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R P McIntosh

Publications and source records attributed to R P McIntosh.

27 records · Page 2Linked to original sources
PubMed1985

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.

Animals↗
PubMed1985

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.

Adrenocorticotropic Hormone↗
PubMed1985

Amplitude of episodic release of LH as a measure of pituitary function analysed from the time-course of hormone levels in the blood: comparison of four menstrual cycles in an individual.

Pulse amplitude and frequency are often used to describe measurements of LH in blood. Such analyses are compatible with models of LH being released from the pituitary in episodes that are controlled by pulses of hypothalamic gonadotrophin-releasing hormone. The amplitudes of these secretory episodes as seen in blood are usually defined as the net heights of peaks above a baseline. As a measure of each pituitary secretory episode, this is valid only if peaks are regularly and widely spaced, making overlap negligible. When episodes are erratic and frequent so that only fractions of peaks have been cleared from the circulation before others follow, nadirs between peaks include output from previous episodes and do not define a physiologically meaningful baseline. Applied to overlapping peaks, such measures of amplitude usually underestimate pituitary secretory episodes and imply a tonic mode of LH secretion in addition to pulsatile release. Using the additional information of fitted LH clearance coefficients to define the shapes of LH peaks, a simple method based on an episodic mode of release alone is described, for estimating more accurately the relative sizes of secretory episodes as observed in blood, free of the effects of overlapping peaks. Using this analysis we have described the variation in amplitude, interval and clearance rates of LH secretory episodes within and between four normal menstrual cycles of a single individual. Thirteen, 3-6 h blood sampling sessions were performed during early follicular growth at the transition from luteal to follicular phases when the frequencies of LH peaks, LH/FSH ratios and progesterone concentrations were changing markedly.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1983

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.

Animals↗
PubMed1983

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.

Animals↗
PubMed1976

Fluorescence depolarization in a model system: carbonic anhydrase-dansyl sulphonamide.

The model system, carbonic anhydrase to which dansyl sulphonamide is specifically adsorbed, was chosen to test the fundamentals of the fluorescence depolarisation method. Fluorescence decay was shown to be satisfactorily represented by a single exponential decay term and the derived lifetime did not seem to vary significantly with mean excitation or emission wavelength. Depolarisation measurements were quite reproducible and those made with varying temperature were consistent with those performed with varying solution viscosity, thus excluding localised dye rotation. The calculated relaxation time, which was independent of wavelength of excitation or emission, was in conformity with a rigid spherical molecule of molecular weight 29 000 with 30% hydration.

Carbonic Anhydrases↗