1. Figure 1. Illustrative 24-h serum LH concentration (IRMA) profiles and calculated LH secretory rates as determined by deconvolution analysis in one healthy young man and one older man studied in fed and fasted states. Blood samples were collected at 10-min intervals for 27 h when volunteers were nutritionally replete (fed) and again during last 27 h of a 3.5-day fast. Fed and fasted sessions were assigned in randomized order at least 4 weeks apart. GnRH (10 μg iv) was administered after first 24 h of baseline sampling. Baseline is shown over time 0–1440 min (A and B), and post-GNRH responses over time 1440–1640 min (C and D). Continuous curves through observed serum LH concentrations (A and C) are predicted by deconvolution analysis (see Subjects and Methods). Vertical bars through sample LH concentration values denote dose-dependent intrasample sds (estimated from all 191 replicated samples in each original 27-h time series). Punctuated episodes of spontaneous LH release over 24 h or following GnRH iv (B and D) are computer-estimated LH secretory bursts (P < 0.05 vs. random sample variance), which give rise to pulsatile serum LH concentration profiles. Calculated mean number, duration, mass, and amplitude of LH secretory bursts and half-life of endogenous LH in eight young and eight older subjects each studied in both fed and fasted states are summarized in Table 2. Table 3 gives LH responses to iv GnRH (10μ g).
Fasting Suppresses Pulsatile Luteinizing Hormone (LH) Secretion and Enhances Orderliness of LH Release in Young but Not Older Men1
J Clin Endocrinol Metab. 1998;83(6): doi: /jcem
J Clin Endocrinol Metab | Copyright © 1998 by The Endocrine Society

2. Figure 2. Individual LH half-life (A) and LH secretory burst frequency (B) values in eight young and eight older men studied in fed vs. fasting state for 3.5 days. Blood was sampled at 10-min intervals for 24 h and assayed for LH content by IRMA. Deconvolution analysis was applied to quantitate various LH secretory measures (Table 2) and half-life. Numerical values are mean ± sem.
Fasting Suppresses Pulsatile Luteinizing Hormone (LH) Secretion and Enhances Orderliness of LH Release in Young but Not Older Men1
J Clin Endocrinol Metab. 1998;83(6): doi: /jcem
J Clin Endocrinol Metab | Copyright © 1998 by The Endocrine Society

3. Figure 3. Nyctohemeral (24-h) rhythmicity of deconvolution-calculated LH secretory burst mass (A) and LH interpulse intervals (B) for all subjects combined in each of two groups, specifically young (n = 8) vs. older (n = 8) men, as assessed by cosinor analysis of deconvolution measures (Subjects and Methods). NS, Not significant (P < 0.05) amplitude of 24-h periodic fit. Fitted amplitudes (and 95% statistically confidence intervals) are noted for significant group rhythms.
Fasting Suppresses Pulsatile Luteinizing Hormone (LH) Secretion and Enhances Orderliness of LH Release in Young but Not Older Men1
J Clin Endocrinol Metab. 1998;83(6): doi: /jcem
J Clin Endocrinol Metab | Copyright © 1998 by The Endocrine Society

4. Figure 4. Individual ApEn values of 24-h serum LH concentration profiles in fed vs. fasted young (n = 8) vs. older (n = 8) men. ApEn is a relative measure of disorderliness or irregularity of hormone release, with higher absolute values denoting greater irregularity. Conversely, lower ApEn values as observed in this study in young fasted men indicate more orderly patterns. Data are presented as indicated in legend of Fig. 2.
Fasting Suppresses Pulsatile Luteinizing Hormone (LH) Secretion and Enhances Orderliness of LH Release in Young but Not Older Men1
J Clin Endocrinol Metab. 1998;83(6): doi: /jcem
J Clin Endocrinol Metab | Copyright © 1998 by The Endocrine Society