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  • American Physiological Society  (18)
  • 1
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    Temporal structure of in vivo growth hormone secretory events in humans
    American Physiological Society ; 1991
    In:  American Journal of Physiology-Endocrinology and Metabolism Vol. 260, No. 1 ( 1991-01-01), p. E101-E110
    Details
    In: American Journal of Physiology-Endocrinology and Metabolism, American Physiological Society, Vol. 260, No. 1 ( 1991-01-01), p. E101-E110
    Abstract: The time course of spontaneous growth hormone (GH) secretion was studied in 12 normal men by analyzing serum GH concentrations measured in blood collected at 5-min intervals over 24 h with a multiple-parameter deconvolution model to simultaneously resolve endogenous GH secretory and clearance rates. Twenty-four-hour profiles of serum GH concentrations were accounted for by an average of 12 +/- 1.2 (SE) discrete GH secretory bursts having a mean half-duration (duration at half-maximal amplitude) of 25 +/- 2.3 min, indicating that 95% of daily GH secretion occurred in 8.8 h. The majority (96%) of GH was secreted in volleys composed of multiple (4.0 +/- 0.4) discrete secretory bursts. Such volleys of GH secretion were separated by 171 +/- 19 min, whereas their constituent individual secretory events occurred every 36 +/- 1.7 min (P = 0.0001). Between secretory volleys, calculated GH secretory rates fell asymptotically to zero. Significant positive and negative autocorrelations were observed for the series consisting of successive GH secretory burst mass and interburst intervals, respectively. Linear regression analysis revealed significant negative correlations between the mass of GH secreted per burst and both the preceding and following interburst intervals. Estimates of the half-life of endogenous GH (17 +/- 1.7 min) and of the endogenous GH production rate (0.25 +/- 0.033 mg/m2 for an assumed distribution volume of 7.9% body wt) agreed well with earlier independent measurements. We conclude that the human pituitary gland secretes GH in volleys consisting of multiple secretory bursts, without measurable intervening tonic secretion. This pattern of in vivo GH release in normal humans is consistent with a model of high-frequency GH-releasing hormone secretory events superimposed on low-frequency episodes of somatostatin withdrawal.
    Type of Medium: Online Resource
    ISSN: 0193-1849 , 1522-1555
    URL: Article
    DOI: 10.1152/ajpendo.1991.260.1.E101
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1991
    detail.hit.zdb_id: 1477331-4
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  • 2
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    Impact of intensive venous sampling on characterization of pulsatile GH release
    American Physiological Society ; 1987
    In:  American Journal of Physiology-Endocrinology and Metabolism Vol. 252, No. 4 ( 1987-04-01), p. E549-E556
    Details
    In: American Journal of Physiology-Endocrinology and Metabolism, American Physiological Society, Vol. 252, No. 4 ( 1987-04-01), p. E549-E556
    Abstract: The effect of sampling intensity on quantitative properties of pulsatile growth hormone (GH) release was tested using an objective, statistically based pulse detection algorithm (Cluster). Seven normal young men had blood withdrawn at 5-min intervals for 24 h. The number of GH peaks/24 h (mean +/- SE) detected in the 5-min series (5.93 +/- 0.66) was significantly greater than the number of peaks documented in the constituent 10-min (3.45 +/- 0.28), 15-min (2.79 +/- 0.31), 20-min (2.86 +/- 0.64), 30-min (2.5 +/- 0.36), 45-min (2.21 +/- 0.21), and 60-min (1.93 +/- 0.23) series. The increased number of peaks detected with 5-min sampling reflected high-frequency pulsatile GH release occurring within the major GH secretory episodes. Both the mean widths and areas associated with peaks identified in the 5-min series were smaller than those documented with less intensive sampling. Peak amplitude did not change with sampling intensity. These data suggest that the major secretory episodes of GH release in normal young men encompass high-frequency GH secretory activity. That these high-frequency GH secretory events have not previously been described probably reflects the relatively infrequent sampling paradigms (e.g., every 20-30 min) commonly used in the past.
