Sampling and Counting of Pulses

The frequency and amplitude of LH pulses provide a window to signals from the brain and pituitary gland. Withdrawal of blood at 5- or 10-min intervals for 12-24 h will capture the majority of discrete LH release episodes in healthy men (34,90-94). Suitable monitoring paradigms define an accelerated frequency and attenuated amplitude of pulsatile LH release in older men by independent methods of pulse detection, in separate gonadotropin assays, and in different volunteer cohorts (28,39,40,55,95). Figure 6A illustrates comparisons by age of immunoradiometic LH concentration times series collected every 10 min for 24 h, and Fig. 6B presents robotics-assisted chemilu-minometric LH release patterns monitored every 2.5 min over night (27,31). Simultaneous records of FSH, prolactin (PRL), and nocturnal penile tumescence are also shown. Some, but not all, earlier analyses using radioimmunoassay methods and/or less frequent (e.g., 20 min) blood-sampling protocols presaged the concept of lower amplitude and higher frequency LH peaks in older men (19,34-36). Recent biomathe-matical simulations establish that failure to detect either a loss of amplitude or a gain in

Prolactin Men

Fig. 6. (Continued) (B) LH concentrations monitored by sampling blood every 2.5 min overnight followed by chemiluminescence (robotics-assisted) assay and Gaussian secretory-burst deconvolution analysis (continuous curves [top row]). Simultaneous records of follicle-stimulating hormone (FSH) (upper middle), prolactin (PRL) (lower middle), and nocturnal penile tumescence (NPT) (bottom) are shown for comparison. (Adapted from ref. 32.)

Fig. 6. (Continued) (B) LH concentrations monitored by sampling blood every 2.5 min overnight followed by chemiluminescence (robotics-assisted) assay and Gaussian secretory-burst deconvolution analysis (continuous curves [top row]). Simultaneous records of follicle-stimulating hormone (FSH) (upper middle), prolactin (PRL) (lower middle), and nocturnal penile tumescence (NPT) (bottom) are shown for comparison. (Adapted from ref. 32.)

Penis Stimulation Pulses

Fig. 7. Undersampling of luteinizing hormone (LH) release censors detection of LH pulses (top) and inflates estimates of LH secretory-burst mass. The resultant technical bias limits the identification of age-related contrasts in pulse frequency and size. Twenty-four LH concentration time series were edited from original 10-min sampling sets to yield 30-min daughter series (simple subsets) in 11 young and 13 older men. (Unpublished reanalysis of data in 28,29,55; Bradford, Kuipers, and Veldhuis.)

Fig. 7. Undersampling of luteinizing hormone (LH) release censors detection of LH pulses (top) and inflates estimates of LH secretory-burst mass. The resultant technical bias limits the identification of age-related contrasts in pulse frequency and size. Twenty-four LH concentration time series were edited from original 10-min sampling sets to yield 30-min daughter series (simple subsets) in 11 young and 13 older men. (Unpublished reanalysis of data in 28,29,55; Bradford, Kuipers, and Veldhuis.)

frequency of LH pulses is a predictable technical artifact of insufficiently intensive blood sampling (see Fig. 7).

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