Apparent Positive Cooperativity in the Mechanism of Action of Luteinizng Hormone
Dose response curves for cyclic AMP accumulation and testosterone prodduction were analyzed with respect to the apparent Km (ED50), apparent “Hill coefficient”, and basal and maximal production rates using a new computer program for a “four parameter” logistic function, employing weighted nonlinear least-squares regression. Results indicate the presence of apparent positive cooperativity for cyclic AMP production, with a Hill coefficient between 1.76 and 2.60, which is highly statistically significantly different from 1.0. For testosterone production, the calculated Hill coefficients were 1.44, 1.71 and 2.95. However, due to the large standard errors, these Hill coefficients were not significantly different from unity. These results are suggestive of the presence of positive cooperativity, or the presence of “quantal” mechanism at a level intermediate between binding and cyclic AMP production, or some other type of “threshhold” phenomenon. The methods employed should be generally useful for analysis of dose response curves from hormone-receptor binding systems.
KeywordsLuteinizing Hormone Leydig Cell Testosterone Production Positive Cooperativity Corticosterone Production
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- 2.Catt, K. J., and Dufau, M. L., Adv. Expt. Med. Biol. 36, 379, 1973.Google Scholar
- 3.Rodbard, D., and Hutt, D. M., Proc. Symposium on RIA and Related Procedures in Clin. Med. and Research, Int. Atomic Energy Agency, Vienna, Austria, in press.Google Scholar
- 4.Rodbard, D., Endocrinology, in press.Google Scholar
- 5.Mackie, D., and Schulster, D., Biochem. Biophys. Res. Comm. 53, 1973.Google Scholar
- 6.Rodbard, D., Adv. Expt. Med. Biol. 36, 342, 1973.Google Scholar