    Type of Medium: Online Resource
    ISSN: 0193-1849 , 1522-1555
    URL: Article
    DOI: 10.1152/ajpendo.1987.252.4.E549
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1987
    detail.hit.zdb_id: 1477331-4
    SSG: 12
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  • 3
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    Validity of methods of body composition assessment in young and older men and women
    American Physiological Society ; 1999
    In:  Journal of Applied Physiology Vol. 86, No. 5 ( 1999-05-01), p. 1728-1738
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 86, No. 5 ( 1999-05-01), p. 1728-1738
    Abstract: We examined the validity of percent body fat (%Fat) estimation by two-compartment (2-Comp) hydrostatic weighing (Siri 2-Comp), 3-Comp dual-energy X-ray absorptiometry (DEXA 3-Comp), 3-Comp hydrostatic weighing corrected for the total body water (Siri 3-Comp), and anthropometric methods in young and older individuals ( n = 78). A 4-Comp model of body composition served as the criterion measure of %Fat (Heymsfield 4-Comp; S. B. Heymsfield, S. Lichtman, R. N. Baumgartner, J. Wang, Y. Kamen, A. Aliprantis, and R. N. Pierson Jr., Am. J. Clin. Nutr. 52: 52–58, 1990.). Comparison of the Siri 3-Comp with the Heymsfield 4-Comp model revealed mean differences of ≤0.4 %Fat, r values ≥ r = 0.997, total error values ≤ 0.85 %Fat, and 95% confidence intervals (Bland-Altman analysis) of ≤1.7 %Fat. Comparison of Siri 2-Comp, DEXA, and anthropometric models with the Heymsfield 4-Comp revealed that total error scores ranged from ±4.0 to ±10.7 %Fat, and 95% confidence intervals associated with the Bland-Altman analysis ranged from ±5.1 to ±15.0 %Fat. We conclude that the Siri 3-Comp model provides valid and accurate body composition data when compared with a 4-Comp criterion model. However, the individual variability associated with the Siri 2-Comp, DEXA 3-Comp, and anthropometric models may limit their use in research settings. The use of anthropometric estimation methods resulted in large mean differences and a considerable amount of interindividual variability. These data suggest that the use of these techniques should be viewed with caution.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/jappl.1999.86.5.1728
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1999
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
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  • 4
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    Human pancreatic GRF stimulates phosphatidylinositol labeling in cultured anterior pituitary cells
    American Physiological Society ; 1983
    In:  American Journal of Physiology-Endocrinology and Metabolism Vol. 245, No. 6 ( 1983-12-01), p. E587-E590
    Details
    In: American Journal of Physiology-Endocrinology and Metabolism, American Physiological Society, Vol. 245, No. 6 ( 1983-12-01), p. E587-E590
    Abstract: The effects of natural and synthetic human pancreatic growth hormone-releasing factor (hpGRF) on 32P incorporation into phospholipids were studied in cultured rat anterior pituitary cells. Natural hpGRF (1:30 dilution) significantly (P less than 0.01) stimulated phosphatidylinositol labeling at all times studied (15, 30, and 60 min). Synthetic hpGRF-(1–40)OH also significantly (P less than 0.05; P less than 0.01) increased 32P incorporation into phosphatidylinositol in a dose-related (1–30 nM) and time-dependent (5, 10, and 30 min) manner. In contrast, phosphatidylcholine and phosphatidylethanolamine labeling was not affected at any time studied. Somatostatin (30 nM) did not affect basal or hpGRF-stimulated phosphatidylinositol labeling but inhibited the hpGRF stimulation of cyclic AMP accumulation and growth hormone release. These results suggest that the phosphatidylinositol cycle may be involved in the mechanism of action of hpGRF in the anterior pituitary gland.
