James R. Kerrigan

Variations of Pulsatile Growth Hormone Release in Healthy Short Prepubertal Boys

ABSTRACT: Overnight growth hormone (GH) concentrations obtained by frequent venous sampling of 20 healthy, short prepubertal boys were evaluated using the objective pulse detection algorithm, CLUSTER. The resulting pulsatile characteristics were compared with those of 11 healthy prepubertal boys of normal stature and with those of nine prepubertal children with documented GH deficiency. Although no significant differences of pulsatile GH release were found between the normal and short subjects, a subset of the short prepubertal boys with significantly delayed skeletal ages had subnormal sum of GH pulse areas and sum of GH pulse amplitudes. The finding of a significant correlation in all subjects between growth velocity and the sum of GH pulse amplitudes is important, as the results are compatible with the hypothesis that alterations of amplitude-modulated GH release underlie the pathophysiology of suboptimal growth in some short prepubertal children.

Androgen-receptor blockade enhances pulsatile luteinizing hormone production in late pubertal males : evidence for a hypothalamic site of physiologic androgen feedback action

ABSTRACT: To determine potential mechanisms by which androgens alter gonadotropin secretion and elimination in the pubertal male, we administered the potent nonsteroidal androgen receptor blocking agent, flutamide, to eight males with Tanner IV or V genital development. Venous blood samples were obtained every 10 min for 24 h and assayed for LH by a sensitive and high-precision fluorimmunoassay. Subjects were studied before and after the administration of flutamide. Deconvolution analysis was used to assess specific pulsatile LH secretory characteristics and estimate LH production and metabolic clearance rates quantitatively. After antagonism of endogenous androgen action, mean 24-h serum LH concentrations increased significantly. An increased mean 24-h LH production rate, without evident changes in serum LH half-life, accounted for the increase in average serum LH levels. The increased daily secretion rate of LH was in turn due to both an augmented mass of LH released per secretory episode and increased frequency of secretory events. There was no demonstrable change in the maximal rate of LH secretion attained within each secretory event. Serum concentrations of total testosterone, free-testosterone, and 17β-estradiol all increased during blockade of androgen action. Administration of the antiandrogen had no measurable effect on the pituitary response to a single maximally effective dose of exogenous gonadotropin releasing hormone (GnRH). These results indicate that, in the late pubertal male, endogenous androgen exerts negative feedback control of gonadotropin secretion primarily at a hypothalamic site reflected by regulation of the frequency of pulsatile LH secretion. Antiandrogen had no discernible effects on exogenous GnRH-stimulated pituitary LH release or on the elimination rate of LH, but amplified the mass of LH secreted in response to endogenous GnRH. Assuming that pituitary response to exogenous GnRH reflects responsivity to endogenous releasing factor, we can infer an augmentation of the endogenous GnRH stimulus when androgen negative feedback is withdrawn. Accordingly, we suggest that endogenous androgen acting via androgen receptors negatively regulates both the amount and frequency of hypothalamic GnRH release in late pubertal boys.

The accuracy and precision of an open-circuit system to measure oxygen consumption and carbon dioxide production in neonates.

ABSTRACT: We measured the oxygen consumption, carbon dioxide production, and respiratory quotient during the combustion of a known mass of anhydrous ethanol and methanol to assess the accuracy of an open-circuit flowthrough system. Continuous measurements were made of the mass of alcohol burned, the velocity of gas flow through the apparatus, and simultaneous measurements of the fractional concentration of oxygen, carbon dioxide and nitrogen of the inlet and outlet gas using paramagnetic oxygen analyzer, infrared carbon dioxide meter, and mass spectrometer. Standard respiratory and stoichiometric equations were used to calculate the oxygen consumption, carbon dioxide production and RQ for the mass of absolute alcohol combustion per unit time. In a series of 12 consecutive laboratory experiments (on 7 days), the measured values of gas exchange (similar to the rate of respiratory gas exchange by an infant of 1-4 kg) were in agreement within 5% of the true values for ethanol and methanol combustion, confirming the validity of the open-circuit method. The paramagnetic oxygen analyzer and the mass spectrometer gave similar oxygen consumption results and differed very little when the rate of absolute alcohol combustion was used to quantify the accuracy of the complete measurement system. A positive measurement error was observed for the carbon dioxide production results from both the IR meter and mass spectrometer, with the result that the respiratory quotient measurements were 3.4-4.7% higher than the true value. The mass spectrometer gave more precise oxygen consumption results, whereas smaller variance of carbon dioxide production measurements was observed using the infrared CO2 meter. The sources of error and methods to reduce the overall system error were considered. By using a rigorous set of calculations we showed that the rate of combustion of a known mass of absolute alcohol was a suitable laboratory method for validation of respiratory gas exchange measurements made in the neonate.

