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The effects of intravenous injection of synthetic luteinizing hormone releasing hormone (LH-RH) on the release of LH and FSH have been studied in the adult guinea-pig. In all the experiments the secretion of FSH was apparently unaffected by administration of LH-RH. The release of LH was log dose-dependent over the range 0·5–50 µg LH-RH.

During the female cycle, the maximum increment in the concentration of LH after a single i.v. injection of 0·5 µg LH-RH decreased progressively from day 1 to day 13. Double or triple injections of 1 µg LH-RH at 1 h intervals produced no potentiation on day 3 but progressively greater LH responses occurred on days 7, 10 or 13 of the oestrous cycle. Ovariectomy immediately before the first injection of LH-RH on day 7 blocked the potentiated response to subsequent injections, whereas ovariectomy immediately before the second injection still permitted this potentiation. These results suggest that there is direct ovarian involvement in the potentiated response to LH-RH observed during the later part of the guinea-pig oestrous cycle.

Infusion of LH-RH (1 µg over 200 min) produced a potentiated release of LH in female guinea-pigs on day 7 (but not on day 3) of the oestrous cycle after a delay of 1·5 h. It is proposed that there are two 'pools' of LH in the pituitary gland of the female guinea-pig and that the second pool is 'activated' consequent upon previous hypophysial stimulation of secretion from an ovary containing adequately developed follicles.

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				D. Grove-Strawser, S. A. Sower, P. M. Ronsheim, J. B. Connolly, C. G. Bourn, and B. S. Rubin Guinea Pig GnRH: Localization and Physiological Activity Reveal That It, Not Mammalian GnRH, Is the Major Neuroendocrine Form in Guinea Pigs Endocrinology, May 1, 2002; 143(5): 1602 - 1612. [Abstract] [Full Text] [PDF]