The effect of various corticotropin-releasing factor trains on the release of adrenocorticotropin, beta-endorphin, and beta-lipotropin from perifused ovine pituitary cells

The dynamics of the release of proopiomelanocortin-derived hormones from ovine anterior pituitary cells in response to varying pulse characteristics of ovine corticotropin-releasing factor (CRF) were investigated with an in vitro automated 15-column simultaneous perifusion system. Columns of cells were stimulated continuously or with trains of CRF pulses of varying pulse length (2-16 min), pulse period (20-160 min), and concentration, for 500 min. Ovine ACTH, beta-lipotropin, and beta-endorphin immunoreactivity were measured by unextracted RIA. Each pulse of CRF stimulated clearly defined and highly correlated (r greater than 0.9) pulses of the three pituitary hormones, suggesting similar mechanisms controlling release. In dose-response experiments, the minimum concentration of CRF in a 10-min pulse required to significantly raise the output of ACTH was 200 pM, and initial responses had not attained maximal levels with concentrations of CRF increased to 2 microM. Responses to pulsed CRF stimulation decreased with time with all stimulation patterns selected, although previously unstimulated control columns retained the initial capacity to respond. Multiple linear regression analysis showed that hormone output per pulse of CRF (43 nM) increased with increasing pulse period and pulse length. Output of pituitary hormones per unit of CRF applied decreased with pulse length but increased with pulse period. In summary, the responses of proopiomelanocortin derivatives were shown to be sensitive to abrupt increases in CRF, to reduce output under continued stimulation, and to have an inherent time lag before responding maximally to subsequent pulsed stimulation.

Dynamic characteristics of luteinizing hormone release from perifused sheep anterior pituitary cells stimulated by combined pulsatile and continuous gonadotropin-releasing hormone

We aim to quantify and relate the dominant dynamic factors of GnRH signals and of the resultant patterns of LH release from pituitary cells. Using perifused sheep cells we have already shown that rising edges of GnRH pulses are major effectors of LH release and that a longer absence of signal between pulses improves response. This study reports the effects on LH release dynamics of continuous levels of GnRH with superimposed pulses and of slowing the important rising edge of the GnRH pulses. Low baseline GnRH perifusions at physiological levels (5-60 pM) reduced the response to hourly pulses of 850 pM GnRH. Continuous GnRH (420 pM), which initially yielded maximal LH release followed by desensitization, prevented extra stimulation by pulses of equal concentration, but 10-fold higher pulses gave additional LH output. After desensitization an hour's respite from stimulation resensitized cells to 420 pM pulses. Whereas continuous stimulation of cells with GnRH even at the very low level of 5-10 pM [ED50 = 58 +/- 6 (SE) pM] produced desensitization in 10-15 min, slowly rising GnRH (0.56-14 pM/min) caused increasing LH output with time. However, in comparison with square wave pulses, stimulatory signals consisting of slowly rising concentrations of GnRH produced peaks characterized by less total LH output and a changed shape. This was consistent with desensitization at low concentrations of GnRH reducing response to later increases in the level of stimulation. The mechanism for detecting GnRH signals and/or the mechanisms controlling release of LH were desensitized to constant GnRH at any concentration but retained a reduced sensitivity, or developed an additional release capacity, to increased levels of GnRH. Properties of four distinct types of LH release dynamics were described quantitatively and were shown to be controlled by different time constants in the GnRH pulse stimulation patterns.

The wheat mitochondrial gene for apocytochrome b: absence of a prokaryotic ribosome binding site

The wheat mitochondrial gene for apocytochrome b (CYB) has been identified by its hybridization to a yeast CYB probe and its nucleotide sequence has been determined. The wheat CYB sequence predicts a cytochrome b apoprotein of 398 amino acids; it is almost identical to that of maize but has ten additional amino acids at the carboxy terminus. No introns are present in the wheat CYB gene, but an internal segment of the gene is repeated at another genomic location. Transcript analysis reveals a single wheat CYB mRNA of approximately 2.4 kb with a long untranslated leader. Sequences upstream of the CYB coding region are very similar in wheat and maize but the stretch proposed to be a ribosome binding site in maize is not conserved in wheat. The corresponding leader regions of the wheat mitochondrial mRNAs for cytochrome oxidase subunits I and II also lack complementarity to the 3'-end of the small subunit rRNA. We conclude that alternative signals are involved in the initiation of translation in plant mitochondria.

