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Pulsatile Release of Follicle-Stimulating Hormone in Ovariectomized Rats Is Inhibited by Porcine Follicular Fluid (Inhibin)^*

MICHAEL D. LUMPKIN, LOUIS V. DEPAOLO and ANDRES NEGRO-VILAR

Department of Physiology, University of Texas Health Science Center at Dallas Dallas, Texas 75235

Address requests for reprints to: Dr. Andres Negro-Vilar, Section on Reproductive Neuroendocrinology, LRDT, NIEHS, NIH, P.O. Box 12233, Research Triangle Park, North Carolina 27709.

Abstract

While the pulsatile release of LH in ovariectomized animals has been well established, little information exists concerning the pulsatile release of FSH and the factors involved in its regulation. The present studies analyzed the characteristics of episodic FSH secretion and examined the effects of ovarian feedback signals on that pattern. From conscious unrestrained ovariectomized rats, blood was collected at 10-min intervals for a period of 3 h. A pulsatile pattern of FSH was observed in the plasma of control rats, with an average frequency of 4 peaks/3 h, while LH oscillations occurred at an average of almost 6 peaks per 3 h. The injection of porcine follicular fluid (PFF; 0.5 ml), a source of inhibin, reduced FSH peak frequency to 2.5 peaks/3 h (P < 0.005). In the third hour of blood sampling, PFF also significantly lowered the average FSH peak amplitude (P < 0.05), the trough value, and the average mean value for that hour. In contrast, none of these parameters for LH was altered by PFF. Estradiol benzoate (EB; 20 µg, sc, 24 h before bleeding) significantly reduced LH peak frequency, mean trough value, and average mean value, whereas it only reduced the mean FSH average value and mean trough value. Combined treatment with EB and PFF synergized to decrease the mean value, trough value, peak frequency, and peak amplitude of episodic LH release.

Pituitary responsiveness to LHRH was evaluated after the treatments described above. PFF inhibited the response of FSH to LHRH, but not that of LH. EB by itself potentiated the release of both hormones. The combined EB/PFF treatment resulted in a decreased pituitary response in terms of FSH and LH compared to that of the EB-treated control group.

We conclude that the release of FSH occurs in a pulsatile fashion and, further, that this pattern of release is regulated by PFF (inhibin). It was also shown that an intriguing synergism between estradiol and inhibin exists to suppress LH release. (Endocrinology 114: 201, 1984)

Footnotes

^* This work was supported by NIH Grant 09908-06, Project III.

Postdoctoral Research Fellow supported by NIH Grant HD-07062.

Present address: Department of Physiology, University of Texas Health Science Center at San Antonio, 7033 Floyd Curl Drive, San Antonio, Texas 78284.

Received September 1, 1982.

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