Regulation of gonadotropin subunit messenger ribonucleic acid expression by gonadotropin-releasing hormone pulse amplitude in vitro

The present study examined the effect of GnRH pulse amplitude on alpha, LH beta and FSH beta mRNAs using an in vitro perfusion model. Pituitaries from 30-day-old female rats were dissociated and the cells plated for 48 h to allow attachment to collagen-coated microcarrier beads. The beads were loaded into perifusion chambers, preperifused for 1 h, and then given GnRH pulses (17.5-175 pg/ml) every 30 min for 24 h. Perifusate LH was measured after 2 h and 22 h of perifusion and alpha LH and FSH beta messenger RNAs (mRNAs) were determined by hybridization to complementary DNA (cDNA) probes. All doses of GnRH acutely stimulated LH release, and responses were similar after 2 h and 22 h. LH release increased as a function of GnRH pulse dose with maximal increases seen following 70 pg/ml pulses. alpha mRNA levels (control = 0.73 +/- 0.1 fmol cDNA bound/100 micrograms pituitary DNA) were increased 30% and 40% after 24 h of 35 and 70 pg/ml pulses, respectively (P < 0.05 vs. media controls). LH beta mRNA concentrations (control = 0.44 +/- 0.08 fmol cDNA bound) were only elevated after 35 pg/ml GnRH pulses (36% increase). FSH beta mRNA showed the largest responses to GnRH pulses, increasing by 45% and 84% after 35 and 70 pg pulses, respectively (control = 0.14 +/- 0.02 fmol bound). The highest GnRH pulse dose (175 pg/ml) was ineffective in stimulating an increase in FSH beta mRNA levels. These results show that all three gonadotropin subunit mRNA concentrations increase after 24 h of GnRH pulses, but the pattern of individual subunit mRNA responses was dependent upon the amplitude of the GnRH pulse stimulus. These data support earlier results in vivo, in that the subunit responses to GnRH pulse dose were similar. Thus, alterations in the amplitude of pulsatile GnRH secretion from the median eminence may be one mechanism by which the expression of gonadotropin subunit genes are regulated.

L-mandelate dehydrogenase from Rhodotorula graminis: comparisons with the L-lactate dehydrogenase (flavocytochrome b2) from Saccharomyces cerevisiae

L-Lactate dehydrogenase (L-LDH) from Saccharomyces cerevisiae and L-mandelate dehydrogenase (L-MDH) from Rhodotorula graminis are both flavocytochromes b2. The kinetic properties of these enzymes have been compared using steady-state kinetic methods. The most striking difference between the two enzymes is found by comparing their substrate specificities. L-LDH and L-MDH have mutually exclusive primary substrates, i.e. the substrate for one enzyme is a potent competitive inhibitor for the other. Molecular-modelling studies on the known three-dimensional structure of S. cerevisiae L-LDH suggest that this enzyme is unable to catalyse the oxidation of L-mandelate because productive binding is impeded by steric interference, particularly between the side chain of Leu-230 and the phenyl ring of mandelate. Another major difference between L-LDH and L-MDH lies in the rate-determining step. For S. cerevisiae L-LDH, the major rate-determining step is proton abstraction at C-2 of lactate, as previously shown by the 2H kinetic-isotope effect. However, in R. graminis L-MDH the kinetic-isotope effect seen with DL-[2-2H]mandelate is only 1.1 +/- 0.1, clearly showing that proton abstraction at C-2 of mandelate is not rate-limiting. The fact that the rate-determining step is different indicates that the transition states in each of these enzymes must also be different.

Transcutaneous bilirubinometry: clinical application

Simultaneous estimations of serum and transcutaneous bilirubin were done in 105 healthy, full term, jaundiced newborns. A good correlation was found between the transcutaneous and serum bilirubin values with coefficient of correlation 0.774. The observed sensitivity was 90%, specificity 78% and positive predictive value 64% at mean serum bilirubin concentration of 9.92 mg/dl. Two action levels at transcutaneous bilirubin values 15 and 18 were also generated that correlated with low and high serum bilirubin values; they can therefore be used for screening of jaundiced full term babies. This study indicates that the transcutaneous bilirubin meter is useful for screening of jaundiced neonates.