Influence of the characteristics of pulses of gonadotrophin releasing hormone on the dynamics of luteinizing hormone release from perifused sheep pituitary cells

The effects were studied of varying the frequency, width and amplitude of pulses of gonadotrophin releasing hormone (GnRH) on the release of LH from anterior pituitary cells. Dispersed sheep cells supported in Sephadex were perifused with medium for 10 h and stimulated with different constant pulse patterns of GnRH. The timing of release of LH was measured by radioimmunoassay of the effluent fractions. Pulses of GnRH ranging in duration from 2 min every 8 min to 16 min every 128 min, and in concentration from 1.7 pmol/l to 250 nmol/l were applied to the cells, as well as continuous stimulation. Comparisons of differences between LH release patterns among samples of the same preparation of cells were used to demonstrate the effects of different GnRH stimulatory regimes. It was concluded that (1) the frequency of GnRH stimulation was important to the nature of LH release (periods shorter than about 16 min between pulses reduced LH output and caused faster desensitization of response), (2) the pulse width of GnRH input was important (the rising edge of the pulse produced greater LH output per unit of GnRH input than did continued application of GnRH within a pulse and wider pulses combined with shorter periods reduced LH output) and (3) over a threshold value of 5-10 nmol GnRH/l pulse amplitude had little further influence on LH output or rate of desensitization in dispersed cells. These findings reinforce the hypothesis that the rising edge of the GnRH pulse is the major stimulant to LH release.

Radioimmunological measurements of total LH in sheep pituitary cells

Procedures commonly used to extract LH from pituitary cells in order to measure total cell content were compared in four cell preparations. It was shown in 81 samples of cells suspended in 1 mM EDTA or 50 mM NaHCO3 that after freezing and thawing followed by any of a variety of treatments, there were no significant differences in the amounts of LH measured by RIA relative to the arbitrarily chosen reference treatment of vigorous pipetting. The additional treatments were multiple freezing and thawing, homogenisation, sonication, homogenisation in 25-100 mM Na2CO3 followed by rapid neutralisation, or none. The consistency of the results suggested that the same cellular pools of LH were being made accessible for measurement with all treatments. However, use of the more vigorous conditions of 1-2.5 M urea, 1% Triton X-100, or sonication on ice in 100 mM Na2CO3 decreased the amount of measurable hormone presumably due to its modification. In two cell preparations, homogenisation of cells in 100 mM Na2CO3 produced an additional 45% of measurable LH not accessible using other treatments nor from the source material in two other preparations.

Immunocytochemical localization of vitamin D-dependent calcium-binding protein in renal tubules of rabbit, rat, and chick

Vitamin D-dependent calcium-binding protein (CaBP) was localized in tissue sections of kidneys from rabbits, rats, and chicks using antiserum specific for chick intestinal CaBP. In rabbit kidney, CaBP was present in all cells of the distal convoluted tubule and most cells of the connecting tubule. Fewer, but still a majority, of the cells of cortical collecting ducts contained CaBP. The intensity of immunochemical staining and the number of stained cells decreased markedly in medullary collecting ducts, and only a few collecting duct cells contained CaBP at the junction of the inner and outer medulla. In the rat kidney, CaBP was present in all distal convoluted tubule cells, but the immunochemical staining was less intense than in the rabbit. The protein also was found in most connecting tubule cells of the rat; however, only a few collecting duct cells in the superficial corte of the rat contained CaBP. CaBP was essentially absent from mid- to deep-cortical collecting duct cells, while a very few collecting duct cells always contained CaBP at the junction of the inner and outer stripes of the outer medulla. In the chick, CaBP was present in distal convoluted tubule cells as the distal convoluted tubule coursed adjacent to the central vein. CaBP was absent from chick collecting duct cells. In all three species CaBP was not detected in the other portions of the nephron.

