Changes in frequency and force production of the human myometrium with alteration of pH and metabolism

Changes in uterine metabolism and intracellular pH occur with uterine activity and these may in turn alter function. We have investigated the effects of changes in intracellular pH and metabolic inhibition on the spontaneous activity of isolated nonpregnant and pregnant human myometrial strips at 37 degrees C. Intracellular alkalinization resulted in a marked increase in the frequency of contractions in both nonpregnant and pregnant preparations. Intracellular acidification reduced force production in pregnant and nonpregnant preparations. The effects of pH were concentration dependent. Metabolic inhibition (2 mmol cyanide l-1) abolished spontaneous contractions in nonpregnant preparations (ten of ten) but pregnant preparations were able to maintain activity, although at a reduced level (eleven of fifteen). Possible mechanisms involved and relevance to uterine dysfunction are discussed.

Uterine contraction and physiological mechanisms of modulation

Control of the smooth muscle in the uterus (the myometrium), is of vital importance during pregnancy and parturition. It is therefore understandable that several physiological mechanisms (neuronal, hormonal, metabolic, and mechanical) play a role in the control of myometrial activity. As our knowledge of the mechanism of uterine contraction has increased much in recent years, it is now possible to begin to explain, in some detail, how the contractile activity may be modulated. A detailed account of the mechanism of contraction in the uterus is therefore given, followed by examples of modulation of this process for each of the four physiological methods listed above. Examples have been chosen to illustrate either general or particular mechanisms of modulation. The goal of many working in this field is to understand these processes and thus prevent preterm labor and uterine dysfunction in term labor, which are still significant clinical problems.

The effects of intracellular and extracellular alkalinization on contractions of the isolated rat uterus

The effects of changing pH on a spontaneously active smooth muscle, the myometrium, is examined. We show, for the first time in any smooth muscle, that the frequency of contraction is greatly increased when intracellular pH is raised. Three weak bases, trimethylamine, diethylamine and ammonium, were used to raise intracellular pH (pHi), at constant external pH, in isolated uteri of pregnant and non-pregnant rats. Each base increased spontaneous uterine contractile activity, particularly by raising the frequency, in a concentration-dependent manner. At the highest concentrations (40-50 mM) frequency was so increased that a maintained contraction resulted. Intracellular alkalinization during a high-K-maintained uterine contraction produced a small, but significant, fall in force. When external pH was increased, the results were greatly influenced by gestational state; in uteri from non-pregnant animals there was no effect whereas uteri from pregnant rats were found to be extremely sensitive to a raised external pH above 7.4; spontaneous contractions were reduced. In pregnant uteri, when both internal and external pH were elevated, spontaneous contractions were immediately reduced, thus the effects of external pH predominated. These findings may have significance in labour.

The effects of metabolic inhibition and acidification on force production in the rat uterus

The effects of hypoxia and intracellular acidification were examined on the mechanical properties of the non-pregnant and pregnant rat uterus. Isolated uteri were investigated during control conditions and in the presence of cyanide, to simulate hypoxia or the salts of weak acids and bases to change intracellular pH at constant external pH (pH 7.4). Both spontaneous contractions and high-K contractures (i.e. fully activated preparations) were investigated at 37 degrees C. In control solutions both pregnant and non-pregnant uteri were spontaneously active and gave a contracture when bathed with a high-K+ solution. When oxidative phosphorylation was inhibited by cyanide, spontaneous contractions were either greatly reduced or abolished. The effects on spontaneous contractions were more pronounced in the non-pregnant than the pregnant uterus. If high-K solution was added after cyanide had abolished spontaneous contractions, then a small amount of force was produced. High-K-induced contractures were not maintained in the presence of cyanide and quickly fell to baseline levels in both pregnant and non-pregnant uteri. All the effects of cyanide were fully reversible. When only intracellular pH was changed by adding weak acids (50 mM-butyrate or propionate), spontaneous contractions were greatly diminished or abolished in both pregnant and non-pregnant uteri. However, the application of weak acids had no effect upon the KCl-induced contractures in both pregnant and non-pregnant uteri. The effects of cyanide on the uterus include both an acidification and changes in metabolites, e.g. a fall in [ATP]. To investigate the changes in metabolites without a change in pHi, cyanide was applied with the weak base trimethylamine (40-50 mM). 31P Nuclear magnetic resonance spectroscopy was used to show that the alkalinization which occurs with trimethylamine alone abolished the acidification ordinarily associated with cyanide. Spontaneous and high-K-induced contractions were greatly reduced or abolished, i.e. the result was the same as with cyanide alone. This occurred in both pregnant and non-pregnant uteri. It is concluded that spontaneous force production is affected by both changes in metabolites (e.g. decreased [ATP] and increased inorganic phosphate) and pHi, and that both can depress activation of the uterus. Only the changes in metabolites can depress force production in fully activated preparation. The greater effect on force in the non-pregnant uterus compared to the pregnant uterus may be due to the lower initial levels of [ATP] and the greater fall in ATP seen in non-pregnant compared to pregnant uterus, and gestational changes in metabolism.(ABSTRACT TRUNCATED AT 400 WORDS)

