Biomedical subjects

G R Merriam

Publications and source records attributed to G R Merriam.

At least 37 records · Page 2Linked to original sources

PubMed1994

The antiprogestin RU486 delays the midcycle gonadotropin surge and ovulation in gonadotropin-releasing hormone-induced cycles.

OBJECTIVE: To investigate whether the antiprogestin RU486 acts primarily on the hypothalamus to delay the midcycle gonadotropin surge and thus gain insight into the site(s) of action of P in the control of ovulation. DESIGN: Prospective, crossover, single-blinded clinical study. SETTING: Outpatient clinic in an academic research environment. PATIENTS: Women with hypothalamic amenorrhea. INTERVENTIONS: RU486 or a placebo was given orally at a low dose of 1 mg/d for 5 days, starting when the dominant follicle reached 14 to 16 mm, to women with hypothalamic amenorrhea undergoing ovulation induction with GnRH pulses of unvarying frequency and dose. Blood samples and ovarian ultrasounds were obtained daily in the late follicular phase and every 3 to 4 days in the remainder of the cycle. MAIN OUTCOME MEASURES: Follicular diameter and plasma levels of LH, FSH, E2, and P. RESULTS: RU486 consistently delayed the timing of the midcycle gonadotropin surge and ovulation. Gonadotropin and steroid levels were suppressed during RU486 treatment, but follicular growth progressed normally in most patients. CONCLUSIONS: RU486 does not act primarily on the hypothalamus to delay ovulation. Rather, this compound appears to antagonize P at the pituitary level to suppress gonadotropin and steroid hormone secretion. P may thus act on the pituitary, independent of any hypothalamic effects, to regulate the timing of the midcycle gonadotropin surge and ovulation.

Adult↗

PubMed1994

Characterization of the normal progesterone and placental protein 14 responses to human chorionic gonadotropin stimulation in the luteal phase.

OBJECTIVE: To examine whether midluteal phase administration of the luteotrophic hormone hCG can result in higher and more stable serum levels than random sampling of P and placental protein 14 (PP14). DESIGN: Prospective controlled clinical study. SETTING: Normal human volunteers in an academic research environment. PARTICIPANTS: Twenty-six fertile, regularly cycling women. INTERVENTIONS: Blood samples were drawn at 0, 3, 6, 9, 12, 18, and 24 hours and then daily for the next 6 days, after a single IM injection of 5,000 IU hCG or saline given on day 5, 7, or 9 after the LH surge, as detected by rapid plasma assays. MAIN OUTCOME MEASURES: Serum P and PP14 measurements. RESULTS: Peak P and PP14 concentrations occurred at 6 hours and 5 days, respectively, after hCG stimulation on luteal phase day 9. Progesterone but not PP14 levels were significantly higher and less variable after hCG than after saline administration on this day. Progesterone responses exceeded 11.0 ng/mL (35.0 nmol/L) in all women, suggesting that this represents the cutoff limit for normal luteal function. Because PP14 responses were highly variable and inconsistent, it was not possible to determine a threshold for normal endometrial function. CONCLUSIONS: Midluteal phase administration of hCG in normal women induces consistent serum P levels > 11.0 ng/mL (35.0 nmol/L) but highly variable PP14 responses.

Adult↗

PubMed1993

Pituitary-testicular function in nephropathic cystinosis.

OBJECTIVE: To evaluate reproductive function in patients with cystinosis and in renal transplant recipients without cystinosis. DESIGN: Cross-sectional study. SETTING: Clinical Center, National Institutes of Health. PATIENTS: Ten male patients, 15 to 28 years old, with nephropathic cystinosis and renal allografts formed the study group; 11 renal transplant recipients who had a primary renal disorder other than cystinosis and were matched with study patients for age and renal function served as the control group. MEASUREMENTS: Tanner staging, serum gonadotropin determinations, and testosterone and testosterone-binding globulin assessments. Selected patients also had a human chorionic gonadotropin (HCG) stimulation test, a gonadotropin-releasing hormone (GnRH) stimulation test, and serial sampling for luteinizing hormone (LH). MAIN RESULTS: Although testosterone levels were within normal limits in 7 of 10 patients with cystinosis, the mean testosterone level in patients with cystinosis was 11.5 +/- 2.0 nmol/L compared with 24.2 +/- 3.0 nmol/L in control patients (P < 0.005). No patient with cystinosis reached Tanner stage 5 (full pubertal development), whereas 9 of 11 control patients did. Seven of 10 patients with cystinosis had elevations in LH or follicle-stimulating hormone (FSH) levels, suggesting testicular failure. These patients also had normal LH and FSH responses after GnRH stimulation, increased LH pulse frequency, and reduced testosterone response after HCG stimulation. In comparison, only 3 of 11 control patients had minimally elevated gonadotropin levels, and all 11 had normal testosterone levels. Microscopic testicular examination in one patient showed cystine crystals, germinal dysplasia, increased fibrosis, and Leydig cell hyperplasia. CONCLUSIONS: Abnormalities in the pituitary-testicular axis are common in male patients with cystinosis. These changes appear to be related to the disease cystinosis and not to treated renal failure per se.

