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  • Title: Simulation of the early phase of the proestrous follicle-stimulating hormone rise after infusion of luteinizing hormone-releasing hormone in phenobarbital-blocked rats.
    Author: Blake CA.
    Journal: Endocrinology; 1976 Feb; 98(2):461-7. PubMed ID: 765123.
    Abstract:
    Four-day cycling rats were kept in a room with the lights on from 0500-1900 h. Plasma FSH concentrations in blood withdrawn through atrial cannulas at hourly intervals from 1400-2000 h on proestrus were very similar to serum FSH concentrations in blood collected by decapitation. Additional cannulated rats were bled at 20 min intervals from 1400-1600, 1600-1800, or 1800-2000 h. In most rats, plasma FSH concentration rose gradually to approximately three times pre-rise levels by 1900 h. It then decreased slightly by 2000 h. Injection of an ovulation-blocking dosage of phenobarbital at 1345 h blocked the FSH rise. Rapid injection of 124 or 1240 ng of LHRH at 1300 h did not elevate plasma FSH by 1315 h but the 1240 ng dose did by 1400 h. Phenobarbital injection at 1230 h did not alter this response. In additional blocked rats, blood was rapidly withdrawen through one of two indwelling atrial cannulas while LHRH was infused at a constant rate through the other. Administration of LHRH by infusion was much more effective in elevating plasma FSH than was rapid injection of the releasing hormone. The pattern of plasma FSH concentration after infusion of about 50 ng of LHRH per hour from 1500-1810 h and then about 12 ng of LHRH per hour from 1810-1920 h was remarkably similar to that of the spontaneous FSH rise. These experiments imply that the early phase of the FSH surge (the one associated with the proestrous LH surge) is caused by a properly timed, nearly constant-rate release of LHRH for about 3 h (beginning about 1500 h of proestrus) followed by a period of diminished LHRH release.
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