Enhanced effectiveness of pulsatile 3',5'-cyclic adenosine monophosphate in stimulating prolactin and alpha-subunit gene expression

cAMP is involved in the regulation of secretory activity in lactotrope, thyrotrope, and gonadotrope cells. The present study examined whether pulsatile or intermittent changes in cAMP are more effective than a continuous stimulation in increasing pituitary hormone gene expression. Pituitaries from adult female rats were dissociated, plated for 48 h (7-8 x 10(6) cells per well) to allow attachment to Matrigel-coated plastic coverslips, then inserted into perifusion chambers (five to eight chambers per group). After 24 h of treatment, the cells were recovered, RNA extracted, and messenger RNAs (mRNAs) determined by dot blot hybridization. Perfused cells were exposed to either hourly pulses of monobutyryl cAMP (Bt cAMP, 0.01, 0.1, or 1 mM; 1 mM butyrate pulses to controls), or continuously to forskolin (10 microM). Bt cAMP pulses increased both PRL and alpha-subunit mRNAs, maximal after the 0.1 mM dose for PRL (51% increase vs. butyrate controls) and after the 1 mM dose for alpha (60% increase). However, forskolin was ineffective in increasing PRL or alpha mRNA concentrations. TSH, LH, and FSH beta-subunit mRNAs were not altered by Bt cAMP pulses or forskolin. To confirm the different effects of pulsatile vs. continuous cAMP on PRL and alpha-subunit mRNAs, the response to pulsatile 8-bromo cAMP (1 mM) or Bt cAMP (0.5 mM) was compared to continuous Bt cAMP (0.5 mM). PRL and alpha-subunit mRNAs were increased by both cAMP analogs given in a pulsatile manner but not by continuous Bt cAMP. PRL and LH secretory responses (determined in perifusate samples after 2 h and 22 h of treatment) revealed that both PRL and LH release was increased by cAMP stimulation, given either in a pulsatile or continuous manner. These results show that PRL and alpha-subunit gene expression were sensitive to changes in cAMP stimulation, whereas that of TSH, LH, and FSH beta were unaltered. Only intermittent cAMP stimuli were effective in increasing PRL and alpha mRNAs. These data suggest that pulsatile fluctuations in intracellular cAMP may be essential for maximal expression of the PRL and alpha genes. Thus, intermittent changes in intracellular second messengers may be a necessary part of the pathway involved in the transduction of signals from the plasma membrane to the nucleus.

Differential actions of thyrotropin (TSH)-releasing hormone pulses in the expression of prolactin and TSH subunit messenger ribonucleic acid in rat pituitary cells in vitro

The influence of TRH pulse pattern on PRL and TSH alpha- and beta-subunit gene expression was examined in vitro. Pituitaries from adult female rats were dissociated and plated for 48 h to allow attachment to collagen-coated microcarrier beads. The beads were perifused for 24 h with TRH (pulses or continuous). To examine the effects of TRH pulse amplitude, TRH pulses (0.032-100 nM) were given every 60 min (controls received either medium pulses or continuous 100 nM TRH). PRL mRNA rose progressively to a peak at 4 nM TRH/pulse (93% increase vs. medium-pulsed controls), but higher TRH pulse amplitudes were less effective. alpha-Subunit mRNA also rose with increasing TRH pulse dose, with maximal (137%) elevations after 100-nM pulses. TSH beta mRNA concentrations were increased by TRH pulse doses between 0.8-20 nM, but a clear dose-response pattern was not seen. Continuous TRH (100 nM) resulted in PRL, TSH beta, and alpha mRNAs that were less than the values in medium-pulsed controls. To assess the effects of pulse frequency, 4-nM TRH pulses were given at intervals between 15-240 min (controls received medium pulses or continuous 4 nM TRH). PRL mRNA was increased (55-107% increase) after all pulse intervals, except 240 min, and rose to a similar degree after 4 nM TRH given continuously. alpha-Subunit mRNA concentrations increased by a lesser degree and also did not rise after the slowest (240 min) pulse interval. In contrast, TSH beta mRNA levels increased progressively as pulse intervals were increased, and maximal (85%) elevations were seen after 240-min pulses. Continuous 4 nM TRH did not alter alpha or TSH beta mRNAs. These results show that pulsatile TRH is more effective than continuous TRH in stimulating PRL, TSH beta, and alpha mRNAs. Further, the pattern of TRH pulsatile signals can influence the expression of these pituitary hormone genes in a differential manner.