Adolescent↗

PubMed1993

Sex hormones and headache.

A variety of evidence suggests a link between migraine and the female sex hormones. Women with migraine outnumber men by at least a 2:1 ratio and definite patterns of development and attacks are noted at menarche and throughout the period of menses, related to trimester of pregnancy, and again at menopause, although it may also regress. Hormonal replacement with estrogen can exacerbate migraine; oral contraceptives can change the character and frequency of migraine headache. This article will cover approaches to the therapy of hormone-related headaches associated with the menstrual cycle, menopause, and oral contraceptives.

Contraceptives, Oral↗

PubMed1993

Comparative analysis of progesterone and placental protein 14 measurements in the evaluation of luteal function.

OBJECTIVE: Our purpose was to investigate the diagnostic accuracy of single or summed measurements of progesterone and placental protein 14, a progestin-dependent endometrial glycoprotein, in the evaluation of luteal function. STUDY DESIGN: Forty-five healthy women had daily blood measurements of luteinizing hormone, progesterone, and placental protein 14 during one menstrual cycle. RESULTS: Thirty-nine women had normal and six had deficient luteal function on the basis of serial progesterone determinations. Luteal insufficiency was not accurately diagnosed by single progesterone or placental protein 14 values or by integrated placental protein 14 measurements. In contrast, the condition was correctly identified in all but one cycle when the sum of progesterone on days 4 and 7 was < 49 nmol/L (15.4 ng/ml). A poor correlation was found between peak or integrated measurements of progesterone and placental protein 14. CONCLUSION: Measurement of serum progesterone, but not placental protein 14, on 2 days of the midluteal phase provides a convenient and reliable test of luteal function.

Adult↗

PubMed1993

Induction of reversible growth retardation and growth hormone deficiency by blockade of norepinephrine synthesis in the rat.

Norepinephrine is a major regulator of the release of growth hormone. Diethyldithiocarbamate, a dopamine-beta-hydroxylase inhibitor, reduces norepinephrine synthesis and acutely inhibits growth hormone (GH) secretion. To investigate the long-term effects of dopamine-beta-hydroxylase blockade on growth, we administered diethyldithiocarbamate (0, 40, 100 or 400 mg/kg sc b.i.d.) to 21-day-old female rats for 10 days. Food intake, body weight, and tail length were measured twice a week. Plasma GH levels and hypothalamic dopamine and norepinephrine content were measured; messenger ribonucleic acids (mRNAs) for GH-releasing hormone and somatostatin were determined by quantitative in situ hybridization. Diethyldithiocarbamate administration decreased GH levels (p < 0.05) and retarded growth in a dose-dependent manner (p < 0.05), without altering food intake. Co-administration of GH partially reversed the growth retardation in diethyldithiocarbamate-treated animals (p < 0.05). Diethyldithiocarbamate treatment also increased the hypothalamic dopamine/norepinephrine ratio (1.13 vs 0.41 control, p < 0.05). Local levels of GH-releasing hormone and somatostatin mRNA were not altered by treatment. After discontinuation of diethyldithiocarbamate, growth rates returned to normal or transiently even to supranormal values. Norepinephrine synthesis blockade with diethyldithiocarbamate provides a model for reversible growth retardation, in which GH levels are decreased in the absence of decreased GH-releasing hormone mRNA. These results support a role for norepinephrine in the regulation of normal growth.

Animals↗

PubMed1993

Midluteal phase endometrial biopsy does not accurately predict luteal function.