    Type of Medium: Online Resource
    ISSN: 0193-1849 , 1522-1555
    URL: Article
    DOI: 10.1152/ajpendo.1983.245.6.E587
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1983
    detail.hit.zdb_id: 1477331-4
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  • 5
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    Biological activity of a growth hormone-releasing factor secreted by a human tumor
    American Physiological Society ; 1983
    In:  American Journal of Physiology-Endocrinology and Metabolism Vol. 244, No. 4 ( 1983-04-01), p. E346-E353
    Details
    In: American Journal of Physiology-Endocrinology and Metabolism, American Physiological Society, Vol. 244, No. 4 ( 1983-04-01), p. E346-E353
    Abstract: A substance released by a pancreatic islet cell tumor induced signs and symptoms of acromegaly in a young woman. The culture medium in which the tumor was placed after resection was added to rat anterior pituitary cells and incubated in vitro. Both newly synthesized and total rat growth hormone (GH) release as well as cellular cyclic AMP accumulation were stimulated in a dose-dependent manner by the tumor medium. Coincubation with somatostatin blocked these effects. The increase of cyclic AMP preceded the enhanced GH release, indicating that cyclic AMP may be a second messenger for the tumor factor(s). Neither prolactin nor luteinizing hormone secretion was affected by the tumor medium. When measured by a perfused cell column apparatus, there was a rapid and dramatic release of GH by the dispersed rat pituitary cells during a 2.5-, 10-, and 40-min pulse of tumor medium; both the onset and termination of the GH response reached maximal or control values, respectively, within 5 min. Pretreatment of the tumor medium with pepsin markedly attenuated the tumor medium activity, indicating the peptide nature of the factor(s). Finally, ultrastructural analysis indicated that the somatotrophs were degranulated by the tumor medium, whereas there was no similar effect apparent on the mammotrophs. Whether this tumor polypeptide is identical to native hypothalamic GH-releasing hormone remains to be proved.
    Type of Medium: Online Resource
    ISSN: 0193-1849 , 1522-1555
    URL: Article
    DOI: 10.1152/ajpendo.1983.244.4.E346
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1983
    detail.hit.zdb_id: 1477331-4
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  • 6
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    Calcium channel agonist BAY k8644 enhances anterior pituitary secretion in rat and monkey
    American Physiological Society ; 1985
    In:  American Journal of Physiology-Endocrinology and Metabolism Vol. 249, No. 3 ( 1985-09-01), p. E326-E329
    Details
    In: American Journal of Physiology-Endocrinology and Metabolism, American Physiological Society, Vol. 249, No. 3 ( 1985-09-01), p. E326-E329
    Abstract: A calcium channel agonist BAY k8644 was applied to anterior pituitary (AP) cells in vitro. BAY k8644 (0.1-10 microM) stimulated prolactin and growth hormone (GH) release from monolayer AP cultures; the calcium channel antagonist D-600 (1-10 microM) completely blocked this effect. By utilizing a perifusion system, we observed an immediate and sustained amplification of prolactin (2.9-fold), growth hormone (2.3-fold), and luteinizing hormone (LH, 1.6-fold) release during the 1-h application of BAY k8644 (3 microM). A hypophysiotrophic peptide pulse 4 h after the BAY k8644 was removed confirmed that the cells remained responsive to their natural secretagogues. In another perifusion study 10-3,000 nM BAY k8644 produced a graded increase in prolactin release that was maintained over the 30-min exposure period. Finally, individual primate mammotrophs and somatotrophs showed a marked enlargement of hemolytic plaque area, an index of hormone release, 1 h after BAY k8644 (1 microM). We conclude that this synthetic dihydropyridine enhances the rate of prolactin, GH, and LH release from AP cells of two species. Because this is the first synthetic calcium channel agonist, structure-function studies characterizing calcium channel activation and exocytosis are now feasible.
