation (2). The other problem concerns the reversal experiment.
As already
stated, dopamine was dissolved in the same common solution as aspirin to reverse the inhibitory effect of the latter.
It can be argued
that dopamine by combining in some way with aspirin may have rendered it ineffective in inhibiting ovulation.
OCTOBER
10, 1974
VOL. 8 NO. 1
However, we have observed
81
PROSTAGLANDINS
that dopamine can reverse the inhibitory effects of serotonin (5) and reserpine (Zolovick and Labhsetwar, unpublished observations) under identical conditions.
Thus while the possibility of dopamine combin-
ing with aspirin, serotonin or reserpine and rendering it ineffective when administered together cannot be completely ruled out, it appears remote as dopamine was capable of reversing inhibitory effects of 3 different chemically unrelated compounds.
A. P. Labhsetwar, Ph.D. Division of Biology Kansas State University Manhattan, Kansas 66506
1.
Patrono, C. and Serra, G.
(1974)
Prostaglandins 6, 345.
2.
Labhsetwar, A. P. and Zolovick, A. 249, 55.
3.
McCann, S., Krulich, L., Cooper, K., Kalra, P., Kalra, S., Libertuu, C., Negro-Vilar, A., Orias, R., Ronnekleiv, O., and Fawcett, C. (1973) 2. Reprod. Fert. Suppl. 20, 43.
4.
McCormack, C. E. and Meyer, R. K. 3, 300.
5.
Zolovick, A. and Labhsetwar, A. P. 245, 158.
6.
Kalra, P., Kalra, S., Krulich, L., Fawcett, C. and McCann, S. (1972) Endocrinology 90, 1168.
7.
Armstrong, A., Moon, Y. S. and Grinwich, D. science 9, 709.
8.
Tsafriri, A., Lindner, ?I.,Zor, U. and Lamprecht, S. Prostaglandins 2, 1.
9.
Saksena, S. K., Lau, I. and Shaikh, A. 25, 636.
(1973) Nature (&
Biology)
(1963) -Gen. and Camp. Endocr.
(1973) Nature (NaJ Biology)
(1973) -Adv. Bio-
(1972)
(1974) -Fert. Steril.
OCTOBER
10,1974 VOL. 8 NO. 1
PROSTAGLANDINS
10.
Sato, T., Taya, K., Fert. 39, 33.
11.
Behrman, H., Orczyk, G. P. and Greep, R. 1, 245.
12.
Kalra, S. P. and McCann, S.
Jyujo, T. and Igarashi, M.
(1973)
(1974) 2. Reprod.
(1972) Prostaglandins
Endocrinology 93, 356.
COMMENT Dr. Labhsetwar's discussion is most relevant to the interpretation of that portion of our data (1) indicating the failure of indomethacin treatment to appreciably reduce basal LH levels, which are obviously a reflection of both hypothalamic and pituitary activity. As for the question of the possible physiologic role of pituitary PGs in LRF-stimulated gonadotropin secretion and the relevance of our negative findings to it, we have now preliminary evidence to suggest that the POsynthetase of human pituitary has a lower sensitivity to the inhibitory action of non-steroid anti-inflammatory drugs as compared to other tissues. In a few experiments so far completed, the release of PGF -as measured by radioimmunoassay (2)- from fragments of human pitul*Z" ary tissue studied in vitro with the technique of continuous superfusion (3) is only slightly inhibited by the same concentration of drug capable of completely suppressing its release from the rat uterus and rabbit platelets (Patrono, Ciabattoni and Serra, unpublished experiments). Moreover, any interpretation of the effects of anti-inflammatory drugs should now take into account the recent observation of Mandel and Kuehl that indomethacin is a potent inhibitor of phosphodiesterase (4). If pituitary PGs do indeed mediate LRF-induced cyclic AMP formation and LH release, a combination of uncompletely depressed PG synthesis and of possibly inhibited phosphodiesterase activity is perhaps adequate to explain our negative results. In addition, this might account for the absence of dramatic endocrine changes in people undergoing chronic treatment with this family of drugs. C. Patrono, M.D. Dept. of Pharmacology Universitl Cattolica S. Cuore 00168 Rome, Italy
OCTOBER
10, 1974
VOL. 8 NO. 1
83
PROSTAGLANDINS
REFERENCES 1. Patrono, C. and Serra, G.B., Prostaglandins 6: 345, 1974. 2. Patrono, C. and Ciabattoni, G., in "Radioimmunoassay and Related Procedures in Medicine" vol. I: 451, International Atomic Energy Agency, Vienna, 1974. 3. Serra, G.B. and Midgley, A.R.Jr., Proc.Soc.Exp.Biol.Med. 133: 1370, 1970. 4. Kuehl, F.A.Jr., Prostaglandins 5: 325, 1974.
84
OCTOBER
10, 1974
VOL. 8 NO. 1