Spatially restricted expression of a member of a new family of murine Distal-less homeobox genes in the developing forebrain

The homeobox genes of Drosophila perform key functions in embryonic pattern formation, and their vertebrate counterparts may play similar developmental roles. Using polymerase chain reaction technology, we have identified four murine homologs of the Drosophila Distal-less homeobox gene that are expressed in midgestation embryos. The homeodomains encoded by these genes vary considerably from other known homeodomain sequences and represent a new family of vertebrate homeobox genes. We isolated a cDNA for one of these genes (Dlx-2) and studied its expression by in situ hybridization from 8.5 days postcoitum (pc) until postnatal day 1. Dlx-2 shows a restricted pattern of expression in the ventral forebrain, extending from the olfactory bulb to the ventral diencephalon. This domain of expression may delineate an ontogenetically defined subdivision within the forebrain. The murine Distal-less genes are the first homeobox genes described whose expression in the central nervous system is exclusively restricted to the forebrain. Thus, the Distal-less genes may contribute missing positional cues not provided by the previously identified vertebrate homeobox genes.

Maintenance of LHRH and oxytocin neurons in slice explants cultured in serum-free media: effects of tetrodotoxin on gene expression

A variety of neuroendocrine cells survive and express specific neuropeptide genes for long periods of time in slice explant cultures in the presence of serum. However, before use of these slice explant cultures as experimental models for physiological and pharmacological studies on the regulation of neuropeptide gene expression, it is first necessary to evaluate their characteristics in defined (e.g. serum free) media and to control for the spontaneous electrical and synaptic activity of neurons in these cultures. In this study, brain slices from postnatal day 4 rats were cultured in serum-containing media (SCM) for 12 days to allow thinning, and then maintained in a serum-free, defined media (SFM) for 6 days. Culture slices transferred to SFM appeared healthy and numerous neuroendocrine neurons containing messenger RNA (mRNA) encoding for LHRH and magnocellular neurons containing mRNA encoding for oxytocin (OT) were detected using in situ hybridization histochemistry (ISHH). Each of these neuronal subtypes robustly produced their appropriate gene products as determined by immunocytochemical analysis. Abundant magnocellular OT neurons were found in cultures grown in either SCM or SFM. In contrast, magnocellular vasopressin (VP) neurons were rarely detected under these conditions. Inhibition of spontaneous electrical and synaptic activity in these slice explant cultures was effectively achieved by incubation for the last 2.5 days of culture in the presence of tetrodotoxin (TTX; 10(-6) M). Densitometric single cell analyses after ISHH was performed on both LHRH and OT cells. Comparisons of the density values (corresponding to mRNA levels), from these slice explants, found that: (1) cellular LHRH mRNA levels decreased in the absence of serum, whereas cellular OT mRNA levels did not significantly change under these conditions; (2) the presence of TTX in the media resulted in an overall decrease in cellular LHRH mRNA values in both SCM and SFM, and (3) the OT neurons in these slice cultures appear to be composed of a heterogeneous population, with one cell subtype responding to TTX with an increase in cellular OT mRNA levels. These data show that factors in serum and spontaneous electrical activity can differentially influence mRNA levels of LHRH cells and magnocellular OT neurons in culture.