Urinary steroid metabolites and the overgrowth of lean and fat tissues in obese girls

Studies were made of steroid metabolites excreted in the urine of 17 obese girls 11.4 to 16.8 yr and 17 normal girls 11 to 17 yr. Creatinine excretion (muscle mass), total body water (or deuterium space), lean body mass and body fat were determined in the obese girls. Extracellular volume (corrected bromide space) was also measured and by difference with body water, intracellular water or soft tissue cell mass was calculated. In normal girls 24-h creatinine excretion was determined, but body water was predicted from height and weight. It was found, as in previous studies, that the obese girls had excess muscle mass and soft tissue cell mass for height. The excess growth of muscle, lean tissue, and body length in obese girls correlated with increments in oxosteroid (17 ketosteroid) excretion. The overall weight increase correlated with increased excretion of corticosteroid metabolites--a finding of interest since a physiological Cushing's syndrome was postulated for fat girls many years ago. When the normal and obese girls were divided by age at 14 yr and the subgroups compared (normal obese) the younger girls showed differences with respect to height, weight, total body water, fat and percentage fat. Differences in steroid metabolites were not found. In older girls the same findings were made again, but here it was clear that the increments in body size, particularly muscle mass, correlated with augmented oxosteroid excretion. Evidence is cited that these findings are not just related to a larger steroid pool in obese girls.

Pulpal reaction to bleaching of teeth in dogs

Hydrogen peroxide and heat are two components of a technique commonly used to bleach human teeth. The effects of these two components on pulp tissue of dog teeth were evaluated histologically. Hydrogen peroxide alone or with heat caused obliteration of odontoblasts, hemorrhage, resorption, and inflammatory infiltration, while heat alone was not detrimental. Pulpal changes demonstrated evidence of reversibility after 60 d.

Neonatal body water turnover: a putative index of perinatal morbidity

The water metabolism of 46 newborn babies was determined during a 10 day period by means of an isotope dilution technique, and correlations were sought with the clinical assessment of the babies by multiple obstetric and pediatric clinical criteria. The babies, 48 to 72 hours of age, were given a single oral dose (2 ml/kg) of deuterated water (D2O), a nonradioactive tracer, and the urinary excretion rate was followed by means of infrared spectrophotometry. After a period of equilibration of the D2O with body water (20 hours), the rate of D2O clearance was found to be a single exponential decay process, thus allowing the fraction of total body water lost each hour (the rate constant) to be calculated for each baby. The median values of the rate constants X 10(4)(h-1) for 14 growth-retarded babies ws 104 (98% confidence limits, 97.8 to 122) compared with 76.3 (67.0 to 80.2) for 16 normal mature babies and 82.1 (73.4 to 90.6) for 16 normal premature babies. These data indicate that, compared with normal mature or normal premature babies, growth-retarded infants have a significantly (P less than 0.05) faster turnover of water during the first 10 days of postnatal life. Since there was little overlap in results between the normally grown and the retarded infants, the measurement of water turnover may provide a useful index of perinatal morbidity.

Predicting the luteinizing hormone surge: relationship between the duration of the follicular and luteal phases and the length of the human menstrual cycle

Determination of blood serum levels of luteinizing hormone (LH) are used to detect the day of the midcycle surge. This information, collected over several menstrual cycles of numerous women, is used to derive mathematical expressions relating the day of the surge to the length of the cycle. The equations are subsequently employed to predict the most likely day of the LH surge, and hence the time of ovulation, solely from knowledge of the average length and variability of a woman's cycles, without the need for determinations of LH. A convenient table is provided for making this prediction.

