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Intensive Direct Cavernous Sinus Sampling Identifies High-Frequency, Nearly Random Patterns of FSH Secretion in Ovariectomized Ewes: Combined Appraisal by RIA and Bioassay

Prince Henry’s Institute of Medical Research (I.C.), Clayton, Victoria 3168, Australia; Wallaceville Animal Research Centre (L.M.), Upper Hutt, New Zealand; and Endocrine Division, Department of Internal Medicine, School of Medicine, University of Virginia (J.V.), Charlottesville, Virginia 22908

Address all correspondence and requests for reprints to: Prof. Iain J. Clarke, Prince Henry’s Institute of Medical Research, P.O. Box 5152, Clayton, Victoria 3168, Australia. E-mail: iain.clarke{at}med.monash.edu.au

Analyses of FSH secretion suggest pulsatile, nonpulsatile, or compositely pulsatile and nonpulsatile release modes. This may reflect the reduced signal-to-noise ratio inherent in FSH pulse estimation procedures and/or immunological-biological assay inconsistencies. To address these issues, we sampled cavernous sinus and jugular venous blood concomitantly from ovariectomized sheep at either 5-min or 1-min intervals. Samples from the former were assayed by RIA, and those from the latter by RIA and bioassay. Waveform-independent peak detection revealed FSH pulses occurring at high frequency. Pulsatile FSH secretion accounted for 28% of total secretion. Approximate entropy analysis showed that FSH secretion was nearly random. There was synchronous release of LH and FSH, but most FSH secretion was not associated with LH release; 13% of discrete FSH and LH pulses were concordant. We infer that FSH secretion exhibits pulsatile and basal/nonpulsatile features, with high-entropy features. Linear and nonlinear statistical measures revealed joint sample-by-sample synchrony of FSH and LH release, indicating pattern coordination despite sparse synchrony of pulses. We postulate that pattern synchrony of FSH and LH release is effected at the level of the gonadotrope. Concordant FSH and LH pulses probably result from pulsatile GnRH input, but other mechanisms could account for independent FSH pulses.