Altered growth hormone secretory dynamics in prepubertal males with constitutional delay of growth.

ABSTRACT: We have used the technique of deconvolution analysis to determine if abnormalities in growth hormone (GH) secretion or metabolic clearance underlie the observed alterations in circulating hormone concentrations in a group of seven prepubertal males with constitutional delay of growth (SHORT-DBA). The results were compared with data obtained from 13 healthy, short prepubertal males (SHORT) and 11 healthy prepubertal male subjects of normal stature (NORMAL). Although the mean 12-h overnight GH production rates were invariant among the groups (8.0 ± 1.0 versus 7.3 ± 0.7 versus 6.7 ± 1.2 μg/ L, NORMAL versus SHORT versus SHORT-DBA for all comparisons), different secretory mechanisms were operative. The secretory burst half-duration (time interval of the secretory event at half-maximal amplitude) of the SHORT-DBA subjects (26 ± 1 min) was greater (p = 0.02) than that of the SHORT group (20 ± 1 min); values for both the SHORT and SHORT-DBA subjects were indistinguishable from that of NORMAL controls (22 ± 2). Both the mass of GH released per secretory episode and the maximal rate of hormone secretion were less [p < 0.02 and p < 0.01, respectively] for the SHORT-DBA subjects [16 ± 2 μg/unit of body distribution volume (Lv) and 0.6 ± 0.1 μg/Lv/min, respectively] compared with those of the NORMAL (26 ± 2 μg/L, and 1.1 ± 0.1 nig/Lv/min, respectively) and SHORT (28 ± 4 μg/Lv and 1.3 ± 0.2 μg/Lv/min, respectively) groups; values for the latter two groups were indistinguishable. Given the dominant association of GH pulse amplitude with normal childhood growth, the present findings suggest a possible GH secretory mechanism underlying the suboptimal growth in a subset of prepubertal males with constitutional delayed growth.

Glucose-Stimulated Insulin Release by Individual Pancreatic β Cells: Potentiation by Glyburide

Abstract To investigate the effect of glyburide on insulin secretion by individual β cells from normal rats, we employed a reverse hemolytic plaque assay. Pancreata were harvested from female Wistar-Furth rats, the pancreatic islets isolated, and the latter dispersed into single cells. These cells were mixed with protein A-coated ox erythrocytes, the mixture was placed in a Cunningham chamber in the presence of insulin antiserum, and the cells were exposed to the various test substances. Having developed hemolytic plaques around the insulin-secreting cells with complement, the percentage of plaque-forming cells was determined and the plaque areas (reflecting the amount of insulin secreted) were quantitated. For the purpose of validation, we demonstrated that (i) plaque-forming (but not non-plaque-forming) cells could be identifed as insulin secreting by an independent immunofluorescent technique, (ii), plaques did not form if insulin antiserum was deleted from the preparation, (iii) plaques failed to develop if insulin antiserum was preabsorbed with insulin, and (iv) incubation with non-protein A-coated RBC or omission of complement resulted in no plaque formation. In addition, both the percentage of plaque-forming cells and the mean plaque area increased upon exposure to glucose (0.75–20 mM) in a concentration-dependent manner at 5- and 60-min incubation times. Moreover, somatostatin suppressed the percentage of plaque-forming cells and diminished the mean plaque area of cells which continued to secrete insulin in response to glucose. Exposure of cells to 100 nM glyburide in the presence of 5 mM or 20 mM glucose had no effect on the percentage of plaque-forming cells present at 5 min or 60 min. Similarly, glyburide did not alter mean plaque area at 5 or 60 min when cells were co-incubated with 5 mM glucose. However, mean plaque area was markedly enhanced at 5 and 60 min in response to glyburide and 20 mM glucose.

