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Release of E Prostaglandins into the Cerebrospinal Fluid and Its Inhibition by Melatonin after Cervical Stimulation in the Rabbit^*

Department of Physiology and Pharmacology, University of Queensland, St. Lucia, 4067, Queensland, Australia

Address requests for reprints to: Prof. G. D. Thorburn, Department of Physiology, Monash University, Clayton, Victoria 3168, Australia.

Abstract

The release of the E type of prostaglandin (PGE) into the cerebrospinal fluid of mature female rabbits was studied using an indwelling catheter in the cisterna magna. The cervix of the rabbit was stimulated 5 min after the central injection of either vehicle or melatonin solution. PGE was measured by RIA, and in unstimulated animals, the level of PGE remained steady at about 4 ng/ml. After stimulation of the cervix of control rabbits, PGE levels rose by 31 ng/ml 40–70 min after the initiation of stimulation in those animals which subsequently ovulated. PGE levels rose by only 15 ng/ml 70–115 min after stimulation in those rabbits which did not ovulate. In the melatonin-treated rabbits, PGE levels remained close to those in unstimulated controls, and ovulation did not occur. Thus, stimulation of the cervix of the rabbit produces a rise in PGE levels in cerebrospinal fluid. This endogenous PGE surge may, in turn, cause the release of LHRH and LH and induce ovulation if levels exceed a critical threshold. A weaker stimulus leads to only a smaller surge of PGE, insufficient to cause ovulation. Melatonin blocked the stimulation-induced rise in cerebrospinal fluid PGE levels and ovulation, and appears to exert its antigonadotropic activity in the rabbit by the inhibition of central PGE synthesis.

Footnotes

^* This work was supported by the National Heart Foundation and the National Health and Medical Research Council of Australia.

Received June 4, 1981.

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