Mechanism of induction of LH surge in the rhesus monkey: positive feedback of estrogen?

WEICK, RICHARD F., AND DAVID K. POMERANTZ. M~IMInisrn of ir&don of L,H surgc~ in thu r-hews rrm~&~.v: positiw f~dbrrr~k of estrqprz.2 Am. J. Physiol. 236( II: R102-R106, 1979 or Am. J. Physiol.: RegulatorG Integrative Comp. Physiol. 5( 1): R102-R106, 1979. Exper&nts were desiqed to determine whether the luteinizing hormone (LH) surge induced by estrogen results from a positive feedback effect of the steroid or from some alternative mechanism. Ovariectomiz& rhesus monkeys were implanted subcutaneously with different, numbers of Silastic capsules containing 17@estradiol, producing serum estrogen concentrations of 149 -+ 10, 245 2 13, or 452 -+ 26 pg/ml (mean 2 SE). All treatments caused an initial decrec?se in serum I,H levels followed by an LH surge. When serum estrogen was maintained at t,hese levels throughout the ensuing LH surge, peak LH levels varied, with signif’icantly lower LH peaks occurring in response to the lowest estrogen levels, a result suggestive of-either positive feedback or of 149 pg/ml being a marginally sufficient estrogen stimulus. When the estradiol implants were removed as the LH su~lge was starting, all animals showed LH surges of normal magnitude, apparently synchronized in time. This result suggests an interaction between the systems controlling the tonic and surge modes of LH secretion. They arc not broadly supportive of positive feedback as a critical mechanism controlling the LH surge. They rather suggest that estrogen is necessary to initiate the LH surge, but that its continued presence is not required to sustain that phenomenon.