Maturational changes in sheep ovarian follicles: gonadotrophic stimulation of cyclic AMP production by isolated theca and granulosa cells

Theca and granulosa tissues isolated from sheep ovarian follicles of different sizes were incubated in the presence of human chorionic gonadotrophin (HCG; 5 IU/ml) or follicle stimulating hormone (FSH; 5 microgram NIH-FSH-S11/ml) for 40 min. Changes in the total amounts of cyclic 3',5'-adenosine monophosphate (cAMP) were used as an index of the responsiveness of these preparations to the hormones. Thecal tissue of both large (4-6 mm in diameter) and small (1-3 mm) follicles responded similarly to gonadotrophins. Granulosa cells from small follicles failed to respond to stimulation by HCG. FSH, however, consistently increased cAMP production in comparison with controls or cells treated with HCG. Granulosa cells of large follicles responded to both HCG and FSH.

Perinatal mortality in South Australia

A study of the recorded causes of perinatal mortality has been made in South Australia for the years 1970 to 1973. The overall perinatal mortality was 22.16 per 1,000 births. Higher mortality was observed in babies of women resident outside the metropolitan area, of those aged under 20 and over 35 years, and of those not currently married. The most frequent causes of perinatal mortality were prematurity, placental insufficiency, congenital anomalies, maternal disorders and haemorrhage, in that order. Multiple pregnancy had a high perinatal mortality. Better recording systems with record linkage are required.

The work load and distribution of obstetricians and gynaecologists

A questionnaire to members of the College was returned, completed, by over half the members. It appears that very heavy work loads are carried by many members, and 44% of those in private practice consider themselves overworked. The opinion of 18% of the respondents is that too few specialists are being trained, and 61% of them said that too few general practitioner obstetricians are being trained. Eighty per cent believe that specialists and trained practitioners should practise obstetrics. Recertification is thought desirable by 79%, and continuing education by every respondent.

Cyclic AMP in sheep ovarian follicles: site of production and response to gonadotrophins

This study was undertaken (i) to establish a relationship between cyclic AMP (cAMP) production and the degree of LH and FSH stimulation; (ii) to determine the effects of various gonadotrophins on follicular formation of cAMP; and (iii) to identify the precise intrafollicular site of cAMP formation. The formation of cAMP increased rapidly in follicles exposed to LH. Maximum concentrations were reached after 90 min and were maintained for 180 min. Extracellular release of cAMP increased steadily throughout the 180-min experimental period. Tissue levels of cAMP increased proportionally and significantly when LH concentrations in the medium were increased from 0 to 200 mi.u. ml-1. Tissue levels of cAMP were significantly increased by HCG, prostaglandin E-2 and noradrenaline, but not by prolactin, prostaglandin F-2alpha, serotonin or melatonin. Cyclic AMP formation occurred predominantly in the thecal compartment; the membrana granulosa contributed less than 3% of the total amount of cAMP formed after gonadotrophic stimulation. A significant amount of cAMP from the thecal cells was released into the extracellular compartment and appeared to pass into the granulosa cells.

Pregnant mare serum gonadotrophin: rate of clearance from the circulation of sheep

The process involved in the disappearance of PMSG from the blood of sheep, following a single intravenous injection, has been separated into two exponential components. Values (mean plus or minus S.E.) calculated from experiments on five animals were: metabolic clearance rate (37.8 plus or minus 1.6 ml hr-minus 1); rate constant of disposal (0.0315 plus or minus 0.0016 hr-minus 1); half-time of disposal (21.2 plus or minus 1.1 hr). The stage of the oestrous cycle, ovariectomy and the dose of PMSG used had no apparent effect on these values.

Turnover of carnitine by rat tissues

Radioactive carnitine, in the form of L-[methyl-3H]carnitine, was administered intravenously to male rats and the specific radioactivity of carnitine in blood plasma and 13 tissues was measured for 16 days. There was no evidence of metabolism of carnitine to other compounds. A compartmental analysis was made by comparing the variation with time of the specific radioactivity of each tissue with one of two models. Kidney, heart and epididymal fat were best represented as containing a single compartment of carnitine, whereas spleen, liver, lung, adrenal, prostate, seminal vesicle, pancreas, muscle, testis and brain were best represented in terms of two compartments each exchanging carnitine with blood plasma. Estimates were obtained of the turnover times of carnitine in the individual tissue compartments as well as the fluxes across each compartment boundary. Analysis of the variation in the specific radioactivity of carnitine in urine and blood plasma. Estimates were obtained of the turnover times of carnitine in the individual tissue compartments as well as the fluxes across each compartment boundary. Analysis of the variation in the specific radioactivity of carnitine in urine and blood plasma indicated an average total excretion rate of carnitine of 10.4mumol/day, of which about 3.2mumol was found in the urine.

