Paradox of the dose response to polypeptide hormones

Highest concentrations of follicle-stimulating hormone (FSH) are required to elicit maximal increases in cAMP formation by isolated Sertoli cells in culture, and progressively lower concentrations are required to increase three late responses maximally (estradiol synthesis from testosterone, DNA synthesis, and synthesis of androgen-binding protein, respectively). Identical dose-response curve relations are observed when cholera toxin is used as the stimulatory agent. Results do not rule out the possibility that cAMP could mediate the various responses of Sertoli cells to FSH.