Exogenous androgen does not alter hypothalamic proopiomelanocortin gene transcript levels in the sexually immature male rat

To investigate possible mechanisms whereby the augmentation of hypothalamic proopiomelanocortin (POMC) messenger ribonucleic acid (mRNA) levels occurs with pubertal development, we employed the techniques of testosterone administration and in situ hybridization histochemistry in sexually immature male rats. Six animals from each of the following groups were studied: (1) untreated controls (CTRL); (2) empty capsule (SHAM); (3) testosterone capsule (TEST), and (4) untreated adults (ADLT). Capsules were implanted at 21 days of age. Groups 1-3 were sacrificed at 35 days of life; group 4 at 55 days. Ventral prostate and seminal vesicle weights were obtained to assess the biologic effect of testosterone. Hybridizations were performed on coronal brain slices through the region of the arcuate nucleus using a 35S-labeled oligonucleotide probe complementary to a 30-base sequence within POMC mRNA. Anatomically matched tissue sections (11 per animal, from the retrochiasmatic region rostrally to the premammillary nucleus caudally) were exposed to x-ray film, followed by densitometric analysis. The mean serum testosterone concentration of the TEST group was significantly greater than that of the ADLT animals; values for the CTRL and SHAM rats were undetectable. The accessory sex organ weights of the ADLT animals were greater than those of the TEST rats; both values were greater than those of the CTRL and SHAM groups which were indistinguishable. Increased levels of hypothalamic POMC mRNA were observed in the male rat after pubertal development.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex-Steroid Effects on Perifused Pituitary

Sex steroids are known to affect growth and growth hormone (GH) secretion throughout mammalian life. Early studies on the imprinting effects of testosterone (T) on growth and GH secretion in rats (1) showed that neonatal gonadectomy (GX) caused significant disruption of GH secretion in adult male rats. Treatment of neonatally GX male rats with T during neonatal and adult life restored a significant component of the GH pulsatile pattern. The presence of the ovary prevented the imprinting effect of T that would occur if female rats had otherwise undergone neonatal GX (2). These imprinting effects most likely involve the brain as the primary target.

QUANTITATION OF CORTISOL (F) PRODUCTION AND ELIMINATION RATES IN PREMATURE AND TERM NEONATES: EVIDENCE FOR PULSATILE SECRETION

Pulsatile secretion of cortisol has not been documented in the newborn infant. Using repeated blood sampling and deconvolution analysis, we investigated F secretory and elimination dynamics in a clinically stable group of 5 premature [gestational age (GA) 24-34 wk] and 5 term neonates. Blood samples were obtained through umbilical arterial cannulae at 15-min intervals for a 6-h period. All plasma F determinations were >55 nmol/L (2.0 μg/dL), and pulsatile F secretion was observed in all infants. On average, 4 ± 1 discrete F secretory episodes were detected during the study. No significant differences were noted between the 2 groups of subjects with regard to 6-h mean plasma F, plasma corticosteroid-binding globulin, F secretory burst frequency, mass of F secreted per burst, F production rate (FPR) or plasma F half-life. However, the premature infants had a significantly longer F secretory burst half-duration (p = 0.007) and a lower maximal F secretory rate (p = 0.018) than the term infants. The 2 most premature infants had significantly greater mean plasma F and FPR than the other 3 premature and all the term infants.Extrapolating to 24 h and correcting for distribution volume of F and for body surface area, we estimate FPR to be approximately 17-24 nmol/m2/24 h (6.6-8.8 mg/m2/24 h) for neonates of ≥34-wk GA. These values are consistent with estimates of FPR in older children and adults determined using either deconvolution analysis or stable isotope-dilution methods.

Salpingitis in a sexually inactive adolescent with congenital virilizing adrenal hyperplasia

Abstract We report a sexually inactive adolescent female with congenital virilizing adrenal hyperplasia (CVAH) and associated urogenital maldevelopment. At the age of 16 6/12 years, she developed signs and symptoms of an acute abdomen. At surgery, gross inflammation of both fallopian tubes and bilateral hydrosalpinges were observed. An anaerobic, gram-positive coccus was isolated. A subsequent sinogram demonstrated reflux of contrast agent from the urogenital sinus through the endocervical canal into the uterus. We postulate that the abnormal urogenital anatomy in our patient provided a mechanism whereby retrograde passage of vaginal bacteria resulted in salpingitis. Consideration should be given to performing a vaginoplasty early in patients with CVAH and small urogenital openings so that the morbid consequences of gynecologic infection can be prevented.