    Type of Medium: Online Resource
    ISSN: 0193-1849 , 1522-1555
    URL: Article
    DOI: 10.1152/ajpendo.1985.249.3.E326
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1985
    detail.hit.zdb_id: 1477331-4
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  • 7
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    Sleep-promoting effects of growth hormone-releasing hormone in normal men
    American Physiological Society ; 1993
    In:  American Journal of Physiology-Endocrinology and Metabolism Vol. 264, No. 4 ( 1993-04-01), p. E594-E598
    Details
    In: American Journal of Physiology-Endocrinology and Metabolism, American Physiological Society, Vol. 264, No. 4 ( 1993-04-01), p. E594-E598
    Abstract: Growth hormone-releasing hormone (GHRH) promotes rapid-eye-movement (REM) and non-REM sleep in animals, but there is little direct evidence for a hypnogenic action of GHRH in humans. In the present study, the possible somnogenic effects of intravenous bolus injections of a dose of GHRH eliciting physiological elevations of GH secretion in healthy young men were investigated. GHRH (0.3 micrograms/kg body wt) was given in early sleep [i.e., 1st slow-wave (SW) period], late sleep (i.e., 3rd REM period), and early sleep after sleep deprivation until 0400 h (i.e., 1st SW period). In the absence of sleep deprivation, injection of GHRH in early sleep did not modify SW sleep but increased REM sleep. GHRH administration in the third REM period was followed by a marked decrease of wake and an almost 10-fold increase in SW sleep. When GHRH was administered during the first SW period after sleep deprivation until 0400 h, the duration of wake decreased. Thus GHRH has sleep-promoting effects in young adults, particularly when given at a time of decreased sleep propensity.
    Type of Medium: Online Resource
    ISSN: 0193-1849 , 1522-1555
    URL: Article
    DOI: 10.1152/ajpendo.1993.264.4.E594
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1993
    detail.hit.zdb_id: 1477331-4
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  • 8
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    Sex-related differences in GH secretion in rat using reverse hemolytic plaque assay
    American Physiological Society ; 1986
    In:  American Journal of Physiology-Endocrinology and Metabolism Vol. 250, No. 6 ( 1986-06-01), p. E650-E654
    Details
    In: American Journal of Physiology-Endocrinology and Metabolism, American Physiological Society, Vol. 250, No. 6 ( 1986-06-01), p. E650-E654
    Abstract: It is not known whether enhanced growth hormone (GH)-releasing factor (GRF)-stimulated GH release observed in the male reflects differences in somatotrope numbers and/or secretory response to GRF. We addressed this question by using the hemolytic plaque assay which allows quantification of hormone secretion by single pituitary cells. Time-course studies and GRF-GH concentration-response relationships (0.01, 0.1, 1, 10, 100, 1,000 nM GRF) in age-matched male and diestrous day 2 female rats were compared by quantitating the percent of GH plaque-forming cells, and measuring the plaque areas. The male pituitary contained a greater percent (P less than 0.05) of somatotropes (% of plaque-forming cells 45 +/- 2 vs. 27 +/- 4% in the female; mean +/- SE). GRF induced a greater concentration-dependent increase in plaque areas in the male. Maximal responses were attained at 10 nM GRF in both sexes. However, mean maximal plaque area was significantly greater (P less than 0.001) and the EC50 was significantly lower (P less than 0.05) in the male (0.25 +/- 0.09 vs. 1.78 +/- 0.64 nM in the female). The data suggest that the greater percent of somatotropes in the male and greater secretory capacity and sensitivity to GRF may contribute to sex-related differences in GH secretion in the rat.