Gonadal steroids effect similar regulation of gonadotrophin subunit mRNA expression in both male and female rats

Gonadal steroids can act both indirectly via gonadotrophin-releasing hormone (GnRH) and directly on the pituitary to regulate gonadotrophin subunit gene expression. Recent studies to assess a possible direct action at the pituitary have shown that testosterone, when given to males in the absence of endogenous GnRH action, selectively increases FSH-beta mRNA concentrations. Conversely, in females, oestradiol appears to regulate gonadotrophin subunit mRNAs primarily via GnRH. The present study was designed to determine whether these differing results reflect specific actions of the gonadal steroids themselves or different responses of the pituitary gonadotroph cells in males and females. Rats which had been castrated 7 days earlier were given silicone elastomer implants (s.c.) containing oestradiol (plasma oestradiol 68 +/- 4 ng/l) in males or testosterone (plasma testosterone 3.5 +/- 0.3 micrograms/l) in females in the absence or presence of a GnRH antagonist. Seven days later pituitaries were removed and steady-state mRNA concentrations measured by dot-blot hybridization. In males, oestradiol reduced LH-beta and FSH-beta but not alpha mRNA. The antagonist reduced levels of all three subunit mRNAs in males and the addition of oestradiol had no further effect, suggesting that oestradiol regulates gonadotrophin subunit gene expression in males by suppressing GnRH secretion. In females, testosterone reduced all three subunit mRNAs though FSH-beta remained threefold higher than in intact animals. The GnRH antagonist was as effective as testosterone alone and reduced alpha and LH-beta to levels found in intact animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Polymers for biodegradable medical devices. VIII. Hydroxybutyrate-hydroxyvalerate copolymers: physical and degradative properties of blends with polycaprolactone

The physical and degradative properties of polyhydroxybutyrate-hydroxyvalerate copolymer blends with polycaprolactone were investigated. Blends containing low levels of polycaprolactone (less than 20%) were found to possess a considerable degree of compatibility, whilst those with higher levels of polycaprolactone were incompatible and showed phase separation behaviour. This incompatibility was most marked in blends containing approximately 50% of each component. In blends containing low levels of polycaprolactone, processing conditions governed the ease of crystallization of polycaprolactone in the polyhydroxybutyrate-hydroxyvalerate matrix and thus the mechanical property of the blend. The degradation rate of these blends was found to be influenced by a complex set of factors, including temperature, pH and polycaprolactone content of the blend. Although crystallinity affected the mechanical properties of the blends, its influence on the hydrolytic degradation rate was masked by the large difference in the molecular weight of the polyhydroxybutyrate-hydroxyvalerate copolymers (MW approximately 300,000) and polycaprolactone. (MW approximately 50,000). The polyhydroxybutyrate-hydroxyvalerate/polycaprolactone blends were found to be much more stable to hydrolytic degradation than polyhydroxybutyrate-hydroxyvalerate/polysaccharide blends previously studied. Here the combined techniques of goniophotometry and surface energy measurements proved extremely valuable in monitoring the early stages of degradation, during which surface, rather than bulk degradation, processes predominate.