Calcium transport in the early conceptus and associated maternal tissues in the rabbit

1. The kinetics of calcium transport were studied in unmated (oestrous) and pregnant rabbits in the first half of gestation, with the aim of establishing evidence of hormonal (ovarian) influence on the pattern of transport. 2. The following tissues were examined at short- (45min and 2h) and long-duration (4, 16 and 48h) intervals after parenteral administration of (45)Ca or (47)Ca: maternal blood plasma, endometrium, uterine fluid, placental tissues, two developmentally disparate stages of rabbit conceptus, namely the unattached blastocyst and the early post-implantation foetus, and bone (femur). 3. Marked variability in calcium content characterized rabbit tissues and body fluids. 4. Compartmental analysis was applied to measurements of specific radioactivity. Oestrous endometrium had the largest rapidly exchanging calcium fraction (turnover time of 12min) and the highest value for calcium flux (500mug of Ca exchanged/h per g fresh wt. of tissue). A marked downward gradient in values of flux existed between the progestational endometrium, uterine fluid and blastocyst; there was a similar gradient between placental tissues and foetus. 5. An hormonal influence on calcium transport was evident in (i) the decrease in specific radioactivity of rabbit blood plasma with advancing pregnancy, (ii) the extraordinarily rapid calcium transport between blood plasma and endometrium, especially in the oestrous stage, and (iii) the effectiveness of ovarian hormone substitution in ovariectomized rabbits. 6. The very low specific radioactivity recorded for bone indicated that only a minute fraction of its calcium was exchanging with that of blood plasma under the experimental conditions examined. 7. The rate of uptake of (45)Ca by rabbit blastocysts growing in vitro was one-tenth of that of (22)Na, or that recorded for calcium in vivo. 8. Inhibition of carbonic anhydrase activity with acetazolamide in vivo, in maternal erythrocytes, endometrium and placental tissues, produced no appreciable changes in calcium uptake in these tissues or other systems examined as a routine on either day 6 or days 12-14 of gestation.

Effect of gonadotrophins on the production of steroids by sheep ovarian follicles cultured in vitro

The main objective of the study was to determine the rate at which Graafian follicles of sheep that had been treated with exogenous gonadotrophin acquire the ability to secrete oestrogen in vitro. Follicles were explanted from sheep 5 min to 24 h after injection of pregnant mare serum gonadotrophin (PMSG) and kept individually in culture for 7 days. The mean daily output of oestrogen by follicles from PMSG-treated sheep was higher than that secreted by follicles from untreated sheep. However, only a certain proportion of the follicles from each sheep secreted significant amounts of oestrogen in vitro; these follicles were called 'stimulated'. The proportion of stimulated follicles was 5% for control sheep, 20–30% for follicles explanted from sheep 5 min to 12 h after injection with PMSG, and 80% for follicles explanted from sheep that had been injected with PMSG 24 h previously.

In the second part of the study, the pattern of oestrogen and progesterone secretion by stimulated follicles of different sizes explanted from PMSG-treated sheep at various stages of the oestrous cycle was determined. Up to the 14th day, oestrogen production in vitro by follicles over 4·5 mm in diameter reached a maximum 2 days after PMSG injection and decreased thereafter; progesterone production rose steadily as the oestrogen levels declined. In contrast, follicles of less than 4·5 mm diameter secreted considerable amounts of oestrogen for the first 5 days in culture, but produced only small quantities of progesterone. In follicles explanted on day 15, oestrogen secretion decreased steadily from the beginning of the culture period and was very low by the 4th day. Most follicles explanted at oestrus secreted only small amounts of oestrogen in vitro but secreted large amounts of progesterone.