Intracellular pH and buffering power measured in isolated single cells from pregnant rat uterus

Intracellular pH (pHi) affects smooth muscle function yet there have been few direct pHi measurements. Using the fluorescent indicator, 2',7'-bis-2-(carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester, we report here the first measurements of pHi and buffering power (beta) in single, isolated, uterine smooth muscle cells. Mean pHi in cells from pregnant rat uteri was 7.09 +/- 0.08 (+/- S.E.M., n = 16 cells; 37 degrees C), and beta was found to be 12.8 +/- 2.8 mmol/l per pH unit (n = 15). The cells were able to regulate their pHi in the presence of butyrate when perfused in nominally CO2-free solution.

Migratory arrest of gonadotropin-releasing hormone neurons in transgenic mice

Gonadotropin-releasing hormone (GnRH) is important in reproduction, although the mechanism of central hypogonadism in humans remains unclear. Because the GnRH neuron originates from the olfactory placode and migrates to the hypothalamus during development, central hypogonadism in humans could be caused by failure in normal migration of GnRH neurons to the hypothalamus. We report that in transgenic mice expression of the simian virus 40 T antigen, driven by the promoter of human GnRH gene, resulted in central hypogonadism due to an arrest in neuronal migration during development and tumor formation along the migratory pathway. This system appears to be an important animal model of hypogonadotropic hypogonadism in humans. Additionally, olfactory bulb tumors from these animals were dispersed, and a GnRH-secreting neuronal cell line (GN cell line) was established.

Cytochrome oxidase content of rat brain during development

The cytochrome oxidase concentration and content of rat brain during development was measured using a simple new assay for cytochrome a. The cytochrome oxidase concentration increased from 1.2 nmol/g wet wt. of brain at birth to about 5.5 nmol/g in the adult, most of the change occurring between 5 and 25 days after birth.

Neurochemical anatomy of fetal hippocampus transplanted into large lesion cavities made in the adult rat brain

The purpose of the present study was to determine whether neurochemicals normally found within neuron somata, fibers, and terminals of the hippocampal formation would also be present in transplanted hippocampal tissue that had developed in lesion cavities made in adult rat brains by aspiration of the hippocampus and overlying dorsolateral neocortex. Embryonic Day 15 or 16 rat brian tissue containing hippocampus with some medial pallial anlage was transplanted into the site of hippocampal aspiration lesions in adult male rats. One hundred ten to one hundred thirty-five days later the brains of these rats were sectioned and processed using the avidin-biotin-horseradish peroxidase immunocytochemical procedure to visualize choline acetyltransferase, met-enkephalin (MENK), neurotensin (NT), somatostatin, substance P, tyrosine hydroxylase (TH), or vasoactive intestinal polypeptide. Sections from two brains were stained using the thiocholine technique for visualization of acetylcholinesterase. All of these substances were found within cell bodies and/or fibers in the transplants. However, several abnormalities were noted. In addition to TH-immunoreactive fibers, TH-immunoreactive cell bodies were found in the transplants. Since TH is not expressed in mature hippocampal or cortical neurons this suggests that mechanisms for suppression of manufacture of this enzyme are lacking or inhibited in the transplants. Further, although all of the peptides were present either in fibers or in both cell bodies and fibers, the density of staining for NT and MENK was less than would be expected for normal hippocampus, and none of the cell bodies or fibers reacting for the peptides exhibited any apparent organization resembling that normally observed in hippocampus or cortex. However, some histological organization was present and the cholinergic markers were associated with this organization. These data suggest that some tropic and/or trophic factor such as nerve growth factor is present in the transplants to guide cholinergic innervation.

The effects of metabolic inhibition on uterine metabolism and intracellular pH in the rat