    Type of Medium: Online Resource
    ISSN: 0193-1849 , 1522-1555
    URL: Article
    DOI: 10.1152/ajpendo.1986.250.6.E650
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1986
    detail.hit.zdb_id: 1477331-4
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  • 9
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    Differential effects of forskolin on LH and GH release
    American Physiological Society ; 1985
    In:  American Journal of Physiology-Endocrinology and Metabolism Vol. 249, No. 4 ( 1985-10-01), p. E392-E397
    Details
    In: American Journal of Physiology-Endocrinology and Metabolism, American Physiological Society, Vol. 249, No. 4 ( 1985-10-01), p. E392-E397
    Abstract: The effects of forskolin, an agent which increases intracellular levels of cAMP, on basal luteinizing hormone (LH) and growth hormone (GH) release and on gonadotropin-releasing hormone (GnRH)-stimulated LH release were documented. Continuously perifused dispersed anterior pituitary cells from female rats at random stages of the estrous cycle were used. Secretory rates of both LH and GH increased in a concentration-dependent manner in response to a 1-h challenge with 0.03, 0.1, 0.3, 1, or 3 microM forskolin. In response to 0.3 microM forskolin, maximum GH release was achieved within 15-20 min, after which secretion decreased. In contrast, LH release increased gradually, became maximal at 1.5-2 h, and remained constant until the forskolin was withdrawn. Cells exposed to 10 nM GnRH for 4 h exhibited a biphasic release of LH with the interphase nadir occurring at 30 min. The second phase of LH release was enhanced by simultaneous addition of forskolin with the GnRH. Whereas second phase release did not increase further, exposure of the cells to forskolin for 60 or 120 min before GnRH resulted in increased first-phase LH release. We suggest that, whereas our data are consistent with a role for cAMP in mediating the acute release of GH, cAMP may be involved in the process through which nonimmediately releasable LH becomes available for release.
    Type of Medium: Online Resource
    ISSN: 0193-1849 , 1522-1555
    URL: Article
    DOI: 10.1152/ajpendo.1985.249.4.E392
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1985
    detail.hit.zdb_id: 1477331-4
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  • 10
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    Performance of LH pulse-detection algorithms at rapid rates of venous sampling in humans
    American Physiological Society ; 1984
    In:  American Journal of Physiology-Endocrinology and Metabolism Vol. 247, No. 4 ( 1984-10-01), p. E554-E563
    Details
    In: American Journal of Physiology-Endocrinology and Metabolism, American Physiological Society, Vol. 247, No. 4 ( 1984-10-01), p. E554-E563
    Abstract: To assess the influence of the sampling rate on the quantitative characterization of pulsatile luteinizing hormone (LH) release, we withdrew blood at 4-min intervals for 8 h in five men and at 1-min intervals for 2 h in six other men. For comparative purposes, significant LH pulses were enumerated by three independent, computerized pulse-detection algorithms currently available. Our results indicate that, although the absolute number of LH pulses detected was influenced by the particular algorithm used and the estimate of intra-assay variance, all three analyses yielded increased pulse-frequency estimates at more intensive rates of venous sampling. Moreover, using a fourth, modified pulse-detection algorithm intended to maximize recognition of true-positive LH pulses while minimizing both false-positive and false-negative pulses, we observed that venous sampling at 4- and 1-min intervals exposed 4- and 12-fold more LH pulses, respectively, than could be discerned at conventional sampling rates. At rapid rates of venous sampling, the pattern of LH pulses comprised high-frequency, low-amplitude LH pulsations superimposed on lower-frequency LH peaks. This pattern suggests that the pituitary gland is responsive to high rates of intermittent neural stimulation. Moreover, these observed profiles are consistent with rapid initial rates of LH disappearance and/or distribution that we could demonstrate after intravenous bolus injections of purified LH in hypogonadotropic volunteers. In conclusion, we have compared results from three different pulse-detection algorithms at various rates of venous sampling and demonstrated a critical influence of sampling rate on apparent LH pulse frequency in humans.
    Type of Medium: Online Resource
    ISSN: 0193-1849 , 1522-1555
    URL: Article
    DOI: 10.1152/ajpendo.1984.247.4.E554
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1984
    detail.hit.zdb_id: 1477331-4
    SSG: 12
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