OBJECTIVE: To investigate whether a midluteal phase endometrial biopsy accurately predicts luteal function. DESIGN: One nonpregnant menstrual cycle was evaluated in a prospective fashion. SETTING: Outpatient Clinic of the Clinical Center of the National Institutes of Health. PARTICIPANTS: Fifty healthy, normally cycling women. INTERVENTIONS: Serum progesterone (P) was measured daily throughout the luteal phase. An endometrial biopsy was performed 7 to 9 days after the luteinizing hormone (LH) surge, as detected by rapid plasma assays, and dated histologically according to Noyes' criteria. MAIN OUTCOME MEASURE: To correlate endometrial maturation with luteal P secretion. RESULTS: Mean integrated P measurements were reduced only when the lag between histologic and chronological dating was > or = 3 days or > or = 4 days, depending on whether chronological dates were assigned prospectively from the LH surge or retrospectively from the onset of next menses, respectively. However, these lags did not consistently predict deficient luteal function because subnormal integrated P secretion was seen in only 14% of women with these delays in endometrial maturation. CONCLUSIONS: Midluteal phase endometrial biopsy provides a crude test of luteal function that does not precisely distinguish luteal insufficiency.

Adult↗

PubMed1993

Accelerated heavy particles and the lens. VII: The cataractogenic potential of 450 MeV/amu iron ions.

PURPOSE: To determine the cataractogenic potential dose of high velocity iron ions as a fixation of dose administered singly or fractionated. The dose is critical to risk assessment and to theories of radiation action and cataractogenesis. METHODS: Twenty-eight-day-old rats were examined by slit-lamp biomicroscopy on a weekly-bi-weekly basis for more than 2 yr after radiation exposure. For the acute exposure study doses of 1, 2, 5, 25, and 50 cGy were evaluated. The fractionated regimens involved total doses of 2, 25, and 50 cGy. The reference radiation consisted of 50, 100, 200, or 700 cGy of 250 kilovolt (peak) x-rays. RESULTS: In accordance with previous findings in the rat using 570 MeV/amu 40Ar ions, the relative biologic effectiveness increased rapidly with decreasing dose, reaching values as high as 100. Unlike 40Ar ions, fractionation of the 56Fe doses did not produce a consistent enhancement at any of the doses examined. CONCLUSIONS: The data support the previous findings of a high cataractogenic potential for high linear energy transfer (LET) radiation. The effectiveness for the production of cataracts increases with decreasing dose relative to x-rays and is independent of dose protraction. Although the present study did not reveal a consistent enhancement of effect when the ions were applied in fractions, the results are consistent with at least one theory of the inverse dose-rate effect observed for high-LET radiation.

Animals↗

PubMed1993

Serum levels of placental protein 14 do not accurately reflect histologic maturation of the endometrium.

OBJECTIVE: To determine whether serum levels of placental protein 14, a major product of the progesterone-induced secretory endometrium, accurately reflect histologic maturation of the endometrium. METHODS: Daily serum levels of placental protein 14 were compared in 50 normally cycling women with normal or delayed endometrial maturation, as assessed by histologic dating of an endometrial biopsy in the midluteal phase of the same cycle. Ten of these subjects had placental protein 14 measurements but no biopsy in an additional cycle to examine the potential effects of the biopsy on secretion of this protein. RESULTS: Serum placental protein 14 concentrations started to increase 8 days after the LH surge and peaked at similar levels on the first day of the next menses in biopsy and non-biopsy cycles. The biopsy cycles had a shorter luteal phase but a slightly faster increase in placental protein 14 concentrations. Both the integrated secretion of this protein and single measurements on the day of the biopsy or at the onset of the next menses overlapped substantially in women with different degrees of endometrial development, even when differentiation of the endometrium was severely delayed. CONCLUSION: Serum measurements of placental protein 14 do not accurately predict, and thus should not replace, histologic evaluation of the endometrium at nidation.

Abortion, Habitual↗

PubMed1992

Gonadotropin suppression for the treatment of karyotypically normal spontaneous premature ovarian failure: a controlled trial.