1. Uterine metabolism was studied in pregnant and non-pregnant rats by measuring high energy phosphates and intracellular pH (with 31-phosphorus nuclear magnetic resonance (31P NMR) spectroscopy) and lactic acid efflux. Isolated, superfused uteri were investigated during control conditions (30 degrees C) and in the presence of metabolic inhibitors and high [K+]. 2. In control conditions the ratio of phosphocreatine and ATP concentrations ([PCr]/[ATP]) was higher in the pregnant (0.88 +/- 0.09) than the non-pregnant uterus (0.52 +/- 0.04). When oxidative phosphorylation was inhibited by cyanide, there was a significant (P less than 0.01) decrease in [PCr] and [ATP] and an increase in the concentration of inorganic phosphate ([Pi]). These changes were greater in the non-pregnant than the pregnant uterus. 3. There was no difference in the mean value of resting pHi found in pregnant and non-pregnant uterus (7.19 +/- 0.04 and 7.17 +/- 0.03, external pH 7.4, n = 10 and 12 respectively). There was a significant intracellular acidification in both pregnant (0.31 +/- 0.04 pH unit) and non-pregnant (0.27 +/- 0.02 pH unit) uterine tissue in the presence of cyanide. These effects of cyanide on metabolites and pHi were fully reversed upon return to control solutions. 4. When both aerobic and anaerobic glycolysis were blocked by iodoacetate, there was a rapid disappearance of high energy phosphates from the 31P NMR spectrum and a large increase in the phosphomonoester spectral region, where sugar phosphate intermediates of glycolysis resonate. These changes were seen in both pregnant and non-pregnant uteri and were irreversible. 5. Lactate production was detected, in the presence of oxygen, in both pregnant and non-pregnant preparations (0.43 +/- 0.07 and 0.25 +/- 0.09 mumols g-1 min-1, respectively). In both preparations the rate of lactate production was markedly increased in the presence of cyanide. The increase was much more marked in non-pregnant (approximately 10-fold) than pregnant (approximately 5-fold) uteri, resulting in a very similar rate of lactate efflux in cyanide. 6. When lactate efflux in non-pregnant uteri was blocked by alpha-cyano-4-hydroxycinnamate, there was a significant acidification (0.21 +/- 0.04 pH unit, n = 6). The addition of cyanide produced a more pronounced acidification (0.34 +/- 0.04 pH unit) than that seen with either cyanide or alpha-cyano-4-hydroxycinnamate alone.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantitation of cerebral blood volume in human infants by near-infrared spectroscopy

Current methods for measuring cerebral blood volume (CBV) in newborn infants are unsatisfactory. A new method is described in which the effect of a small change (5-10%) in arterial oxygen saturation (SaO2) on cerebral oxyhemoglobin [HbO2] and deoxyhemoglobin [Hb] concentration is observed by near-infrared (NIR) spectroscopy. Previous experiments in which the NIR absorption characteristics of HbO2 and Hb and the pathlength of NIR light through the brain were defined allowed changes in [HbO2] and [Hb] to be quantified from the Beer-Lambert law. It is shown here that CBV can then be derived from the expression CBV = (delta[HbO2] - delta[Hb])/(2. delta SaO2.H.R.), where H is the large vessel total hemoglobin concentration and R to the cerebral-to-large vessel hematocrit ratio. Observations on 12 newborn infants with normal brains, born at 25-40 wk of gestation and aged 10-240 h, gave a mean value for CBV of 2.22 +/- 0.40 (SD) ml/100 g, whereas mean CBV was significantly higher 3.00 +/- 1.04 ml/100 g in 10 infants with brain injury born at 24 to 42 wk of gestation and aged 4-168 h (P less than 0.05).

Evidence that cells expressing luteinizing hormone-releasing hormone mRNA in the mouse are derived from progenitor cells in the olfactory placode

In situ hybridization histochemistry and immunocytochemistry were used to study the prenatal expression of luteinizing hormone-releasing hormone (LHRH) cells in the mouse. Cells expressing LHRH mRNA and peptide product were first detected on embryonic day 11.5 (E11.5) in the olfactory pit. On E12.5, the majority of LHRH cells were located on "tracks" extending from the olfactory pit to the base of the telencephalon. From E12.5 to E15.5, LHRH cells were detected in a rostral-to-caudal gradient in forebrain areas. Prior to E12.5, cells expressing LHRH mRNA were not detected in forebrain areas known to contain LHRH cells in postnatal animals. Quantitation of cells expressing LHRH mRNA showed that the number of labeled cells on E12.5 (approximately 800) equaled the number of LHRH cells in postnatal animals, but more than 90% of these cells were located in nasal regions. Between E12.5 and E15.5, the location of LHRH cells shifted. The number of LHRH cells in the forebrain increased, while the number of LHRH cells in nasal regions decreased over this same period. These findings establish that cells first found in the olfactory pit and thereafter in forebrain areas express the LHRH gene and correspond to the position of LHRH immunopositive cells found at these developmental times. To further examine the ontogeny of the LHRH system, immunocytochemistry in combination with [3H]thymidine autoradiography was used to determine when LHRH cells left the mitotic cycle. We show that LHRH neurons exhibit a discrete time of birth, suggesting that they arise as a single neuronal population between E10.0 and E11.0. Postnatal LHRH neurons were "birth-dated" shortly after differentiation of the olfactory placode and before LHRH mRNA was expressed in cells in the olfactory pit. Taken together, these studies support the hypothesis that all LHRH cells in the central nervous system arise from a discrete group of progenitor cells in the olfactory placode and that a subpopulation of these cells migrate into forebrain areas where they subsequently establish an adult-like distribution.