Polymers for biodegradable medical devices. V. Hydroxybutyrate-hydroxyvalerate copolymers: effects of polymer processing on hydrolytic degradation

The effects of melt processing on those properties of polyhydroxybutyrate-hydroxyvalerate copolymers that control hydrolytic stability were studied. Initial experiments using a non-thermal preparation technique enabled the relationship between initial molecular weight and rate of hydrolytic degradation to be established. This rate was conveniently expressed in terms of the time for 10% by weight of the sample to be eroded. By varying melt processing conditions, the range of effects of processing on sample molecular weight and molecular weight distribution were investigated. These effects were found to be quite dramatic, with a reduction to 50% of the initial molecular weight being readily achieved. Temperature, shear rate and dwell time interrelated to control the extent of thermal degradation achieved during processing. The principal effect of copolymer composition resulted from the fact that an increase in hydroxyvalerate content led to a reduction in melting point and enabled milder processing conditions to be used. Enhanced crystallinity, resulting from more favourable processing conditions reduced hydrolytic degradation rates. As a result, melt processing produced a complex interrelation of effects, all of which influenced the hydrolytic stability of the fabricated specimen. In general, molecular weight effects predominated.

Polymers for biodegradable medical devices. VII. Hydroxybutyrate-hydroxyvalerate copolymers: degradation of copolymers and their blends with polysaccharides under in vitro physiological conditions

The hydrolytic degradation of hydroxybutyrate-hydroxyvalerate copolymers was monitored in vitro at 37 degrees C and pH 7.4. Direct use of bulk properties such as weight loss and tensile strength did not reveal substantial changes in the polymer matrix over degradation periods of several months. Despite this, the polymers were demonstrated to undergo significant modification during this period, in ways that markedly influence their subsequent behaviour. Combined use of goniophotometry and surface energy measurements revealed that surface modification begins at an early stage and is accompanied by diffusion of water into the matrix and a progressive increase in polymer porosity. Relatively little change in the molecular weight and some increase in the crystallinity of the matrix occurred during these early months. As a result, the tensile strength of the polymer varies little in this period. As the porosity of the matrix increases, hydrolytic chain scission within the matrix and diffusion out of degradation products proceeds more effectively. Decrease in matrix molecular weight, increase in matrix erosion, weight loss and loss of tensile strength began at a much more dramatic rate. The apparent resistance of the polymer to degradation in the early months is followed by an accelerated degradation phase around and beyond 1 yr. The use of filters that can dissolve or hydrolytically degrade more rapidly than the hydroxybutyrate matrix accelerates the development of porosity within the matrix and thus enhances the decomposition process.

Polymers for biodegradable medical devices. VI. Hydroxybutyrate-hydroxyvalerate copolymers: accelerated degradation of blends with polysaccharides

The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in the form of blends with the polysaccharides amylose, dextran, dextrin and sodium alginate, has been studied under a range of conditions (pH 2.3, 7.4 and 10.6 and at 37 degrees C and 70 degrees C). The hydrolytic degradation of the PHB-PHV copolymers was found to be dramatically affected by the presence of polysaccharides. Its progress was characterized by an initial increase in the wet weight, with concurrent decrease in the dry weight as the polysaccharides eroded from the matrix. Surface energy measurements and goniophotometry proved to be particularly useful in monitoring this stage of the degradation process. The concurrent increase in internal porosity leads to the eventual collapse of the matrix, a process which occurs, but less rapidly, in the degradation of the unblended PHB-PHV copolymers. Information obtained from molecular weight and crystallinity studies enabled a comprehensive profile of the overall degradation process to be built up.

Polymers for biodegradable medical devices. II. Hydroxybutyrate-hydroxyvalerate copolymers: hydrolytic degradation studies

The hydrolytic degradation of poly(hydroxybutyrate) together with a series of hydroxybutyrate-hydroxyvalerate copolymers has been studied. The effects of copolymer composition and molecular weight are presented together with the results of varying pH and temperature on the degradation rate. Degradation has been monitored by weight loss and water uptake measurements together with goniophotometric, surface energy and scanning electron microscopic studies. Some comparisons with the more widely used so-called 'biodegradable' polymers, poly(glycolic acid), poly(dioxanone) and the glycolic-lactic acid (90:10) copolymers are presented together with the effect of blood plasma on the degradation process.

The importance of communication with the foci of infection in the transmission of filariasis in Indonesia

Studies on the occurrence of early symptoms of filariasis have been conducted in two transmigration Units in the valley of the Wae Apu river, Buru island, Maluku Province, Indonesia. In both Units, higher disease rates were found in areas, where there was a closer contact with positive natives, higher density of the vector mosquito, and higher infective rates in the mosquitoes.