OBJECTIVE: To determine if gonadotropin suppression improves ovarian follicle function or ovulation rates in patients with karyotypically normal spontaneous premature ovarian failure. DESIGN: Prospective, double-blind, placebo-controlled, crossover trial. SETTING: Tertiary care research institution. INTERVENTIONS: Two intervention phases lasting 4 months each: one placebo phase, and one treatment phase during which each patient received daily subcutaneous injections of 300 micrograms of the gonadotropin-releasing hormone agonist (GnRH-a) deslorelin. During both phases, patients took a standardized estrogen (E) replacement regimen. PATIENTS, PARTICIPANTS: Twenty-six patients with karyotypically normal spontaneous premature ovarian failure ranging in age from 18 to 39 years. MAIN OUTCOME MEASURES: We measured serum estradiol (E2) and progesterone (P) levels weekly during the 2 months after each intervention. We defined a serum E2 greater than 50 pg/mL (184 pmol/L) as evidence for ovarian follicle function and a serum P greater than 3.0 ng/mL (9.5 nmol/L) as evidence for ovulation. RESULTS: The GnRH-a therapy did not significantly enhance recovery of ovarian follicle function or the chance of ovulation. The power to detect a 40% and a 33% ovulation success rate with therapy was 0.95 and 0.83, respectively. We found evidence for ovarian follicle function in 11 of 23 women (48%), and 4 women (17%) ovulated. CONCLUSIONS: Patients with karyotypically normal spontaneous premature ovarian failure treated with E replacement did not benefit from the additional gonadotropin suppression achieved with GnRH-a. Because these patients have a significant possibility of spontaneous remission, attempts to induce ovulation should be limited to controlled trials designed to determine safety and effectiveness.

Adult↗

PubMed1992

Evidence for a critical role of progesterone in the regulation of the midcycle gonadotropin surge and ovulation.

Serum concentrations of progesterone begin to rise just before the midcycle gonadotropin surge that leads to ovulation. To examine the role of progesterone in the regulation of these events, we evaluated the effects of a low dose (1 mg/day, orally) of the antiprogesterone RU 486 on the timing of the gonadotropin surge and ovulation in normally cycling women. The drug or a placebo was given for 5 or 15 days, starting when the dominant follicle reached 14-16 mm. RU 486 consistently delayed the timing of the midcycle gonadotropin surge and the subsequent collapse of the dominant follicle, despite rising estradiol concentrations and normal follicular development. Unexpectedly, RU 486 also delayed the emergence of the periovulatory progesterone rise. The addition of progesterone (5-10 mg/day, im, for 2 days) to a 5-day course of RU 486 after the emergence of a mature follicle readily induced LH and FSH surges and completely reversed the effects of RU 486 at midcycle. Our results suggest that RU 486 delays the midcycle gonadotropin surge and ovulation by suppressing or antagonizing an ovarian progestational signal. Progesterone may, thus, represent the ultimate ovarian signal to the estrogen-primed hypothalamic-pituitary unit to trigger the gonadotropin surge that leads to ovulation.

Adult↗

PubMed1992

Photoperiod-driven changes in reproductive function in male rhesus monkeys.

Environmental lighting, which regulates seasonal breeding in many animal species, has not been examined as a regulator of reproduction or puberty in man or nonhuman primates. In this study we examined the effects of controlled alternating long and short daily photoperiods, independent of other environmental variables, on testicular size and function in rhesus monkeys. Sixteen animals, some pubertal, others prepubertal, were individually caged indoors in light-controlled rooms. They were subjected to a 32-week "year" with alternating 16-week cycles of long (16 h of light and 8 h of darkness) or short (8 h of light and 16 h of darkness) days. Animals were examined every 2 weeks over four 32-week "years". Body weight, testicular diameter, and testicular volume were measured, and blood was collected for testosterone and PRL determinations. We found that although short days did not trigger testicular development in prepubertal animals, testicular growth was markedly enhanced by short days in postpubertal animals, accompanied by increased plasma testosterone levels and reduced PRL levels. In long days, testes regressed, testosterone levels fell, and PRL levels rose. The periodicity of testicular size, as determined by spectral analysis, showed a strong signal at a cycle length of 31 +/- 13 weeks, but no signal at intervals close to the natural 52-week year, indicating that the observed periodicity is induced by the changes in lighting, rather than by circannual changes in other variables. These studies establish that changes in photo-period alone can modulate reproductive function in a higher primate and suggest that the onset of puberty is not directly driven by seasonal fluctuations in day length.

Animals↗

PubMed1991

Lack of effect of induced menses on symptoms in women with premenstrual syndrome.