Differential effects of estrogen on luteinizing hormone-releasing hormone gene expression in slice explant cultures prepared from specific rat forebrain regions

Five serially sectioned tissue slices (400 microns) from the preoptic area/hypothalamus of postnatal day 4 rats were cultured using a slice explant roller culture technique. After 18 days in culture, these slices thinned sufficiently to allow immunocytochemical and in situ hybridization histochemical assays for LHRH peptide and LHRH mRNA, respectively. Large numbers of neurons containing mRNA encoding LHRH were detected in these slices using in situ hybridization histochemistry (ISHH). These 35S-labeled cells were distributed in the cultured slices in a pattern similar to that found with LHRH immunocytochemistry and ISHH in vivo, indicating that LHRH neurons were maintained in these cultures in an organotypic manner. Densitometric single cell analyses after ISHH of the culture slices were performed using a Loats image analysis system, so as to provide a density value per cell (density/cell). Comparisons of these density values from the slice explants cultured in presence or absence of 10(-7) M estradiol found that: 1) under basal (control) culture conditions there were no consistent differences in the frequency distributions of the density/cell values between all the five slices derived from either male or female rats, 2) mean density/culture values under control conditions did not differ significantly between slices and sexes, 3) the presence of estradiol in the culture media resulted in an overall decrease in density/cell values, with the most significant decrease occurring in slice 3 which is comparable to the level of the organum vasculosum lamina terminalis/rostral preoptic area (OVLT/rPOA) in vivo, and 4) this decrease in density/cell values in slice 3 due to estradiol treatment, was greater in cultures derived from female vs. male tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurovisual outcome following proton radiation therapy

From February 1981 to January 1984, 20 patients with a tumor of the upper clivus received proton irradiation at the Harvard Cyclotron Laboratory. For 15 patients with known neurovisual status (including visual acuity, color vision, visual field, and fundus examinations) we obtained a cumulative dose-volume histogram (DVH) of the optic nerves (ON) and the optic chiasm. The prescribed tumor doses ranged from 66.6 to 74.4 Cobalt Gray Equivalent (CGE) with a daily fraction size of 1.8 to 2.1 CGE. CGE is used because modulated protons have an RBE of 1.1 compared to 60Co. The follow-up ranged from 30 to 68 months (median 52). Two patients developed, 10 and 36 months post irradiation, a progressive visual deterioration affecting both eyes. This was attributed to an ON and a chiasm injury in one patient and to bilateral ON injury in the other patient. In the first patient, the dose-volume analysis indicated that approximately half of the ON and of the chiasm had received 65 CGE and 55 CGE, respectively. In the second patient, it indicated that a quarter of the left ON (LON) had received 55 CGE whereas the dose to the right ON (RON) was significantly less. This patient had diabetes mellitus which may be a predisposing factor. From this study, a complication rate of 20% (1/5) is observed when a substantial portion of the ON is taken to 65 CGE, while it doesn't exceed 12.5% (2/16) and 7.5% (1/13) at 55 CGE for the ON and for the chiasm, respectively. This suggests a tolerance dose implying a 10% rate of major complications close to 55 CGE. When a tumor requires a high radiation-dose, the exclusion of these structures at 55 to 60 Gy is recommended.

