Abstract
Summary
LH concentration in serum of heifers averaged 0.5 ng/ml and increased to peaks of 1.9, 7.3 and 11.1 ng/ml after a single iv injection of 5, 20 or 80 μg GnRH, respectively. Similarly, LH concentration in serum from mature bulls averaged 1.1 ng/ml before GnRH and increased to peaks of 9.2, 19.3 and 39.1 ng/ml after 10, 40 and 160 μg GnRH, respectively. The interval from GnRH to the LH peak and magnitude of the peak were positively correlated. Exposure of pituitary explants, in constant superfusion, to 1 or 4 ng GnRH increased LH release from a pre-treatment base line of 0.25 ng/mg/min to 0.94 and 1.50 ng/mg/min after 20 min, respectively. LH release did not return to base line by 40 min after exposure to GnRH. A comparison of purified porcine and synthetic GnRH revealed parallel increases in media LH concentration with time after GnRH.
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