BACKGROUND: No physiologic abnormality of the luteal phase has been consistently demonstrated in women with premenstrual syndrome (PMS). Using the progesterone antagonist mifepristone, we truncated the late luteal phase of the menstrual cycle in a blinded fashion to evaluate the relation of the events of the late luteal phase to the symptoms of PMS. METHODS: Fourteen women with PMS were given mifepristone (12.5 or 25 mg per kilogram of body weight) by mouth on the seventh day after the surge of luteinizing hormone. On the sixth through the eighth days after the surge, they also received injections of either placebo or human chorionic gonadotropin (2000 IU). Seven women with PMS received placebo instead of both mifepristone and human chorionic gonadotropin. All the women completed daily questionnaires measuring a variety of mood-related and somatic symptoms. RESULTS: Mifepristone consistently induced menses. The women receiving only mifepristone had plasma progesterone levels like those of the follicular phase (less than 3 nmol per liter) within four days, whereas all the other women had plasma progesterone levels characteristic of the luteal phase (greater than 8 nmol per liter) for at least seven days after treatment. In all three groups, the severity of symptoms was significantly higher after treatment than before, according to an analysis of variance with repeated measures. The level and pattern of the ratings of symptom severity were similar in all treatment groups. CONCLUSIONS: Neither the timing nor the severity of PMS symptoms was altered by mifepristone-induced menses or luteolysis. The temporal association of typical PMS symptoms with an artificially induced follicular phase suggests that endocrine events during the late luteal phase do not directly generate the symptoms of PMS.

Adult↗

PubMed1991

Increased peripheral T lymphocyte activation in patients with karyotypically normal spontaneous premature ovarian failure.

OBJECTIVE: To determine if soluble interleukin 2 (IL-2) receptor measured in serum by an enzyme-linked immunosorbent assay (ELISA) might be useful in managing patients with karyotypically normal spontaneous premature ovarian failure. DESIGN: Prospective, controlled observation. SETTING: Tertiary care research institution. INTERVENTIONS: None. PATIENTS, PARTICIPANTS: Twenty-four patients with karyotypically normal spontaneous premature ovarian failure comprised the study group. Forty-two healthy men and women comprised the normal reference group. MAIN OUTCOME MEASURES: We measured peripheral T lymphocyte human leukocyte antigen locus-DR (HLA-DR) expression and IL-2 receptor expression using monoclonal antibodies and flow cytometry. We measured soluble IL-2 receptor levels in serum using an ELISA. RESULTS: Consistent with previous findings, our patients had significantly higher HLA-DR expression on peripheral T lymphocytes (5.3 +/- 0.46) as compared with controls (3.5 +/- 0.34) (mean +/- SEM, P less than 0.01). Seven patients also had elevated IL-2 receptor expression on peripheral T lymphocytes (P less than 0.05). However, soluble IL-2 receptor levels in the serum did not differ significantly from normals. CONCLUSIONS: Patients with karyotypically normal spontaneous premature ovarian failure have a modest increase in peripheral T lymphocyte activation measured by flow cytometry. This degree of activation does not result in increased soluble IL-2 receptor release measured by ELISA.

Autoantibodies↗

PubMed1991

Evidence of genotoxic damage in human cataractous lenses.

Lens epithelial fragments (tags) recovered from individuals during routine cataract extraction have been assessed for cellular changes reflective of genotoxic damage. A high percentage of tags exhibited a population of micronucleated and polyploid cells. The presence and number of micronuclei (MN) in the epithelia of cataract patients appears to be independent of age and sex. However, a large number of MN in the epithelial cells of some individuals strongly suggests a history of compromised genomic integrity. While the study was not designed to define the role of DNA damage in the development of cataracts or to monitor human populations at risk of exposure to exogenous mutagens/cataractogens, the potential of the methodology to address each is demonstrated.

Adult↗

PubMed1991

Synchronization of hormonal time series: analytical approaches.