Spatiotemporal cell expression of luteinizing hormone-releasing hormone in the prenatal mouse: evidence for an embryonic origin in the olfactory placode

The spatiotemporal cell expression of luteinizing hormone-releasing hormone (LHRH) was investigated in mice during prenatal development using light microscopic immunocytochemistry. LHRH immunoreactive cells were first detected in the epithelium of the olfactory pit on gestational day 11 1/2 (E11.5). Some LHRH cells were just outside the olfactory epithelium (OE), clustered on short 'tracks' which extended dorsocaudally. Immunopositive LHRH cells were not observed in any other regions. At E12.5, immunopositive cells were still detected in the OE, but now many LHRH cells were clustered on 'tracks' within olfactory areas. These 'tracks' started at the OE, bilaterally, and extended towards and abutted the basal telencephalic hemispheres. Some immunopositive cells were detected in the rostral telencephalon but not caudal to the telencephalon. The LHRH cells outside the OE were unipolar or bipolar, morphologically resembled mature LHRH neurons and appeared to contact neighboring LHRH cells. The distribution of LHRH cells at E13.5 was similar to E12.5, with the exception that immunopositive cells now extended from the telencephalon to the rostral diencephalon. From E14.5 to E17.5 the majority of LHRH cells were located within the forebrain; extending throughout the diencephalon. Immunopositive cells were not detected in the OE, but were scattered rostrocaudally in olfactory septal areas. By E16.5, LHRH cells within the brain were distributed in a pattern similar to that of the adult mouse. These findings illustrate that LHRH cells express their peptide phenotype early in ontogeny and before their distribution in the forebrain is detected. These data are consistent with the hypothesis that LHRH cells are derived from the olfactory placode and migrate into the forebrain during prenatal development.

Prenatal ontogenesis of pro-opiomelanocortin in the mouse central nervous system and pituitary gland: an in situ hybridization and immunocytochemical study

Pro-opiomelanocortin (POMC) mRNA detected by in situ hybridization and POMC/ACTH (adrenocorticotropin)-containing neurons detected by immunocytochemistry were first observed in the presumptive arcuate nucleus of embryonic mouse brain on gestational day 10.5 (E10.5). Immunostained fibers were also evident on E10.5 in the lateral and dorsal diencephalon. In these areas, a dense network of processes developed by E11.5 and extended into the mesencephalon. Fibers were detected in the myelencephalon at this stage and a day later (E12.5) in the spinal cord. Adult-like patterns of POMC/ACTH fibers were established in the diencephalon, mesencephalon, metencephalon and the myelencephalon between E13.5 and E15.5. POMC-expressing cells in the anterior and intermediate lobes of the pituitary gland appeared on E12.5 and E14.5, respectively. The early expression of POMC and the rapid establishment of dense fiber tracts in the brain is consistent with a role for POMC-derived peptides in the development of the central nervous system.

Regulation of intracellular pH in rat uterine smooth muscle, studied by 31P NMR spectroscopy

Intracellular pH (pHi) affects smooth muscle function, yet little is known concerning its regulation. I have therefore investigated pH regulation in rat uterus, using 31P-NMR spectroscopy. A change in extracellular pH(pHe) of 1 pH unit (7.4 to 6.4) elicited a 0.29 change in pHi; smaller changes in pHe were accompanied by proportionately smaller changes in pHi. The pH changes were reversible. There was no fall of uterine ATP or phosphocreatine during the pH changes.

Estimation of optical pathlength through tissue from direct time of flight measurement

Quantitation of near infrared spectroscopic data in a scattering medium such as tissue requires knowledge of the optical pathlength in the medium. This can now be estimated directly from the time of flight of picosecond length light pulses. Monte Carlo modelling of light pulses in tissue has shown that the mean value of the time dispersed light pulse correlates with the pathlength used in quantitative spectroscopic calculations. This result has been verified in a phantom material. Time of flight measurements of pathlength across the rat head give a pathlength of 5.3 +/- 0.3 times the head diameter.

Estimation of optical pathlength through tissue from direct time of flight measurement

Quantitation of near infrared spectroscopic data in a scattering medium such as tissue requires knowledge of the optical pathlength in the medium. This can now be estimated directly from the time of flight of picosecond length light pulses. Monte Carlo modelling of light pulses in tissue has shown that the mean value of the time dispersed light pulse correlates with the pathlength used in quantitative spectroscopic calculations. This result has been verified in a phantom material. Time of flight measurements of pathlength across the rat head give a pathlength of 5.3 +/- 0.3 times the head diameter.