Comparison of the patterns of episodic secretion of two or more hormones measured simultaneously often suggests that peak levels tend to occur at around the same time. This visual impression can be misleading, however, as some peaks will occur simultaneously due to chance alone. Traditional cross-correlation methods are suitable for evaluating linkages among circadian and other smoothly varying rhythms, but are less well suited to correlating ultradian peaks. This paper proposes a method which entails identifying peaks of hormone secretion as discrete events in several different series, and counting the frequency of simultaneous and near-simultaneous peaks in temporal 'windows' of increasing width. The expected rates of random coincidences can be assessed by a variety of methods, including simulations and probability calculations. The method described utilizes simple techniques which make few assumptions about the character or stationarity of the series, comparing coincidence rates in the appropriately paired series with those in which a series in one subject is deliberately 'mismatched' with that of another subject. Using this approach, a significant excess of simultaneous peaks of luteinizing hormone (LH) and prolactin was found in normal subjects as compared with mismatched series (17% versus 6%; p less than 0.05). Hypogonadotrophic men treated with pulsatile gonadotrophin-releasing hormone (GnRH) have an even higher coincidence rate (26%). By contrast, the rate of coincidence between pulses of LH and cortisol is not significantly greater than that which would be expected due to chance.

Circadian Rhythm↗

PubMed1991

Changes in proopiomelanocortin messenger ribonucleic acid levels in the rostral periarcuate region of the female rat during the estrous cycle.

GnRH synthesis and release are regulated by a number of neurotransmitter systems. Several studies have implicated the opioidergic system as one of the important modulators of GnRH. To obtain an index of the activity of beta-endorphin-secreting neurons during the estrous cycle, we measured levels of proopiomelanocortin mRNA (POMC mRNA) in the periarcuate region at different cycle stages, using in situ hybridization. Ten female Sprague-Dawley rats (200-230 g) were killed at each of 11 times during the 4-day estrous cycle. Fresh frozen sections were made through the rostral arcuate nucleus and placed on gelatin-coated slides. A 48-base probe complementary to rat POMC mRNA was 3' end-labeled with [35S]dATP and applied to individual sections in hybridization buffer. Sections were washed and exposed to film. Relative amounts of POMC mRNA were measured by obtaining optical densities with an image analyzer. POMC mRNA levels varied significantly. At proestrus, they were low just before the onset of the LH surge, followed by a sharp rise that afternoon. On the day of estrus, POMC mRNA remained elevated and then declined again on metestrus. A second but smaller rise was seen in the late afternoon of metestrus. This pattern of changes in POMC mRNA is consistent with an inhibitory effect of beta-endorphin on GnRH after the midcycle surge and in the postovulatory phase of the cycle, while low levels of POMC mRNA in the early afternoon of proestrus may permit the release of GnRH, which triggers the LH surge. The changes in POMC mRNA approximately parallel changes in progesterone in the cycle.

Animals↗

PubMed1991

Growth hormone (GH) responses to the hexapeptide GH-releasing peptide and GH-releasing hormone (GHRH) in the cynomolgus macaque: evidence for non-GHRH-mediated responses.

GH-releasing peptide (GHRP; His-D-Trp-Ala-Trp-D-Phe-Lys-NH2), a hexapeptide derived from enkephalin, has been shown to have GH-releasing activity in man and several animal species. To characterize the GHRP dose-response curve and compare it with that of GH-releasing hormone [GHRH-(1-44)NH2], six unanesthetized young adult cynomolgus macaques were tested with a range of iv doses of GHRP or GHRH in random order. Animals were fitted with vests and tethers. Blood samples were obtained before and at 15-min intervals after the administration of drugs. Doses ranged from 0.03-3 mg/kg for GHRP and from 1-30 micrograms/kg for GHRH. The dose-response curves for the two peptides were not parallel. GHRP had lower potency, but evoked a much higher peak GH response than GHRH (greater than 55 vs. 12 micrograms/L). Because one of the proposed mechanisms of action of GHRP is the inhibition of somatostatin (SS), we tested the effects of propranolol, which inhibits SS, on the GH responses to GHRH and GHRP. Propranolol was given at a dose of 14 micrograms/kg, iv, 10 min before the injection of saline, GHRH (10 micrograms/kg), or GHRP (1 mg/kg). GH responses to propranolol alone did not differ from those to placebo (peak, 6 +/- 2 vs. 8 +/- 2 micrograms/L). However, propranolol pretreatment doubled the GH responses to both GHRH and GHRP compared with those to GHRH or GHRP alone 28 +/- 5 micrograms/L vs. 14 +/- 5 (P less than 0.05) and 54 +/- 2 vs. 25 +/- 6 micrograms/L (P less than 0.001), respectively]. These results show that GHRP causes a potent dose-dependent release of GH in this primate species. Since GHRP can produce a greater maximal GH response than GHRH, mechanisms other than release of endogenous GHRH must be involved.

Animals↗